Endangered and Threatened Wildlife and Plants; Critical Habitat Designation for Four Vernal Pool Crustaceans and Eleven Vernal Pool Plants in California and Southern Oregon
Federal RegisterSep 24, 2002
Ask Donna
What actually matters in this document.
Text
DEPARTMENT OF THE INTERIOR
Fish and Wildlife Service
50 CFR Part 17
RIN 1018-AI26
Endangered and Threatened Wildlife and Plants; Critical Habitat Designation for Four Vernal Pool Crustaceans and Eleven Vernal Pool Plants in California and Southern Oregon
AGENCY:
Fish and Wildlife Service, Interior.
ACTION:
Proposed rule.
SUMMARY:
We, the Fish and Wildlife Service (Service), propose designation of critical habitat for 4 vernal pool crustaceans and 11 vernal pool plants with a total area being proposed of approximately 672,920 hectares (ha) (1,662,762 acres (ac)). The proposed designation of critical habitat is for Conservancy fairy shrimp (
Branchinecta conservatio
) 165,820 ha (409,735 ac), longhorn fairy shrimp (
Branchinecta longiantenna
) 40,605 ha (100,333 ac), vernal pool fairy shrimp (
Branchinecta lynchi
) 457,556 ha (1,130,605 ac), and vernal pool tadpole shrimp (
Lepidurus packardi
) 291,370 ha (719,965 ac) (collectively referred to as “vernal pool crustaceans” in the remainder of this document), and Butte County meadowfoam (
Limnanthes floccosa
ssp.
californica
) 16,320 ha (40,326 ac), Contra Costa goldfields (
Lasthenia conjugens
) 14,499 ha (38,297 ac), Hoover's spurge (
Chamaesyce hooveri
) 81,744 ha (201,987 ac), succulent (or fleshy) owl's-clover (
Castilleja campestris
ssp.
succulenta
) 125,217 ha (309,407 ac), Colusa grass (
Neostapfia colusana
) 132,608 ha (327,670 ac), Greene's tuctoria (
Tuctoria greenei
) 142,984 ha (353,308 ac), hairy Orcutt grass (
Orcuttia pilosa
) 65,671 ha (162,272 ac), Sacramento Orcutt grass (
Orcuttia viscida
) 24,632 ha (60,865 ac), San Joaquin Valley Orcutt grass (
Orcuttia inaequalis
) 101,059 ha (249,714 ac), slender Orcutt grass (
Orcuttia tenuis
) 71,035 ha (175,524 ac), and Solano grass (
Tuctoria mucronata
) 7,345 ha (18,149 ac) (collectively referred to as “vernal pool plants” in the remainder of this document), pursuant to the Endangered Species Act of 1973, as amended (Act). Because many of the units proposed for different species overlap, the total critical habitat area we are proposing is much less than the sum of the areas for each species. The proposed units are in 39 counties in California and one county in southern Oregon.
If this proposed rule is made final, section 7 of the Act would prohibit destruction or adverse modification of critical habitat by any activity funded, authorized, or carried out by any Federal agency. Section 4 of the Act requires us to consider economic and other impacts of specifying any particular area as critical habitat.
We solicit data and comments from the public on all aspects of this proposal, including data on the economic and other impacts of the designation. We may revise or further refine critical habitat boundaries prior to final designation based on habitat and additional plant and animal surveys, public comments on the proposed critical habitat rule, the completion and approval of Habitat Conservation Plans (HCPs), and new scientific and commercial information, and data concerning potential economic impacts from the proposed designation.
DATES:
We will accept comments from all interested parties until November 25, 2002. Public hearing requests must be received by November 8, 2002.
ADDRESSES:
If you wish to comment, you may submit your comments and materials concerning this proposal by any one of several methods.
1. You may mail written comments and information to the Field Supervisor, Sacramento Fish and Wildlife Office, U.S. Fish and Wildlife Service, 2800 Cottage Way, Room W-2605, Sacramento, CA 95825.
2. You may hand deliver written comments to our Sacramento Fish and Wildlife Office at the address given above.
3. You may send comments by electronic mail (e-mail) to
fw1_vernalpool@fws.gov.
See the Public Comments Solicited section below for file format and other information about electronic filing.
Comments and materials received, as well as supporting documentation used in the preparation of this proposed rule, will be available for public inspection, by appointment, during normal business hours at the above address.
FOR FURTHER INFORMATION CONTACT:
Arnold Roessler or Susan Moore, at the Sacramento Fish and Wildlife Office address above (telephone 916/414-6600; facsimile 916/414-6710). Information regarding this proposal is available in alternate formats upon request.
SUPPLEMENTARY INFORMATION:
Background
The vernal pool crustaceans and plants addressed in this proposed rule live in vernal pools (shallow depressions that hold water seasonally), swales (shallow drainages that carry water seasonally), and ephemeral freshwater habitats. None are known to occur in riverine waters, marine waters, or other permanent bodies of water. The vernal pool habitats of the four vernal pool crustaceans and eleven plants addressed in this proposed rule have a discontinuous distribution west of the Sierra Nevada that extends from southern Oregon through California into northern Baja California, Mexico (Holland and Jain 1978, 1988, Eriksen and Belk 1999).
Vernal pools are a unique kind of wetland ecosystem. Central to their distinctive ecology is the fact that they are vernal or ephemeral, occurring temporarily—typically during the spring—and then disappearing until the next year. They are wet long enough to be different in character and species composition from the surrounding upland habitats, and yet their prolonged annual dry phase prevents the establishment of species typical of more permanent wetlands. In California, where extensive areas of vernal pool habitat developed over long periods of time, unique suites of species specially adapted to the unusual conditions of vernal pools have evolved. Fish and other predators are among the species excluded by vernal pools' annual drying, so vernal pool communities have developed and flourished in the absence of many predators. California vernal pools are also renowned for their showy displays of wildflowers, blooming in concentric rings about the pools in spring. Centres of Plant Diversity, a project of the World Wide Fund for Nature (WWF) and IUCN—The World Conservation Union, has identified the vernal pools of California and Baja California, Mexico, as a center of plant diversity and endemism in North America, and considers them to be severely threatened (WWF and IUCN 2002).
Many areas in California and portions of southern Oregon have the combination of environmental conditions that favors the development of vernal pools (Keeley and Zedler 1998). The climate is of a type classified as Mediterranean, with a wet season when rainfall exceeds evaporation, filling the pools, and a dry season when evaporation is greater, drying the pools. Rainfall is relatively meager even in most wet seasons, so erosion by overflowing waters does not dissect the topographic irregularities that form vernal pool basins. Temperatures during the winter-spring wet season are mild, so plants and animals can grow, mature, and reproduce.
A second major factor in the development of vernal pools is soil. Vernal pools form where there is a soil layer below or at the surface that is impermeable or nearly impermeable to water (Smith and Verrill 1998). Precipitation and surface runoff become trapped or “perched” above this layer. In California, the restrictive soil layers underlying vernal pools are of four main types—hardpans, claypans, volcanic flows, and non-volcanic rock. Volcanic flows include basaltic lavas and cemented mudflows, and are most common along the lower western slope of the Sierra Nevada. Hardpans are formed by leaching, redeposition, and cementing of silica minerals from high in the soil profile to a lower (“B”) horizon (Hobson and Dahlgren 1998, Smith and Verrill 1998). Claypans are formed by another redeposition process—fine clay particles are transported to the B horizon and accumulate there. Claypans may also be augmented by redeposition of saline or alkaline compounds. Hardpans and claypans both develop gradually over thousands of years, and can be a meter (yard) or more thick. Smith and Verrill (1998) list many of the soil series associated with vernal pools in the Central Valley.
A third factor, related to soil and climate, is topography or relief. Vernal pools typically occur in landscapes that, at a broad scale, are shallowly sloping or nearly level, but on a fine scale may be quite bumpy. Complex micro-relief results in shallow, undrained depressions that form vernal pools. Some vernal pool landscapes are dotted with numerous, rounded soil mounds, referred to as mima mounds, after the well-developed mounds of the Mima Prairie in Thurston County, Washington (Scheffer 1947). Scientists still argue about the origins of these mounds, which have been attributed to forces as disparate as gophers acting over millennia (Scheffer 1947, Cox and Gakahu 1983) and the pressures of soil swelling and shrinkage during wetting and drying cycles (Hallsworth
et al.
1955, Hobson and Dahlgren 1998)—as well as other hypotheses, many much less plausible. Focusing on the troughs rather than the mounds, Californians long referred to vernal pools as “hog wallows,” but unlike the buffalo wallows of the Great Plains, these wetlands have little to do with hogs or wallowing. From the air, vernal pool landscapes often show characteristic patterning, produced by plant responses to mound and trough micro-relief. This patterning has allowed detailed mapping of vernal pool habitats throughout California's Central Valley and adjacent areas (Holland 1998).
Vernal pools come in a variety of shapes and sizes, from a square meter (yard) to a hectare (2.5 ac) or more. Some larger vernal wetlands, such as the 36 ha (90 ac) Olcott Lake in the Jepson Prairie Preserve in Solano County, are also referred to as vernal lakes or playa pools or lakes. Playa pools with high alkalinity are termed alkali sinks. These larger wetlands contain many of the same animals and plants of smaller vernal pools, including many rare and endangered species.
Since appropriate combinations of climate, soil, and topography often occur over continuous areas rather than in isolated spots, vernal pools in California, particularly in the Central Valley, tend to occur in clusters, called “complexes.” A landscape that supports a vernal pool complex is typically a grassland, with areas of obstructed drainage that form the pools. Vernal pools can also be found in a variety of other habitats, including woodland, desert, and chaparral. The pools may be fed or connected by low drainage pathways called “swales.” Swales are often themselves seasonal wetlands that remain saturated for much of the wet season, but may not be inundated long enough to develop strong vernal pool characteristics. Vernal pool complexes have historically been considered poor farmland, because of their shallow, seasonally saturated or inundated and sometimes alkaline soils, and their root-restricting subsurface layer. For the same reasons, trees are relatively rare in most vernal pool complexes.
California's vernal pools begin to fill with the fall and winter rains. Before ponding occurs, there is a period during which the soil is wetted and the local water table may rise. Some pools have a substantial watershed that contributes to their water inputs; others may fill almost entirely from rain falling directly into the pool (Hanes and Stromberg 1998). Although exceptions are not uncommon, the watershed generally contributes more to the filling of larger or deeper pools, especially playa pools. Even in pools filled primarily by direct precipitation, Hanes and Stromberg (1998) report that subsurface inflows from surrounding soils can help dampen water level fluctuations during late winter and early spring. Vernal pools exhibit four major phases—the wetting phase, when vernal pool soils become saturated; the aquatic phase, when a perched water table develops and the vernal pool contains water; a water-logged drying phase, when the vernal pool begins loses water as a result of evaporation and loss to the surrounding soils but soil moisture remains high; and the dry phase, when the vernal pool and underlying soils are completely dry (Keeley and Zedler 1998). Upland areas associated with vernal pools are also an important source of nutrients to vernal pool organisms (Wetzel 1975). Vernal pool habitats derive most of their nutrients from detritus which is washed into the pool from adjacent uplands, and these nutrients provide the foundation for vernal pool aquatic communities food chain. Detritus is a primary food source for the vernal pool crustaceans addressed in this proposed rule (Eriksen and Belk 1999).
Both the amount and timing of rainfall in California vary greatly from year to year. As a result, pools may fill to different extents at different times. The duration of ponding of vernal pools also varies, and in certain years some pools may not fill at all. Many characteristics of vernal pool plants and animals are adaptations to the highly variable and unpredictable nature of vernal pools (Holland 1976, Holland and Dains 1990, King
et al.
1996, Hanes and Stromberg 1998).
California's vernal pools are rich in species composition compared to vernal pools worldwide and contain many species that are endemic to the region (found nowhere else). In addition, while most of California's grasslands are now dominated by non-native grasses and other introduced plants, vernal pools remain a haven for native species. Invasive non-native plants have been introduced into California and have so successfully spread and reproduced in upland habitats that it is not unusual for non-natives to account for a third of the species and more than 90 percent of the biomass in a California grassland. Vernal pools have dramatically resisted this invasion with 75 to 95 percent of plant species found in vernal pools being native; and natives dominate in biomass as well as number (Holland and Jain 1978, Jokerst 1990, Spencer and Rieseberg 1998). Vernal pool communities dominated by natives persist even though they are surrounded by seas of grassland raining the seed of non-native plants. Vernal pool plant communities are able to resist invasion because of the severe ecological constraints on plants living in vernal pool environments.
The animal communities that live in vernal pools also contain diverse groups of highly specialized species. The freshwater crustacean communities of vernal pools are particularly well developed (Simovich 1998). The most visible crustaceans in vernal pools are the large branchiopods (literally, “gill-
foots”), about 27 species in California, of which perhaps 10 are endemic (Helm 1998, Belk and Fugate 2000) and 6 are federally listed as threatened or endangered. The large branchiopods are easily visible to the naked eye, ranging up to 5 centimeters (cm) (2 inches (in)) in length, depending on the species. They include the fairy shrimps (Anostraca), tadpole shrimps (Notostraca), and clam shrimps (Conchostraca). Smaller crustaceans that are common in California vernal pools, many large enough to see without magnification, are water fleas (Branchiopoda—Cladocera), copepods (Copepoda), and seed shrimp (Ostracoda).
Amphibians and many insect species also live in vernal pools. The Pacific tree frog (chorus frog) (
Hyla
(
Pseudacris
)
regilla
) and western toad (
Bufo boreas
) are common and abundant in and around vernal pools. Two rarer amphibians native to vernal pools are the California tiger salamander (
Ambystoma californiense
) and the western spadefoot toad (
Scaphiopus
(
Spea
)
hammondii
) (Morey 1998). While dispersing bullfrogs (
Rana catesbeiana
), which are not native to California, are sometimes found in vernal pools, they do not successfully breed there because bullfrog tadpoles require two years to mature and cannot survive the dry season. These voracious introduced predators will sometimes be found resting and feeding in vernal pools close to more permanent water, frequently associated with human modifications of the landscape. Fish likewise do not inhabit vernal pools, except where temporarily introduced by humans (
e.g.
, mosquitofish (
Gambusia
sp.)) or by flooding of permanent waters.
The insect fauna of vernal pools is numerous, varied and primarily native, including aquatic beetles (Coleoptera—Dytiscidae, Hydrophilidae, Gyrinidae, Halipidae, Hydraenidae), aquatic bugs, including backswimmers (Hemiptera—Notonectidae), water boatmen (Corixidae), and water striders (Gerridae), springtails (Collembola), mayflies (Ephemeroptera), dragonflies and damselflies (Odonata), and various flies with aquatic larvae, including midges (Diptera—Chironomidae), crane flies (Tipulidae) and mosquitoes (Culicidae). Rogers (1998) found that mosquitoes generally made up less than 2 percent of the total macroscopic invertebrate population in natural and two-year old constructed pools—perhaps because many of the other insects listed above are predators. Vernal pool crustaceans are an important food source for a number of aquatic and terrestrial species. Aquatic predators include insects such as backswimmers (Family Notonectidae) (Woodward and Kiesecker 1994), predaceous diving beetles and their larvae (Family Dystictidae), and dragonflies and damselfly larvae (Order Odonate). Vernal pool tadpole shrimp are another significant predator of fairy shrimp.
The plants, invertebrate and vertebrate animals of vernal pools, and vernal pool landscapes in general, are important providers of food and habitat for waterfowl, shorebirds, wading birds, toads, frogs, and salamanders (Proctor
et al.
1967, Krapu 1974, Swanson 1974, Morin 1987, Simovich
et al.
1991, Silveira 1996). There is evidence that vernal pool crustaceans were used as a food source for Native Americans in California's Central Valley (Silveira 1998). During the spring, waterfowl feed on vernal pool crustaceans and other invertebrates, which are sources of protein and calcium needed for migration and egg-laying (Proctor
et al.
1967, Silveira 1998). Vernal pool complexes contribute to continuity of wetland habitats along the Pacific Flyway (a major bird migration route). Many species feed or nest near vernal pools, for example, cliff swallows (
Hirundo fulva
) glean mud from vernal pool beds for their nests, lesser nighthawks (
Chordeiles acutipennis
) nest in dry vernal pool beds, burrowing owl (
Athene cunicularia
) and gopher (
Thomomys
sp.) burrows are found in mima mounds, and many species graze or hunt along vernal pool shorelines. Before their populations were nearly eliminated by hunting and habitat alteration, elk (
Cervus
sp.) and pronghorn antelope (
Antilocarpa americana
) undoubtedly grazed vernal pool landscapes, and have been replaced by cattle. Fishing net weights found near vernal pools suggests that California's first human populations also made use of vernal pool resources, as do hunters today (Silveira 1998).
Classification of Vernal Pools
The variability of vernal pool types has led many researchers to try and classify these ephemeral habitats. (
i.e.
, Holland (1986), Sawyer and Keeler-Wolf (1995), Ferren
et al.
(1996), Smith and Verrill (1998)). Most of these efforts have focused on classifying vernal pools based on the factors that influence variation in their physical features. Primary physical features that influence vernal pool size, depth, and soil and water chemistry include soil type, geologic formation, and landform. Landforms are physical attributes of the landscape resulting from geomorphological processes such as erosion and deposition, and include features such as alluvial terraces and basins; and volcanic mudflows and lava flows.
The types and kinds of species that are found in vernal pools are largely determined by these physical factors, including pool size, depth, area, and water and soil chemistry (Holland and Griggs 1976, Zedler 1987, Holland and Dains 1990, Eng
et al.
1990, Simovich 1998). The physical characteristics of the vernal pool influences the life history characteristics of vernal pool species, such as the speed with which a species can mature and reproduce, the amount of soil moisture required for germination of plant seeds or hatching of invertebrate eggs or cysts, as well as tolerance to turbidity, total dissolved solids, and other aspects of vernal pool water chemistry.
Sawyer and Keeler-Wolf (1995) classified vernal pools according to a number of physical, geographic, and biological characteristics. They identified several general vernal pool types which correspond to the nature of the impermeable layer that underlay the vernal pool and assisted the pool to form. The vernal pools were identified as Northern Hardpan, Northern Claypan, Northern Basalt Flow, Northern Volcanic Mudflow, and Northern Ashflow vernal pools. Northern Hardpan vernal pools are generally formed on alluvial terraces with silicate-cement soil layers. These pool types are generally on acidic soils, and exhibit well developed mima mound topography found on the eastern margins of the Central Valley. Northern Claypan vernal pools are generally formed on impermeable surfaces created by an accumulation of clay particles. These pool types are often found on basin and basin rim landforms and tend to occur in the central portion of the Central Valley and tend to be alkaline. Vernal pools identified as Northern Volcanic Mudflow, Northern Basalt Flow, and Northern Volcanic Ashflow, are generally formed by an impervious bedrock layer of volcanic origin. These pool types are found on the eastern and coastal portions of the Central Valley, and tend to be small and restricted in distribution. Northern Basalt Flow vernal pools occur at greater elevations than other vernal pool types.
Vernal Pool Crustaceans Background
Conservancy fairy shrimp (
Branchinecta conservatio
), longhorn fairy shrimp (
Branchinecta longiantenna
), and vernal pool fairy shrimp (
Branchinecta lynchi
) are members of the aquatic crustacean order Anostraca. Vernal pool tadpole shrimp
(
Lepidurus packardi
) is a member of the aquatic crustacean order Notostraca. Vernal pool fairy shrimp are found in California and southern Oregon while the other three shrimp species are found only in California. These species have all evolved similar adaptations to the unique habitat conditions of their vernal pool habitats. The general appearance and life history characteristics of these four species will be described in combination below.
Longhorn fairy shrimp, vernal pool fairy shrimp, and Conservancy fairy shrimp (fairy shrimp) have delicate elongate bodies, large stalked compound eyes, and 11 pairs of phyllopods, or gill-like structures that also serve as legs. They swim or glide gracefully upside down by means of complex beating movements that pass in a wave-like anterior to posterior direction. Fairy shrimp are filter feeders, and consume algae, bacteria, protozoa, rotifers, and bits of detritus as they move through the water. The second pair of antennae in fairy shrimp adult males are greatly enlarged and specialized for clasping the females during copulation. The females carry eggs in an oval or elongate ventral sac (brood sac). Once fertilized, the eggs are coated with a protective protein layer that allows them to withstand heat, cold, and prolonged dehydration. The fully developed eggs are either dropped to the pool bottom or remain in the brood sac until the female dies and sinks. These dormant eggs are also known as cysts, and they can remain viable in the soil for decades after deposition (Eriksen and Belk, 1999). When the pools refill in the same or subsequent seasons, some, but not all, of the cysts may hatch (Eriksen and Belk, 1999). The cyst bank in the soil may consist of cysts from several years of breeding. The cysts that hatch may do so within days after the vernal pools fill, and rapidly develop into adults within weeks. In pools that persist for several weeks to a few months, fairy shrimp may have multiple hatches during a single season.
Vernal pool tadpole shrimp have dorsal compound eyes, a large shield-like carapace (shell) that covers most of their body and a pair of long cercopods or appendages at the end of the last abdominal segment. They are primarily benthic (living on the bottoms of the pools) animals that swim with their legs down. Vernal pool tadpole shrimp climb or scramble over objects, and plow along bottom sediments as they forage for food. Their diet consists of organic detritus (decaying matter) and living organisms, such as fairy shrimp and other invertebrates (Fryer 1987). The females deposit eggs on vegetation and other objects on the pool bottom. Like fairy shrimp, vernal pool tadpole shrimp pass the summer months as dormant cysts in the soil. Some of the cysts hatch as the vernal pools are filled with rainwater in the next or subsequent seasons, while other cysts may remain dormant in the soil for many years. When winter rains refill inhabited pools, tadpole shrimp reestablish from dormant cysts and may become sexually mature within three to four weeks after hatching (Ahl 1991, Helm 1998). Mature adults may be present in pools until the habitats dry up in the spring (Ahl 1991, Gallagher 1996).
All of the vernal pool crustacean species addressed in this proposed critical habitat designation have evolved unique physical adaptations to survive in vernal pools. The timing and duration of wet and dry phases can vary significantly from year to year, and in some years vernal pools may not inundate at all. In order to take advantage of the short inundation phase, vernal pool crustaceans have evolved short reproduction times and high reproductive rates. Most of the species addressed in this proposed rule hatch within a few days after their habitats fill with water, and can start reproducing within a few weeks (Eng
et al.
1990, Helm 1998, Eriksen and Belk 1999). Vernal pool crustaceans can complete their entire life cycle in a single season, and some species may complete several life cycles. Vernal pool crustaceans can also produce thousands viable cysts when environmental conditions are favorable.
To survive the prolonged heat and dessication of the vernal pool dry phase, vernal pool crustaceans have developed a dormant stage. After vernal pool crustacean eggs are fertilized in the female's brood sac, the embryos develop a thick, usually multi-layered shell. When embryonic development reaches a late stage, further maturation stops, metabolism is drastically slowed, and the egg, now referred to as a cyst, enters a dormant state called diapause. The cyst is then either dropped to the pool bottom or remains in the brood sac until the female dies and sinks. Once the cyst is desiccated, it can withstand temperatures near boiling (Carlisle 1968), fire (Wells
et al.
1997), freezing, and anoxic conditions without damage to the embryo. The cyst wall cannot be affected by digestive enzymes, and can be transported in the digestive tracts of animals without harm (Horne 1967). Most fairy shrimp cysts can remain viable in the soil for a decade or longer (Belk 1998).
Although the exact signals that cause crustacean cysts to hatch are unknown, factors such as soil moisture, temperature, light, oxygen, and osmotic pressure may trigger the embryo's emergence from the cyst (Brendonck 1996). Because the cyst contains a well developed embryo, the animal can quickly develop into a fully mature adult. This allows vernal pool crustaceans to reproduce before the vernal pool enters the dry phase, sometimes within only a few weeks (Helm 1998, Eriksen and Belk 1999). In some species, cysts may hatch immediately without going through a dormant stage, if they are deposited while the vernal pool still contains water. These cysts are referred to as quiescent, and allow the vernal pool crustacean to produce multiple generations in a single wet season as long as their habitat remains inundated.
Another important adaptation of vernal pool crustaceans to the unpredictable conditions of vernal pools is the fact that not all of the dormant cysts hatch in every season. Simovich and Hathaway (1997) found that only 6 percent of San Diego fairy shrimp cysts hatched after initial hydration, and only 0.18 percent of Riverside fairy shrimp cysts hatched. The cysts that don't hatch remain dormant and viable in the soil. These cysts may hatch in a subsequent year, and form a cyst bank much like the seed bank of annual plants. The cyst bank may be comprised of cysts from several years of breeding, and large cyst banks of viable resting eggs in the soil of vernal pools containing fairy shrimp have been well documented (Belk 1998). Based on a review of other studies (
e.g.
, Belk 1977, Gallagher 1996, Brendonck 1996), Simovich and Hathaway (1997) concluded that species inhabiting more unpredictable environments, such as smaller or shorter lived pools, are more likely to have a smaller percent of their cysts hatch after their vernal pool habitats fill with water. This strategy reduces the probability of complete reproductive failure if a vernal pool dries up prematurely. This kind of “bet-hedging strategy” has been suggested as a mechanism by which rare species may persist in unpredictable environments (Chesson and Warner 1981, Chesson and Huntly 1989, Ellner and Hairston 1994).
Although the vernal pool crustaceans, and particularly the fairy shrimp, addressed in this proposed rule are not often found in the same vernal pool at the same time, when coexistence does occur, it is generally in deeper, longer lived pools (Eng
et al.
1990, Thiery 1991, Gallagher 1996, Simovich 1998). In larger pools, closely related species of fairy shrimp may coexist by hatching at different temperatures, and by
developing at different rates (Thiery 1991, Hathaway and Simovich 1996). Vernal pool crustacean species may also be able to coexist by utilizing different physical portions of the vernal pool, or by eating different food sources (Daborn 1978, Mura 1991, Hamer and Appleton 1991, Thiery 1991).
The primary historic dispersal mechanisms for the vernal pool crustaceans probably consisted of large scale flooding resulting from winter and spring rains, and dispersal by migratory birds. As a result of widespread flood control and agricultural water diversion projects developed during the twentieth century, large scale flooding is no longer a major form of dispersal for the vernal pool crustaceans. When being dispersed by migratory birds, the eggs of these crustaceans are either ingested (Krapu 1974, Swanson 1974, Driver 1981, Ahl 1991) and/or adhere to the bird's legs and feathers where they are transported to new habitats. Cysts may also be dispersed by a number of other species, such as salamanders, toads, cattle, and humans (Eriksen and Belk 1999).
The vernal pool crustaceans addressed in this proposed rule are generally confined to habitats that are low to moderate in alkalinity and dissolved salts, when compared with other aquatic systems (Ericksen and Belk 1999). Although potentially moderated by soil type, vernal pools are generally unbuffered and exhibit wide fluctuations in pH and dissolved oxygen (Keeley and Zedler 1998). Vernal pool water ion concentrations, such as sodium, potassium, calcium, chlorine, and magnesium, also experience large daily and seasonal variations. These variations are due to the concentration of ions due to evaporation, and the dilution of ions with additional rainfall throughout the wet season (Barclay and Knight 1981). How vernal pool crustacean species adapt to these fluctuations in water chemistry varies. Definitive conclusion on why the species has certain water chemistry habitat preferences is generally unknown due to the anecdotal nature of observations.
Additional information specific to each of the four individual vernal pool crustacean species described in this proposed rule is provided below.
Conservancy Fairy Shrimp
Conservancy fairy shrimp were first described in 1990 by Eng, Belk, and Eriksen. The type specimens were collected in 1982 at Olcott Lake, Solano County, California. Conservancy fairy shrimp are currently known from only eight disjunct areas—Vina plains and vicinity in southern Tehama and northern Butte County; Jepson Prairie in Solano County; Suisun Slough in southern Solano County; Sacramento National Wildlife Refuge in Glenn County; near Caswell Memorial State Park in Stanislaus County; Haystack Mountain Area in eastern Merced County; San Luis National Wildlife Refuge Complex in central Merced County, and the Mutau Flat area in the Los Padres National Forest area of northern Ventura County.
Conservancy fairy shrimp look similar to other fairy shrimp species, but can be distinguished by characteristics of the male second antenna. The second antennae of Conservancy fairy shrimp males have a distal segment which is about 30 percent shorter than the basal segment, and has a tip bent medially about 90 degrees (Eng
et al.
1990). The female brood pouch is tapered at each end, typically extends to abdominal segment 8, and has a terminal opening (Eng
et al.
1990). Males may be from 14 to 27 millimeters (mm) (0.6 to 1.1 in) in length, and females have been measured between 14.5 and 23 mm (0.6 and 0.9 in) long.
Further discussion on the life history and habitat requirements of Conservancy fairy shrimp can be found in the final rule to list this species (59 FR 48136).
Longhorn Fairy Shrimp
Longhorn fairy shrimp were first collected in 1937, but were not formally described until 1990 by Eng, Belk, and Eriksen. The type specimen was collected from a sandstone outcrop pool on the Souza Ranch in Contra Costa County, California. Longhorn fairy shrimp are extremely rare, and are only known from three widely separated locations; the Altamont Pass area in Contra Costa and Alameda counties; the western and northern boundaries of Soda Lake on the Carrizo Plain in San Luis Obispo County; and Kesterson National Wildlife Refuge in the San Joaquin Valley in Merced County. Vernal pool crustacean surveys conducted by Sugnet (1993) found only 3 occurrences of longhorn fairy shrimp out of 3,092 locations surveyed, and Helm (1998) found occurrences of longhorn fairy shrimp in only 9 of 4,008 wetlands sampled.
Longhorn fairy shrimp are distinguished from other fairy shrimp by the male's very long second antennae, which is about twice as long, relative to its body, as the second antennae of other species of
Branchinecta.
Longhorn fairy shrimp antennae range from 6.7 to 10.4 mm (0.3 to 0.4 in) in length (Eriksen and Belk 1999). Females can be recognized by their cylindrical brood pouch, which extends to below abdominal segments 6 or 7. Mature males have been measured between 12 and 21 mm (0.5 to 0.8 in) in length, and females range from 13.3 to 19.8 mm (0.5 to 0.8 in) in length (Eng
et al.
1990).
Further discussion on the life history and habitat requirements of longhorn fairy shrimp can be found in the final rule to list this species (59 FR 48136).
Vernal Pool Fairy Shrimp
Vernal pool fairy shrimp were first described by Eng
et al.
in 1990 from a type specimen that was collected in 1982 at Souza Ranch, Contra Costa County, California. The species occurs in disjunct fragmented habitats distributed across the Central Valley of California from Shasta County to Tulare County and the central and southern coast ranges from northern Solano County to Ventura County, California. Additional disjunct populations have been identified in southern California and in Oregon. In Oregon, the species' distribution is limited to the vicinity of an approximately 82.9 square kilometer (sq km) (32 square mile (sq mi)) area known as the Agate Desert in Jackson County, north of Medford. In southern California the distribution is equally limited with populations occurring in three areas in Riverside County.
Vernal pool fairy shrimp are characterized by the presence and size of several bulges on the male's antenna, and by the female's short, pyriform or pear shaped, brood pouch. Vernal pool fairy shrimp vary in size, ranging from 11 to 25 mm (0.4 to 1.0 in) in length (Eng
et al.
1990).
Vernal pool fairy shrimp are currently found in 27 counties across the Central Valley and coast ranges of California, inland valleys of southern California, and southern Oregon. Although vernal pool fairy shrimp are distributed more widely than most other fairy shrimp species, they are generally uncommon throughout their range, and rarely abundant where they do occur (Eng
et al.
1990, Eriksen and Belk 1999).
Further discussion on the life history and habitat requirements of vernal pool fairy shrimp can be found in the final rule to list this species (59 FR 48136).
Vernal Pool Tadpole Shrimp
Vernal pool tadpole shrimp were initially described by Simon in 1886, and named
Lepidurus packardi.
After subsequent reclassification by Longhurst (1955), the species was given a subspecies status based primarily on the lack of apparent geographic boundaries between
L. apus
and
L. packardi
populations. Lynch (1972)
resurrected
L. packardi
to full species status based on further examination of specimens and this is the currently accepted taxonomic status of vernal pool tadpole shrimp. Vernal pool tadpole shrimp inhabit sites in California's Central Valley and San Francisco Bay area. The geographic range of this species includes disjunct populations found in the Central Valley from Shasta County to northern Tulare County and in the central coast range from Solano County to Alameda County.
Vernal pool tadpole shrimp are distinguished by a large, shield-like carapace, or shell, that covers the anterior half of their body. Vernal pool tadpole shrimp have 30 to 35 pairs of phyllopods, a segmented abdomen, paired cercopods or tail-like appendages, and fused eyes. Vernal pool tadpole shrimp will continue to grow as long as their vernal pool habitats remain inundated, in some cases for six months or longer. They periodically shed their shells, which can often be found along the edges of vernal pools where vernal pool tadpole shrimp occur. Mature vernal pool tadpole shrimp range in size from 15 to 86 mm (0.6 to 3.4 in) in length.
Vernal pool tadpole shrimp have relatively high reproductive rates. Ahl (1991) found that fecundity increases with body size. Large females, greater than 20 mm (0.8 in) carapace length, could deposit as many as 6 clutches, averaging 32 to 61 eggs per clutch, in a single wet season.
Further discussion on the life history and habitat requirements of vernal pool tadpole shrimp can be found in the final rule to list this species (59 FR 48136).
The habitat of the four vernal pool crustaceans is imperiled by a variety of activities, primarily by urban development, water supply and flood control activities, and conversion of land to agricultural use. Habitat loss occurs from direct destruction and modification of pools due to filling, grading, discing, leveling, and other activities, as well as modification of surrounding uplands. Vernal pool crustaceans and their habitat also are threatened by altered flood regimes, degraded water quality, siltation, erosion, grazing, improper burning, military operations, off-road vehicles, pollution, vandalism, road and trail maintenance, and introduction of non-native predators. Further discussion on threats to the vernal pool crustaceans can be found in the final rule to list these species (59 FR 48136).
Vernal Pool Plants Background
The vernal pool plants described in this proposed rule have developed a suite of highly specialized adaptations which allow them to survive in vernal pool habitats. All eleven species are annuals, meaning they germinate, grow, and reproduce within a single year. This allows the vernal pool plants to complete their life cycles during the relatively short inundation and drying periods of their vernal pool habitat.
Another adaptation of vernal pool plants is production of dormant seeds. This adaptation allows vernal pool plants to survive the hot summer months in the soil. The seeds may remain viable in the soil for many years. The number of plants present above ground may fluctuate dramatically from year to year. However, much of the population of these species exists as seeds in the soil. Vernal pool plant seeds generally germinate after winter rains in response to a complex set of environmental cues that are not well understood, but that generally include temperature and soil moisture. Specific germination cues differ greatly among species and are discussed in more detail in the individual species descriptions below. Not all of the dormant seeds will germinate in any given year. This strategy reduces the probability of local extirpation if environmental conditions change, for example if a vernal pool dries up prematurely. This kind of “bet-hedging strategy” has been suggested as a mechanism by which rare species may persist in unpredictable environments (Chesson and Warner 1981, Chesson and Huntly 1989, Ellner and Hairston 1994).
Tolerance to inundation differs greatly among species (Zedler 1987). The zonation of vernal pool plants which forms the characteristic rings of flowers around vernal pools is a result of this differential tolerance to inundation. Species that are the least tolerant to inundation grow along the margins of the pool, while those that can tolerate extended periods of inundation grow in the center of the pools.
Information on the appearance and life history of each of the eleven individual vernal pool plant species described in this proposed rule is provided below.
Butte County Meadowfoam
Butte County meadowfoam (
Limnanthes floccosa
ssp.
californica
) was first collected in 1917 at a site 16 kilometers (km) (10 mi)) north of Chico (Service 1991b), although it was recognized as a separate subspecies at that time. Kalin-Arroyo (1973) determined that Butte County meadowfoam was a distinct taxon and gave it the scientific name
Limnanthes floccosa
ssp.
californica
. The type locality is in Butte County between Chico and Oroville, near the intersection of state Highway 99 and Shippee Road (Kalin-Arroyo 1973).
Butte County meadowfoam is a small annual of the meadowfoam or false mermaid family (Limnanthaceae). It has erect stems less than 25 cm (9.8 in) tall. The stem and leaves are densely pubescent (covered with short hairs). The alternate leaves are pinnately compound (divided into distinct segments which are arranged featherlike on either side of a rachis), up to 8 cm (3.1 in) long, and consist of five to eleven leaflets on a long petiole. A single flower arises in the axil (angle between the base of a leaf and the stem) of each upper leaf. The flowers are white with yellow veins, cup or bowl-shaped, and consist of five petals, five sepals, five pistils (female reproductive structures of a flower), and ten stamens (male reproductive structures of a flower) on a long flower stalk (Kalin-Arroyo 1973, McNeill and Brown 1979, Ornduff 1993b).
Butte County meadowfoam seedlings can tolerate short periods of submergence (Jokerst 1989, Dole and Sun 1992). The seedlings develop into rosettes (clusters of leaves near the ground), which do not begin producing flowering stems immediately (McNeill and Brown 1979, Ritland and Jain 1984). Butte County meadowfoam typically begins flowering in February, reaches peak flowering in March, and may continue into April if conditions are suitable. Nutlets are produced in March and April, and the plants die back by early May (Jokerst 1989, Dole and Sun 1992).
Butte County meadowfoam is predominantly self fertilized (Dole and Sun 1992). Nutlets of Butte County meadowfoam apparently are dispersed by water; they can remain afloat for up to 3 days (Hauptli
et al.
1978).
Limnanthes
taxa that grow in wet sites have larger tubercles than those adapted to dry sites. Hauptli
et al.
(1978) speculated that the tuberculate surface of such nutlets may aid in flotation by trapping air. However, most meadowfoam nutlets are dispersed only short distances. Thus, Butte County meadowfoam nutlets would not be expected to disperse beyond their pool or swale of origin. Birds and livestock are potential sources of long-distance seed dispersal, but specific instances of dispersal have not been documented (Jain 1978).
Butte County meadowfoam has always been confined to the Butte County (Keeler-Wolf
et al.
1998). In her original description, Kalin-Arroyo
(1973) mentioned six collections, including the type locality. Five of those ranged from the original collection site southeast to Oroville, and the sixth was from Table Mountain north of Oroville. However, Jokerst (1983) did not find Butte County meadowfoam on Table Mountain and later suggested that the specimen had been misidentified (Service 1992a).
All 13 of the occurrences described by the CNDDB (2001) had been reported by 1988 (Kalin-Arroyo 1973, McNeill and Brown 1979, Dole 1988, Jokerst 1989). Five were in northern and northeastern Chico near the municipal airport, four (including the type locality) were from the area around Shippee (northwest of Oroville), and three from southeastern Chico. The other occurrence, northeast of the town of Nord, contained only one plant that was of questionable identity (CNDDB 2001). However, the area indicated would be in the same vicinity as the 1917 collection.
Jokerst (1989) identified “north” and “south” races of Butte County meadowfoam in the Chico “sphere of influence” based on morphology. Later, in studies of enzyme systems, Dole and Sun (1992) confirmed that these races differed genetically. They also identified genetically distinct races that they called “northeast” and “southwest,” with the latter referring to the type locality. They found that 96 percent of genetic diversity in Butte County meadowfoam existed among populations and that little variability was evident within populations. Dole and Sun (1992) used mathematical formulas to estimate an average generation time of 2 years for Butte County meadowfoam and to predict that a seed would be transferred between populations only once every 100 to 200 years. Although considerable morphological variability has been observed within populations, it apparently is attributable to differences in environmental response by plants of the same genetic makeup (Jain 1976, Jokerst 1989).
Two occurrences of Butte County meadowfoam have been extirpated, one each in northern and southeastern Chico (Jokerst 1989, Dole and Sun 1992, Service 1992a, CNDDB 2001). Some of the other 11 occurrences have been reduced in extent (CNDDB 2001). The most recent reports are from 1992 and additional losses could have occurred since then.
Sawyer and Keeler-Wolf (1995) mentioned Butte County meadowfoam as only associated with Northern Basalt Flow vernal pools; however, this pool type was likely based on the erroneous Table Mountain occurrence. Butte County meadowfoam occurs primarily in vernal swales and to a lesser extent on the margins of vernal pools (Kalin-Arroyo 1973, Dole 1988, Jokerst 1989, BioSystems Analysis, Inc. 1993, CNDDB 2001). Swales vary in width from narrow channels to broad, pool-like areas (LSA Associates, Inc. 1994). They may connect in branching, tree-like patterns or in net-like patterns around low mounds. Occupied swales are inundated periodically by water from the surrounding uplands, causing the soil to become saturated. However, Butte County meadowfoam does not persist in pools or swales that are inundated for prolonged periods or remain wet during the summer months, nor in drainages where water flows swiftly (Jokerst 1989, Kelley and Associates Environmental Sciences 1993). BioSystems Analysis Inc. (1993) only found it in the wettest swales in 1992 during the drought. Occupied swales are less than 10 cm (3.9 in) deep (LSA Associates, Inc. 1994) and pools are typically less than 30 m (100 ft) long (Jokerst 1989). In both swales and pools, Butte County meadowfoam may grow along the edges or in the bottom (Kalin-Arroyo 1973, Jokerst 1989). In a study of the Shippee area population (BioSystems Analysis, Inc. 1993) Butte County meadowfoam was found growing more often on pool margins than in the bottom of pools but the pattern was reversed in swales, with the plants more often growing in the center. It typically occurs in long, narrow bands in connected swales or on pool margins but can be found in irregular clusters in isolated drainages (Crompton 1993). Butte County meadowfoam has been found occasionally in disturbed areas such as drainage ditches, firebreaks, and graded sites (McNeill and Brown 1979, Jokerst 1989, Kelley and Associates Environmental Sciences 1992, BioSystems Analysis, Inc. 1993, Kelley and Associates Environmental Sciences 1993).
Further discussion on Butte County meadowfoam's life history and habitat characteristics can be found in the final rule to list the species (62 FR 54807).
Contra Costa Goldfields
Greene (1888) first described Contra Costa goldfields, as
Lasthenia conjugens,
from specimens collected near Antioch, California. Hall (1914) later lumped Contra Costa goldfields in with the common species Fremont's goldfields, which at that time was called
Baeria fremontii.
Ferris (1958) proposed the name
Baeria fremontii
var.
conjugens
to recognize the distinctiveness of
L. conjugens.
Finally, Ornduff (1966) restored Greene's original name and rank, returning this species to the genus
Lasthenia.
Contra Costa goldfields is a showy spring annual in the aster family (Asteraceae). Its stems are 10 to 30 cm (4 to 12 in) tall, somewhat fleshy, and usually are branched. The leaves are opposite and narrow; the lower leaves are entire, but stem leaves have one or two pairs of narrow lobes. The daisy-like flower heads are solitary (Greene 1888, Ornduff 1993a).
As a vernal pool annual, seeds of Contra Costa goldfields would be expected to germinate in response to autumn rains, with the plants maturing in a single growing season, setting seed, and dying back during the summer. However, detailed research on the life cycle has not been conducted. Contra Costa goldfields flower from March through June (Ornduff 1966, Ornduff 1979, Skinner and Pavlik 1994). The flowers are self-incompatible (Crawford and Ornduff 1989). Insect visitors to flowers of
Lasthenia
belong to five orders—Coleoptera, Diptera, Hemiptera (true bugs), Hymenoptera (ants, bees and wasps), and Lepidoptera (butterflies and moths) (Thorp and Leong 1998). Most of these insects are generalist pollinators. Some
Lasthenia
are pollinated by specialist solitary bees (family Andrenidae); including two bee species in the subgenus
Diandrena
(
Andrena submoesta
and
A.
puthua
) and five or six species in the subgenus Hesperandrena (
Andrena baeriae, A. duboisi, A. lativentris,
and two or three undescribed species) (Thorp and Leong 1998). The extent to which pollination of Contra Costa goldfields depends on host-specific bees or more generalist pollinators is currently unknown.
Seed dispersal mechanisms in Contra Costa goldfields are unknown. However, the lack of a pappus or even hairs on the achenes makes wind dispersal unlikely (Ornduff 1976). Seed longevity, survival rates, fecundity, and other demographic parameters have not been investigated. However, as with other vernal pool annuals, population sizes have been observed to vary by up to four orders of magnitude from year to year (CNDDB 2001).
By far the greatest concentration of this species is in Solano County where Contra Costa goldfields are found in the area east and south of the City of Fairfield. Other areas that support populations of this species include the central coast between Monterey and Alameda counties, including Fort Ord in Monterey County, San Francisco Bay National Wildlife Refuge, and near Fremont, in Alameda County. The Santa Barbara County occurrence has probably been lost due to habitat alteration
(CNDDB 2001). Contra Costa goldfields also occurs near Manchester in Mendocino County, and at Suscol Ridge in Napa County. Another Napa County site, Milliken Canyon, contained only a single plant in 1987 and may or may not be still in existence (CNDDB 2001). The other existing occurrence is near Rodeo in Contra Costa County (CNDDB 2001).
Further discussion on Contra Costa goldfields' life history and habitat characteristics can be found in the final rule to list the species (62 FR 33037).
Hoover's spurge
Hoover's spurge (
Chamaesyce hooveri
) was originally named
Euphorbia hooveri
based on a specimen collected by Hoover in Yettem, Tulare County (Wheeler 1940). Koutnik (1985) placed the species in the genus
Chamaesyce
as
Chamaesyce hooveri.
Hoover's spurge is an annual herb of the spurge family (Euphorbiaceae). Hoover's spurge trails along the ground, forming gray-green mats 5 to 100 cm (2.0 to 39.4 in) in diameter (Broyles 1987, Stone
et al.
1988). The stems are hairless and contain milky sap. The tiny (2 to 5 mm (0.08 to 0.20 in)) leaves are opposite, rounded to kidney-shaped, with an asymmetric base and a toothed margin. In the genus
Chamaesyce,
the structures that appear to be flowers actually are groups of flowers; each group is referred to as a cyathium (Koutnik 1993).
Few details of the life history of Hoover's spurge are known. Seeds of Hoover's spurge germinate after water evaporates from the pools; the plants cannot grow in standing water (Alexander and Schlising 1997). The indeterminate growth pattern allows the plants to continue growing as long as sufficient moisture is available. The proportion of seedlings surviving to reproduction has not been documented; in years of below normal rainfall, seedling survival was characterized as “low” (Stone
et al.
1988). The phenology (timing of various stages in the life cycle of a plant) varies among years and among sites, even for those populations in close proximity (Stone
et al.
1988). Populations in Merced and Tulare counties typically flower from late May through July, whereas those in Stanislaus County and the Sacramento Valley flower from mid-June into October (Alexander and Schlising 1997, CNDDB 2001, J. Silveira USFWS pers. comm.). Seed set apparently begins soon after flowering. Seed production has not been quantified or studied in relation to environmental factors, but Stone
et al.
(1988) reported that large plants may produce several hundred seeds. Horned larks (
Eremophila alpestris
) have been observed eating seeds of Hoover's spurge and thus may assist in seed dispersal (Alexander and Schlising 1997).
Demographic data suggest that seeds of Hoover's spurge can remain dormant until the appropriate temperature and moisture conditions occur. This is evident from the fact that plants can be absent from a given pool for up to four years and then reappear in substantial numbers. Although certain years appear to be more favorable for Hoover's spurge than others, population trends vary from pool to pool, even within the same year in the same area. Moreover, a particular year may be favorable for Hoover's spurge at one site and unfavorable at another. For example, Hoover's spurge was extremely abundant on the Vina Plains Preserve in 1995, but reached a 7-year low at Sacramento National Wildlife Refuge that year. Five occurrences of Hoover's spurge have numbered 5,000 or more plants at their maximum size. Four of those five occur on the Vina Plains, and the other occurs in Tulare County (Stone
et al.
1988, CNDDB 2001).
Hoover's spurge probably is pollinated by insects. Related species in the spurge family are pollinated by flies (Heywood 1978, Stone
et al.
1988). Also, glands on the plant produce nectar (Wheeler 1941), which is attractive to insects. Beetles, flies, bees and wasps, and butterflies and moths (order Lepidoptera) have been observed visiting the flowers of Hoover's spurge and may potentially serve as pollinators (Stone
et al.
1988, Alexander and Schlising 1997). Related species in the genus
Euphorbia
typically are cross-pollinated because the female flowers on each plant mature before the male (Heywood 1978, Stone
et al.
1988), which may or may not be the case for Hoover's spurge.
For decades, Hoover's spurge was known from only three localities—near Yettem and Visalia in Tulare County, and near Vina in Tehama County. Collections were made from these three areas in the late 1930's and early 1940's (Wheeler 1941, Munz and Keck 1959, Stone
et al.
1988). From 1974 through 1987, 21 additional occurrences of Hoover's spurge were reported. The majority of these (15) were in Tehama County. One to three occurrences were discovered during this period in each of Butte, Merced, Stanislaus, and Tulare counties (Stone
et al.
1988, CNDDB 2001).
The CNDDB (2001) now includes 30 occurrences of Hoover's spurge. In addition to those known historically, six occurrences were discovered in 1992 (three each in Glenn and Tulare counties). Of the 30 occurrences, one each in Tehama and Tulare counties are classified as extirpated; two others, in Butte and Tehama counties, are “possibly extirpated” because this species was not observed for two consecutive years (Stone
et al.
1988, CNDDB 2001). Of the 26 occurrences presumed to be extant, only 12 have been observed within the past decade (CNDDB 2001).
The main area of concentration for Hoover's spurge is within the northeastern Sacramento Valley. The Vina Plains of Tehama and Butte counties contains 14 (53.8 percent) of the 26 extant occurrences for Hoover's spurge (CNDDB 2001) in an area approximately 91 sq km (35 sq mi) in extent (Stone
et al.
1988). One other site in the same region is near Chico in Butte County. Seven of the extant occurrences are in Southern Sierra Foothills Vernal Pool Region, including five in the Visalia-Yettem area of Tulare County and two in the Hickman-La Grange area of Stanislaus County. Three other occurrences are on the Sacramento National Wildlife Refuge in Glenn County, which is in the Solano-Colusa Vernal Pool Region. The one other extant occurrence is on the Bert Crane Ranch in Merced County, which is within the San Joaquin Valley Vernal Pool Region (Keeler-Wolf
et al.
1998, CNDDB 2001).
Further discussion on Hoover's spurge's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14351).
Succulent Owl's-Clover
Succulent (or fleshy) owl's-clover was first described by Hoover (1936a) as
Orthocarpus campestris
var.
succulentus.
The type specimen had been collected at Ryer, in Merced County. Hoover (1968) subsequently raised succulent owl's-clover to the rank of species and assigned it the name
Orthocarpus succulentus.
Chuang and Heckard (1991) reconsidered the taxonomy of
Orthocarpus
and related genera. Based on floral morphology (external structure or form), seed morphology, and chromosome number, they transferred many species into the genus
Castilleja.
Furthermore, they determined that the appropriate rank for succulent owl's-clover was as a subspecies of
Castilleja campestris
(field owl's-clover). The scientific name currently assigned to the plant is
Castilleja campestris
ssp.
succulenta
(Chuang and Heckard 1991).
Succulent owl's-clover is a hemiparasitic (partly parasitic) annual herb belonging to the snapdragon family (Scrophulariaceae). It has erect or
decumbent stems up to 30 cm (11.8 in) long. The stems are usually unbranched and without hairs. The leaves at the base of the stem are small and scalelike, whereas those on the upper stem are lance-shaped, not lobed, thick, fleshy, brittle, and easily broken. The bracts (leaf-like structures in the flowering structure) are green, similar to but shorter than the upper leaves, and longer than the flowers. Overall, the inflorescence (entire flowering structure of a plant) may occupy as much as half of the plant's height (Hoover 1936a, Hoover 1937, Hoover 1968, Chuang and Heckard 1991, Chuang and Heckard 1993).
As with many related species, succulent owl's-clover is a hemiparasite, meaning that it obtains water and nutrients by forming root grafts with other host plants but manufactures its own food through photosynthesis (Chuang and Heckard 1991). Research on hemiparasitism has focused on related species of
Castilleja
, but not specifically on succulent owl's-clover. Many different plants can serve as hosts for a single species or even a single individual of
Castilleja
. Seeds do not require the presence of a host to germinate, and form root connections only after reaching the seedling stage. Some seedlings can survive to maturity without attaching to a host's roots, but in general reproduction is enhanced by root connections (Atsatt and Strong 1970).
The conditions necessary for germination of succulent owl's-clover seeds have not been studied, nor has the timing of seed germination been documented. Flowering occurs in April and May (Skinner and Pavlik 1994). Although many related taxa of
Castilleja
are pollinated by generalist bees (Superfamily Apoidea) (Chuang and Heckard 1991), succulent owl's-clover is thought to be self-pollinating. Among close relatives that do not require insect pollinators, flower structure and timing of stigma receptivity maximize the chances for self-fertilization and seed set. Even so, insects may transfer some pollen among individual plants and species occurring in the same area. Self-pollinating species of
Castilleja
typically occur as widely scattered individuals, rather than in dense colonies (Atsatt 1970). Succulent owl's-clover follows this pattern in part, often occurring in many pools within a complex but with fewer than 100 plants per pool. However, succulent owl's-clover also may occur in large populations within a single pool (California Natural Diversity Data Base (CNDDB) 2001). Little is known about the demography of succulent owl's-clover, although population size can fluctuate greatly from year to year. In the few populations where population size was reported for more than 1 year, fluctuations up to two orders of magnitude were noted (CNDDB 2001).
Succulent owl's-clover is known from vernal pool habitats along the Southern Sierra Foothills ranging from Madera County to a disjunct occurrence in northern San Joaquin County. The highest density of occurrences of succulent owl's-clover occurs in Merced County, but the species is also known from Fresno, Madera, Stanislaus, and San Joaquin counties.
Further discussion on succulent owl's-clover life history and habitat characteristics can be found in the final rule to list the species (62 FR 14351).
Orcuttieae Tribe
Colusa grass, hairy Orcutt grass, Solano grass, Greene's tuctoria, Sacramento Valley Orcutt grass, San Joaquin Valley Orcutt grass, and slender Orcutt grass belong to the tribe Orcuttieae in the grass family, Poaceae (Reeder 1965). Many life history characteristics are common to all members of the Orcuttieae. All are wind pollinated, but pollen probably is not carried long distances between populations (Griggs 1980, Griggs 1981, Griggs and Jain 1983). Local seed dispersal is by water, which breaks up the inflorescence (Reeder 1965, Crampton 1976, Griggs 1980, Griggs 1981). Long distance dispersal is unlikely (Service 1985c) but seed may have been carried occasionally by waterfowl (family Anatidae), tule elk (
Cervus elaphus nannoides
), or pronghorn (
Antilocapra americana
) in historical times (Griggs 1980). The seeds can remain dormant for an undetermined length of time, but at least for 3 or 4 years, and germinate underwater after they have been immersed for prolonged periods (Crampton 1976, Griggs 1980, Keeley 1998a). Unlike typical terrestrial grasses that grow in the uplands surrounding vernal pools, members of the Orcuttieae flower during the summer months (Keeley 1998a).
All members of the Orcuttieae tribe have large soil seed banks that may often be 50 times or more larger in numbers than the above ground population in any given year. In general, years of above average rainfall promote larger populations of Orcuttieae, but population responses vary by pool and by species (Griggs 1980, Griggs and Jain 1983). Population sizes have been observed to vary by one to four orders of magnitude among successive years and to return to previous levels even after 3 to 5 consecutive years when no mature plants were present (Griggs 1980, Griggs and Jain 1983, Holland 1987). Thus, many years of observation are necessary to determine whether a population is stable or declining.
All members of the Orcuttieae are endemic to vernal pools. Although the various species have been found in pools ranging widely in size, the vast majority occur in pools of 0.01 ha (0.03 ac) to 10 ha (24.7 ac) (Stone
et al.
1988). Larger pools retain water until May or June, creating optimal conditions for Orcuttieae (Crampton 1959, Crampton 1976, Griggs 1981, Griggs and Jain 1983). Orcuttieae occur in patches within the pools that are essentially devoid of other plant species (Crampton 1959, Crampton 1976). Typically, plants near the center of a pool grow larger and produce more spikelets than those near the margins, but patterns vary depending on individual pool characteristics and seasonal weather conditions (Griggs 1980).
The specific life history requirements and distribution of each of the seven Orcuttieae species are provided below.
Colusa Grass
Colusa grass (
Neostapfia colusana
) was first described by Davy (1898), and given the Latin name
Stapfia colusana
. He had collected the type specimen near the town of Princeton in Colusa County. Davy soon realized that the name
Stapfia
had already been assigned to a genus of green algae and therefore changed the scientific name of Colusa grass to
Neostapfia colusana
(Davy 1899). Two other taxonomists proposed alternate Latin names for the genus in the same year, but neither is accepted today. No other species of
Neostapfia
are known (Reeder 1982, Reeder 1993).
Unlike terrestrial grasses, Colusa grass has pith filled stems, lacks distinct leaf sheaths and ligules, and produces exudate (aromatic, sticky fluid discharged from the plant surface). Colusa grass stems and inflorescence (flower cluster) differs from other members of the Orcuttieae. The plant is pale green when young (Davy 1898) but becomes brownish as the exudate darkens (Reeder 1982, Reeder 1993).
Existing populations of Colusa grass are concentrated northeast of the city of Merced in Merced County and east of Hickman in Stanislaus County. Colusa grass also occurs in central Merced County, in southeastern Yolo County, and in central Solano County (Stone
et al.
1988, Keeler-Wolf
et al.
1998, CNDDB 2001). This species has been extirpated from Colusa County (CNDDB 2001).
In the 50 years after its initial discovery (Davy 1898), Colusa grass was reported from only three sites other than the type locality; these were in Merced and Stanislaus counties. By the mid-1970's Colusa grass had been reported from a total of 11 sites in Colusa, Merced, Solano, and Stanislaus counties (Hoover 1936b, Hoover 1940, Crampton 1959, Medeiros 1976, Reeder 1982). During the 1980's, many new populations of Colusa grass were located during extensive surveys. As of 1989, 40 occurrences were extant and 11 already had been extirpated. Of the 51 occurrences known up to that point, 26 were in Merced County, 22 were in Stanislaus County, 2 were in Solano County, and one was in Colusa County (Stone
et al.
1988, CNDDB 2001). Currently, the CNDDB (2001) considers 48 occurrences of Colusa grass to be “presumed extant” and 11 others as known or possibly extirpated.
Further discussion on Colusa grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
Greene's Tuctoria
Greene's tuctoria (
Tuctoria greenei
) was originally assigned its name by Vasey (1891) as
Orcuttia greenei
. Greene had collected the type specimen in 1890 “on moist plains of the upper Sacramento, near Chico, California” (Vasey 1891), presumably in Butte County (Hoover 1941, Crampton 1959). Citing differences in lemma morphology, arrangement of the spikelets, and other differences, Reeder (1982) segregated the genus
Tuctoria
from
Orcuttia
and created the new scientific name
Tuctoria greenei
for this species.
Greene's tuctoria is an erect to low growing annual with fragile stems that easily break apart at the nodes, which are often purplish. The leaves are flat and curve outward and the plants are sparsely hairy. The inflorescence is crowded near the tip with the lower spikelets more or less separated. Optimum germination of Greene's tuctoria seed occurs when the seed is exposed to light and anaerobic (lacking oxygen) conditions after stratification (Keeley 1988). Germination occurs several months after initial inundation (Keeley 1998a).
Tuctoria
seedlings do not develop floating juvenile leaves, as does
Orcuttia
(Griggs 1980, Keeley 1998a). The adult plants apparently do not tolerate inundation; all five Greene's tuctoria plants in a Glenn County pool died when the pool refilled during late spring rains in 1996 (Silveira
in litt.
1997). Greene's tuctoria flowers from May to July (Skinner and Pavlik 1994), with peak flowering in June and July (Griggs 1981, Broyles 1987).
As with other vernal pool annuals, population size in Greene's tuctoria can vary enormously from year to year, and populations that have no visible plants one year can reappear in large numbers in later years. Population fluctuations may be due to annual variations in weather, particularly rainfall, to changes in management, or to a combination of the two. Such fluctuations were observed at scattered sites in Butte and Tehama counties during the 1970's (Griggs 1980, Griggs and Jain 1983) and at Sacramento National Wildlife Refuge, where the population in the single occupied pool ranged from zero to 60 plants between 1994 and 1999 (Silveira
in litt.
2000). Fluctuations of as much as three orders of magnitude were documented on the Vina Plains Preserve during the 1980's and 1990's (Alexander and Schlising 1997)
After its discovery in Butte County in 1890, Greene's tuctoria was not seen again for over 40 years. During extensive surveys in the late 1930's, Hoover (1937, 1941) found the species at sites in Fresno, Madera, Merced, San Joaquin, Stanislaus, Tehama, and Tulare counties. In fact, he described it as the most common of all
Orcuttia
species, with which it was classified at the time. By the end of the 1980's, Greene's tuctoria had been reported from a total of 36 occurrences in the same 8 counties (Stone
et al.
1988, CNDDB 2001).
Three additional occurrences of Greene's tuctoria have been discovered during the past decade, bringing the reported total to 39 occurrences (Oswald and Silveira 1995, CNDDB 2001). However, 19 of the historical occurrences apparently have been extirpated. The other 20 occurrences are presumed to be still in existence, although 6 of those have not been verified for more than a decade (Alexander and Schlising 1997, CNDDB 2001).
Sixty percent of the extant occurrences of Greene's tuctoria are in the Vina Plains area of Tehama and Butte counties. Eastern Merced County has about 30 percent of the known occurrences. Other occurrences are located in Glenn (Oswald and Silveira 1995) and Shasta counties (CNDDB 2001). Greene's tuctoria has been extirpated from Fresno, Madera, San Joaquin, Stanislaus, and Tulare counties (Stone
et al.
1988, Skinner and Pavlik 1994, CNDDB 2001).
Further discussion on Greene's tuctoria's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
Hairy Orcutt Grass
Hoover (1941) described hairy Orcutt grass as (
Orcuttia pilosa
) from specimens he collected in Stanislaus County, “12 miles east of Waterford” in 1937. Hairy Orcutt grass grows in tufts consisting of numerous stems. The stems are decumbent (laying on the ground with the tip turned upward) or erect and branch from only the lower nodes. Almost the entire plant is pilose or hairy, giving it a grayish appearance. The spikelets near the tip of the inflorescence are crowded together, whereas those near the base are more widely spaced.
Griggs (1974 cited in Stone
et al.
1988) found that stratification followed by temperatures of 15 to 32°C (59 to 90°F) was necessary for seed germination in hairy Orcutt grass. Flowering period for the plant is mid-April through July. Seed production has not been studied extensively in hairy Orcutt grass, but Griggs and Jain (1983) did note that one individual produced more than 10,000 seeds. Although the predominant pollination agent for all Orcutt grasses is wind, native bees (Halictidae) have been observed visiting the inflorescence of hairy Orcutt grass to gather pollen (Griggs 1974 cited in Stone
et al.
1988).
Like other vernal pool annuals, the size of hairy Orcutt grass populations fluctuates dramatically from year to year. Population sizes have varied by as much as four orders of magnitude over time (Griggs 1980, Griggs and Jain 1983, Alexander and Schlising 1997). In fact, two populations that had no visible plants for three successive years exceeded 10,000 plants in the fourth year (Griggs 1980, Griggs and Jain 1983).
Hairy Orcutt grass is known from sites in the southern portion of the Sacramento Valley and the southern Sierra foothills (Keeler-Wolf
et al.
1998). The species has been found in Tehama, Stanislaus, Madera, and Merced counties (Hoover 1941, Crampton 1959, Reeder 1982, Stone
et al.
1988, CNDDB 2001). Hairy Orcutt grass also was collected in Glenn County, in 1937 (CNDDB 2001); the specimen has since been lost but may have been misidentified as California Orcutt grass (Silveira
in litt.
2000). During the late 1980's, Stone
et al.
(1988) determined that 12 historical occurrences had been extirpated but they and others discovered three additional populations in Madera, Stanislaus, and Tehama counties. One other occurrence from Madera County was previously considered to be hairy Orcutt grass and is listed as such in the CNDDB (2001); however, this population since has been
identified as San Joaquin Valley Orcutt grass (Stone
in litt.
1992).
Within the past decade, hairy Orcutt grass has been discovered in additional areas in Glenn, Madera, and Tehama counties (CNDDB 2001). Hairy Orcutt grass has also been discovered in another pool at the Vina Plains Preserve in Tehama County (Alexander and Schlising 1997). Of the 38 element occurrences listed by the CNDDB (2001), not counting the misidentified population of San Joaquin Valley Orcutt grass, 24 natural occurrences are presumed to be still in existence. Nineteen of those occurrences have been confirmed as existing within the past decade (CNDDB 2001).
Further discussion on hairy Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
Sacramento Orcutt Grass
Hoover (1941) first described Sacramento Orcutt grass (
Orcuttia viscida
) as
Orcuttia californica
var.
viscida
based on the type specimen he collected from “7 miles south of Folsom” in Sacramento County. Reeder (1980) determined that the differences in morphology, seed size, and chromosome number were sufficient grounds to elevate Sacramento Orcutt grass to the species level as
Orcuttia viscida.
In basic form, Sacramento Orcutt grass resembles other members of the tribe and genus. Although all members of the Orcuttieae produce exudate, Sacramento Orcutt grass is particularly viscid even when young. The plants are densely tufted, bluish green, and covered with hairs. The stems are erect or spreading, 3 to 10 cm (1 to 4 in) long, and do not branch. The inflorescence occupies the upper one third to one half of the stem and consists of between 5 and 15 spikelets. The spikelets are closely spaced, and although distichous (arranged in two opposing rows) are oriented towards one side of the stem.
Sacramento Orcutt grass flowers in May and June (Griggs 1977, Skinner and Pavlik 1994, Cochrane
in litt.
1995a) and sets seed in June and July (Holland 1987). Seeds likely do not disperse far under natural conditions. In a 6-year period, an experimental population spread at most 3 m (10 ft) from the seed source, and 95 percent of plants were within 30 cm (12 in) of the source (Holland
in litt.
1986). A demographic study conducted from 1974 to 1978 (Griggs 1980, Griggs and Jain 1983) indicated that Sacramento Orcutt grass produced an average of 500 seeds per plant. At one site in 1978, 88 percent of plants survived to maturity. The size of the seed bank stored in the soil was approximately 44 times as great as the population of growing plants (Griggs 1980, Griggs and Jain 1983). The number of plants varies with rainfall. Large numbers of plants grow only in years when seasonal rainfall exceeds 40 cm (16 in), particularly when heavy rains begin in November and continue through the end of April (Holland 1987). This species is less likely to germinate in years of below normal precipitation than are other members of the tribe (Griggs 1980, Griggs and Jain 1983).
Sacramento Orcutt grass is endemic to the southeastern Sacramento Valley (Keeler-Wolf
et al.
1998) and always has been restricted to Sacramento County. The earliest collection was from 1936 near Phoenix Field. Three other occurrences documented in 1941 and 1958 extended the range north to Orangevale and south to near Sloughhouse. Sacramento Orcutt grass was introduced to Phoenix Park, in Sacramento County, in 1978. Three additional natural occurrences were discovered in the late 1980's, including one in extreme southeastern Sacramento County near State Highway 104. Thus, by 1990 this species was known from a total of seven natural occurrences and one introduction (Stone
et al.
1988, CNDDB 2001).
Within the past decade, Sacramento Orcutt grass has been discovered at one new site in Sacramento County, within the previously known range. However, one entire occurrence and a portion of another have been extirpated. Thus, eight of the nine occurrences are still in existence. Five occurrences, comprising more than 70 percent of the occupied habitat, are concentrated into a single small area east of Mather Field. Two other occurrences are adjacent to each other-Phoenix Field Ecological Reserve and the introduced population at Phoenix Park. The eighth existing occurrence is near Rancho Seco Lake (Stone
et al.
1988, Cochrane
in litt.
1995a, CNDDB 2001).
Further discussion on Sacramento Orcutt grass life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
San Joaquin Valley Orcutt Grass
Hoover (1936b) described San Joaquin Valley Orcutt grass (
Orcuttia inaequalis
) based on a collection from “Montpellier [sic], Stanislaus County.” Hoover (1941) subsequently reduced this taxon to a variety of
Orcuttia californica,
using the combination
Orcuttia californica
var.
inaequalis.
Based on differences in morphology, seed size, and chromosome number, Reeder (1980) restored the taxon to species status.
Mature plants of San Joaquin Valley Orcutt grass grow in tufts of several erect stems. The plant is grayish-green due to the long hairs on the stem and leaves and produces exudate.
Orcuttia
plants grow underwater for 3 months or more and have evolved specific adaptations for aquatic growth (Keeley 1998a).
The earliest collection of San Joaquin Valley Orcutt grass was made in 1927 from the Fresno-Madera County border near Lanes Bridge (CNDDB 2001). Hoover (1941) mentioned collections from eight sites in Fresno, Madera, Merced, Stanislaus, and Tulare counties. A total of 20 occurrences had been reported by the mid 1970's, all in the same five counties (Crampton 1959, CNDDB 2001), but none remained as of the late 1970's (Griggs 1980, Griggs and Jain 1983). However, since that time San Joaquin Valley Orcutt grass has been discovered in Merced, Madera, and Fresno counties, and recently additional occurrences of San Joaquin Valley Orcutt grass have been found, including sites in Tulare County. Of the 47 occurrences of San Joaquin Valley Orcutt grass reported in CNDDB (2001), 27 are presumed to be still in existence; 17 are certainly extirpated and 3 others are possibly extirpated because the habitat has been modified (CNDDB 2001). However, only 12 of the occurrences presumed still in existence have been revisited within the past decade, so even the most recent information is outdated. This species has been completely extirpated from Stanislaus County but remains in Fresno, Madera, Merced, and Tulare counties (Stone
et al.
1988, Skinner and Pavlik 1994, CNDDB 2001).
Further discussion on San Joaquin Valley Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
Slender Orcutt Grass
Slender Orcutt grass (
Orcuttia tenuis
) was first named by Hitchcock (1934). The type specimen of slender Orcutt grass was collected in Goose Valley, Shasta County, in 1912. Slender Orcutt grass grows as single stems or in small tufts consisting of a few stems. The plants are sparsely hairy and branch only from the upper half of the stem. Although the stems typically are erect, they may become decumbent if many branches form near the stem tip (Reeder 1982). The inflorescence comprises more than half of the plant's height, and the spikelets are more or less evenly spaced throughout the inflorescence.
Optimal germination of slender Orcutt grass is achieved through stratification
followed by warm days and mild nights (Griggs 1974 in Stone
et al.
1988). Peak flowering of this species typically occurs in May in the Central Valley (Griggs 1981, Reeder 1982) but not until June or July on the Modoc Plateau (Schoolcraft
in litt.
2000). Unlike hairy Orcutt grass and Greene's tuctoria, slender Orcutt grass is not likely to die when pools are flooded by late spring or summer rains (Griggs 1980, Griggs and Jain 1983). Conversely, drought has been known to cause 100 percent mortality (Griggs 1980, Griggs and Jain 1983).
Similar to other vernal pool annuals, slender Orcutt grass populations can vary greatly in size from year to year. Fluctuations of up to four orders of magnitude have been documented in Lake and Shasta counties (Griggs 1980, Griggs and Jain 1983). At the Vina Plains Preserve, the single population ranged in size from 1,000 to 147,700 individuals during the five times it was reported over a 13 year period (Stone
et al.
1988, Alexander and Schlising 1997). However, slender Orcutt grass populations do not always fluctuate in size. Among five populations of slender Orcutt grass that Griggs tracked from 1973 to 1979, two in the Dales area remained at the same order of magnitude for the entire period. None of the other five species of Orcuttieae included in the study remained stable for the full 7 years (Griggs 1980, Griggs and Jain 1983).
By the mid 1980s, slender Orcutt grass was known from only 18 localities in Lake, Sacramento, Shasta, and Tehama counties (Reeder 1982, Stone
et al.
1988). During the late 1980s, Stone
et al.
(1988) and others (CNDDB 2001) discovered 34 additional occurrences of slender Orcutt grass. Slender Orcutt grass was found primarily in Tehama County, in the vicinity of Dales and on the Vina Plains. The species was also found in the Stillwater and Millville Plains of Shasta County, and at additional sites in Shasta, Siskiyou, Lake, and Sacramento counties (Griggs and Jain 1983, Stone
et al.
1988, CNDDB 2001). During the past decade, 27 new occurrences of slender Orcutt grass have been reported. In addition to the counties where it was reported historically, slender Orcutt grass is now known from Lassen and Plumas counties. The extirpated occurrences of slender Orcutt grass were near Reading Airport and Stillwater Plains in Shasta County and additional possibly extirpated occurrences were near Goose Valley and Battle Creek in Tehama and Shasta counties.
Further discussion on slender Orcutt grass's life history and habitat characteristics can be found in the final rule to list the species (62 FR 14338).
Solano Grass
Solano grass (
Tuctoria mucronata
) was originally described under the name
Orcuttia mucronata
based on specimens collected “12 miles due south of Dixon, Solano County” (Crampton 1959, p. 108). Reeder (1982) transferred this species to a new genus,
Tuctoria
, resulting in the currently accepted name
Tuctoria mucronata.
Solano grass is grayish-green, pilose, and sticky. The tufted stems are decumbent and do not branch. The long leaves are rolled inward and have pointed tips. The base of the inflorescence is partially hidden by the uppermost leaves. As is characteristic of the genus, the spikelets are arranged in a spiral; the spikelets in the inflorescence of Solano grass are crowded together.
Solano grass typically flowers in June and sets seed during July (Holland 1987). The demography of Solano grass has not been investigated in detail. Annual estimates or counts at Olcott Lake (Holland 1987, CNDDB 2001) indicated that population sizes for this species fluctuate dramatically from year to year, as do other members of the Orcuttieae. Solano grass was not observed at Olcott Lake from 1976 through 1980, then reappeared in 1981 (Holland 1987), indicating that viable seeds can persist in the soil for a minimum of 5 years. Apparently both drought years and years of excessively high rainfall are unfavorable for Solano grass; the largest populations were observed after seasons of 45 to 60 cm (17.7 to 23.6 in) of precipitation (Holland 1987).
Prior to 1985, Solano grass was known only from Olcott Lake in Solano County, which is believed to be the type locality (Crampton 1959, CNDDB 2001). A second occurrence was discovered in 1985 approximately 4 km (2.5 mi) southwest of Olcott Lake (CNDDB 2001). Solano grass is presumed to remain at the type locality, although only four individual plants have been found within the last decade, all in 1993 (CNDDB 2001). The other Solano County site is still in existence. A third occurrence, comprising the largest population known, was discovered in 1993 on a Department of Defense (DOD) communications facility in Yolo County (CNDDB 2001).
Further discussion on Solano grass's life history and habitat characteristics can be found in the Delta Green Ground Beetle and Solano Grass Recovery Plan (Service 1985c).
The vernal pool plants are threatened by habitat loss and degradation due to urbanization, agricultural land conversion, off road vehicle use, flood control projects, highway projects, altered hydrology, landfill projects, and competition from weedy nonnative plants. The habitat of these species has been reduced and fragmented throughout their respective ranges as vernal pools continue to be eliminated. Further discussion on threats to the vernal pool plants can be found in the final rules to list these species (62 FR 34029, 62 FR 14338, 57 FR 24192, 43 FR 44810) and in the criteria section of this proposed rule.
Previous Federal Action (Vernal Pool Crustaceans)
Ms. Roxanne Bittman petitioned us to list Conservancy fairy shrimp, longhorn fairy shrimp, vernal pool fairy shrimp, and California linderiella (
Linderiella occidentalis
) as endangered species on November 19, 1990. Ms. Dee Warneycia petitioned us to list vernal pool tadpole shrimp as an endangered species on April 28, 1991. On May 8, 1992, we published a proposed rule in the
Federal Register
(57 FR 19856) to list the four fairy shrimp and vernal pool tadpole shrimp as endangered. On September 19, 1994, we published a final rule in the
Federal Register
(59 FR 48136) determining endangered status for Conservancy fairy shrimp, longhorn fairy shrimp and vernal pool tadpole shrimp and threatened status for vernal pool fairy shrimp. We withdrew the California linderiella as a species proposed for listing based on additional information received during the public review and comment period indicating that during the review period this species was more abundant than previously known.
On April 17, 1995, the Building Industry Association of Superior California (BIAC) and Marvin L.Oates (Plaintiffs) filed a lawsuit in Federal District Court for the District of Columbia against Bruce Babbit (Secretary, Department of the Interior)
et al.
(Defendants) and Environmental Defense Center and Butte Environmental Council (Defendent-Intervenors) arguing that the listing of four vernal pool crustaceans (Conservancy fairy shrimp, longhorn fairy shrimp, vernal pool fairy shrimp, and vernal pool tadpole shrimp) violated the Act, the Administrative Procedures Act, the Fifth Amendment, the Tenth Amendment, and the Commerce Clause of the United States Constitution (
Building Industry Association of Superior California, et al.
v.
Babbit et al.
, CIV 95-0726 PLF). On
July 25, 1997, the district court granted the defendant's motion for summary judgement on all aspects except the decision not to designate critical habitat. The plaintiffs later amended their complaint to drop the claim relating to the designation of critical habitat and the district court vacated its ruling regarding this matter. On April 12, 2000, the Butte Environmental Council filed suit, alleging that our failure to establish critical habitat for the four vernal pool crustaceans violated the Endangered Species Act and the Administrative Procedures Act (
Butte Environmental Council
v.
White
CIV S-00-797 WES GGH). On February 9, 2001, the U.S. District Court for the Eastern District of California granted the plaintiff's motion for summary judgement and required the defendants, to the maximum extent prudent and determinable, to designate critical habitat for the four vernal pool crustaceans within six months.
On July 23, 2001, the district court approved a settlement agreement between the parties which extended the deadline for designation of critical habitat to August 15, 2002. As a condition of the settlement, we agreed to also designate critical habitat, to the maximum extent prudent and determinable, for the eleven vernal pool plants addressed in this proposed rule by the same date.
Previous Federal Action (Vernal Pool Plants)
Section 12 of the Act directed the Secretary of the Smithsonian Institution to prepare a report on plant species which were or might become endangered or threatened. The resulting report, dated January 9, 1975, reviewed the status of 3,100 vascular plants. The report categorized as endangered six of the eleven vernal pool plants under consideration here, and categorized two others as threatened. The six plants considered endangered were hairy Orcutt grass, Sacramento Orcutt grass, slender Orcutt grass, Colusa grass, San Joaquin Valley Orcutt grass, and succulent owl's clover. The two threatened plants were Contra Costa goldfields and Hoover's spurge. On July 1, 1975, the Director of the Department of the Interior published a notice (40 FR 27823) accepting the Smithsonian Institution's report as a listing petition within the context of section 4(c)(2) of the Act (petition provisions are now found in section 4(b)(3)), and of his intention to review the status of the plants covered by the report. On June 16, 1976, based on both the Smithsonian report and on public comments and data pertaining to it, we published a proposed rule (41 FR 24523) to determine approximately 1,700 vascular plants as endangered pursuant to section 4 of the Act. The 1,700 plants included all eleven vernal pool plants considered here.
We published a final rule to list Solano grass (along with four other plants) as endangered on September 28, 1978 (43 FR 44810). A recovery plan for Solano grass and the delta green ground beetle (
Elaphrus viridis
) was subsequently approved on September 11, 1985 (Service 1985c). We failed to complete final listing rules for the other ten vernal pool plants within three years of the proposed listing, however, despite amendments to the Act in 1978 requiring us to withdraw proposed rules which were more than two years old (with a one-year grace period). Accordingly, on December 10, 1979, we withdrew the proposal to list the ten remaining vernal pool plants (44 FR 70796).
We established the remaining vernal pool plants as category 1 candidate species in a Notice of Review (NOR) for plants published December 15, 1980 (45 FR 82480). Category 1 candidates were those species for which data in our possession was sufficient to support proposals to list. In a subsequent NOR published November 28, 1983 (48 FR 53640), we downgraded the status of Contra Costa goldfields, slender Orcutt grass and Colusa grass to category 2. Category 2 candidates were defined as species for which data in our possession indicated listing was possibly appropriate, but for which we lacked substantial data on biological vulnerability and threats to support listing proposals. Another NOR on September 27, 1985, left the status of the remaining vernal pool plants unchanged (50 FR 39526).
On February 2, 1988, we received a petition from the California Native Plant Society (CNPS) to emergency list Butte County meadowfoam as endangered. We published a 90-day administrative finding that the requested action might be warranted on December 30, 1988 (53 FR 53030). On February 15, 1991, we published a proposal to list Butte County meadowfoam as an endangered species (56 FR 6345), and on June 8, 1992, we published a final determination that Butte County meadowfoam was endangered (57 FR 24192).
On February 22, 1990, we published a new NOR which re-established Colusa grass and Contra Costa goldfields as category 1 candidate species (55 FR 6184). In 1991 and 1992, we received additional information regarding threats to succulent owl's-clover, and so returned this species to category 1 status on August 5, 1993 (58 FR 41700), in the same notice proposing to list succulent owl's clover and seven other vernal pool plants under the Act.
On August 5, 1993, we published a proposal to list San Joaquin Valley Orcutt grass, hairy Orcutt grass, Sacramento Orcutt grass, and Greene's tuctoria as endangered; and to list succulent owl's-clover, Hoover's spurge, Colusa grass, and slender Orcutt grass as threatened was published on August 5, 1993 (58 FR 41700). This proposal was primarily based on information supplied by reports to the CNDDB, the Status Survey of the Grass Tribe Orcuttieae and Hoover's Spurge in the Central Valley of California (Stone
et al.
1988), and observations by numerous botanists. Prior to publishing the final rule on these eight plants, we published another NOR on September 30, 1993 (58 FR 51144), indicating that the current status of the vernal pool plants as category 1 candidates remained unchanged. We subsequently published a proposal to list Contra Costa goldfields as endangered on December 19, 1994 (59 FR 65311). Then on March 26, 1997, we published the final rule (62 FR 14338) for the eight plants proposed for listing in 1993. The final rule listed San Joaquin Valley Orcutt grass as threatened, rather than endangered as had originally been proposed, because we determined the threats to its existence to be smaller and less immediate than had previously been thought. All seven other plants were listed as proposed, resulting in a listing of hairy Orcutt grass, Sacramento Orcutt grass and Greene's tuctoria as endangered; and San Joaquin Valley Orcutt grass, succulent owl's clover, Hoover's spurge, Colusa grass and slender Orcutt grass as threatened. Later that same year (June 18, 1997) we published the final rule to list Contra Costa goldfields, the last of the vernal pool plants considered here, as endangered (62 FR 34029).
We did not identify critical habitat in the final listing rules for any of the vernal pool plants or crustaceans considered here because we determined that the threats of increased vandalism and collection of listed species in the areas thus identified would make it imprudent to do so. Based on the interpretation of section 4 of the Act in a number of judicial decisions issued after the not prudent findings for these species were made, however, we have reconsidered those determinations and now consider the designation of critical habitat for the fifteen vernal pool species to be prudent. We are therefore proposing to designate critical habitat here, for the four vernal pool
crustaceans and eleven vernal pool plants covered by the July 23, 2001, court approved settlement agreement in that case.
On August 14, 2002, we filed a motion in
Butte Environmental Council
seeking to modify the deadline of August 15, 2002, for issuance of final critical habitat determinations. We were unable to meet that deadline, and have asked the court to approve a new deadline of September 30, 2003.
Critical Habitat
Critical habitat is defined in section 3(5)(A) of the Act as: (i) The specific areas within the geographic area occupied by a species at the time it is listed in accordance with the Act, on which are found those physical or biological features (I) essential to the conservation of the species and (II) that may require special management considerations or protection; and (ii) specific areas outside the geographic area occupied by a species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. “Conservation” means the use of all methods and procedures that are necessary to bring an endangered or threatened species to the point at which listing under the Act is no longer necessary.
Critical habitat receives protection under section 7 of the Act through the prohibition against destruction or adverse modification of critical habitat with regard to actions carried out, funded, permitted, or authorized by a Federal agency. Section 7 also requires conferences on Federal actions that are likely to result in the destruction or adverse modification of proposed critical habitat. Aside from the added protection that may be provided under section 7, the Act does not provide other forms of protection to lands designated as critical habitat. Because consultation under section 7 of the Act does not apply to activities on private or other non-Federal lands that do not involve a Federal nexus, critical habitat designation would not afford any additional regulatory protections under the Act.
Critical habitat also provides non-regulatory benefits to the species by informing the public and private sectors of areas that are important for species recovery and where conservation actions would be most effective. Designation of critical habitat can help focus conservation activities for a listed species by identifying areas that contain the physical and biological features essential for the conservation of that species, and can alert the public as well as land-managing agencies to the importance of those areas. Critical habitat also identifies areas that may require special management considerations or protection, and may help provide protection to areas where significant threats to the species have been identified, by helping people avoid causing accidental damage to such areas.
In order to be included in a critical habitat designation, the habitat must first be “essential to the conservation of the species.” Critical habitat designations identify, to the extent known and using the best scientific and commercial data available, habitat areas that provide at least one of the physical or biological features essential to the conservation of the species (primary constituent elements, as defined at 50 CFR 424.12(b)). Section 3(5)(C) of the Act states that not all areas that can be occupied by a species should be designated as critical habitat unless the Secretary determines that all such areas are essential to the conservation of the species. Our regulations (50 CFR 424.12(e)) also state that, “The Secretary shall designate as critical habitat areas outside the geographic area presently occupied by the species only when a designation limited to its present range would be inadequate to ensure the conservation of the species.”
Section 4(b)(2) of the Act requires that we take into consideration the economic impact, and any other relevant impact, of specifying any particular area as critical habitat. We may exclude areas from critical habitat designation when the benefits of exclusion outweigh the benefits of including the areas within critical habitat, provided the exclusion will not result in extinction of the species.
Our Policy on Information Standards Under the Endangered Species Act, published on July 1, 1994 (59 FR 34271), provides criteria, establishes procedures, and provides guidance to ensure that our decisions represent the best scientific and commercial data available. It requires that our biologists, to the extent consistent with the Act and with the use of the best scientific and commercial data available, use primary and original sources of information as the basis for recommendations to designate critical habitat. When determining which areas are critical habitat, a primary source of information should be the listing rule for the species. Additional information may be obtained from a recovery plan, articles in peer-reviewed journals, conservation plans developed by States and surveys and studies, and biological assessments or other unpublished materials.
Section 4 of the Act requires that we designate critical habitat based on what we know at the time of designation. Habitat is often dynamic, and species may move from one area to another over time. Furthermore, we recognize that designation of critical habitat may not include all of the habitat areas that may eventually be determined to be necessary for the recovery of the species. For these reasons, critical habitat designations do not signal that habitat outside the designation is unimportant or may not be required for recovery. Areas outside the critical habitat designation will continue to be subject to conservation actions that may be implemented under section 7(a)(1) of the Act and to the regulatory protections afforded by the section 7(a)(2) jeopardy standard and the section 9 prohibitions, as determined on the basis of the best available information at the time of the action. Federally funded or assisted projects affecting listed species outside their designated critical habitat areas may still result in jeopardy findings. Similarly, critical habitat designations made on the basis of the best available information at the time of designation will not control the direction and substance of future recovery plans, HCPs, or other species conservation planning efforts if new information available to these planning efforts calls for a different outcome.
The action of designating critical habitat does not automatically lead to recovery of a listed species, but it may contribute to species recovery. Critical habitat units are not target preserve areas: designation does not target and establish specific preserves and their boundaries. Critical habitat is designated to make Federal agencies aware that these areas are critical to the species. Although the designation of critical habitat can identify areas where a variety of conservation strategies may be developed to ensure the survival and recovery of target species, the development of these strategies are most appropriately taken through local planning efforts, such as the development of HCPs. The action of designating critical habitat does not result in the creation of management plans, establish numerical population goals, and/or prescribe specific management actions, whether inside or outside of such designated critical habitat. Specific management recommendations for areas designated as critical habitat are most appropriately addressed in recovery, conservation, and management plans, and through consultations and permits under section 7 and section 10 of the Act.
Prudency Redetermination
Section 4(a)(3) of the Act, as amended, and implementing regulations (50 CFR 424.12) require that, to the maximum extent prudent and determinable, we designate critical habitat at the time the species is determined to be endangered or threatened. At the time of the final listing determination (62 FR 34029, 62 FR 14338, 59 FR 48136, 57 FR 24192), we found that designation of critical habitat was not prudent for the vernal pool crustaceans and plants (excluding Solano grass). At the time of final listing of Solano grass (43 FR 44810), we did not make any determination about whether or not designation of critical habitat was prudent. Our regulations (50 CFR 424.12(a)(1)) state that designation of critical habitat is not prudent when one or both of the following situations exist—(1) The species is threatened by taking or other human activity, and identification of critical habitat can be expected to increase the degree of such threat to the species, or (2) such designation of critical habitat would not be beneficial to the species. In our final listing rules for the vernal pool crustaceans and plants (excluding Solano grass), we believed that publication of precise maps and descriptions of critical habitat for the vernal pool crustaceans and plants could make these species more vulnerable to incidents of vandalism or other human activities such as discing, grading, or filling (62 FR 34029, 62 FR 14338, 59 FR 48136, 57 FR 24192). In addition, we determined that publication of precise maps and descriptions of critical habitat for the vernal pool plants would increase the vulnerability of these species to incidents of collection (62 FR 34029, 62 FR 14338, 57 FR 24192). Therefore, we determined that the designation of critical habitat would increase the degree of threat to the vernal pool crustaceans and plants. We also determined that designation of critical habitat was not beneficial for the vernal pool plant species (excluding Solano grass) because many populations of these species were found on private lands (62 FR 34029, 62 FR 14338, 57 FR 24192). For Butte County meadowfoam and Contra Costa goldfields, we believed that Federal involvement in the areas where these plant species occurred could be identified without designation of critical habitat (62 FR 34029, 57 FR 24192). For eight of the vernal pool plant species (succulent owl's-clover, Hoover's spurge, Colusa grass, San Joaquin Valley Orcutt grass, hairy Orcutt grass, slender Orcutt grass, Sacramento Orcutt grass, and Greene's tuctoria), we believed that Federal agencies were aware of the species' presence and were already addressing conservation efforts where the species were found on Federal lands (62 FR 14338).
In 1995, the CDFG received a grant from the U.S. Environmental Protection Agency (EPA) to map vernal pools in particular areas for conservation purposes (Vendlinski 2000). As a result of this effort, the CDFG published a report which delineated 17 vernal pool regions throughout California (Keeler-Wolf
et al.
1998). In 1997, Robert Holland's original 1973-1974 map of vernal pools in the Central Valley was updated and the results were documented Holland (1998). In 1998, we published the Recovery Plan for Vernal Pools of Southern California (Service 1998) which outlined recovery strategies for seven vernal pool species (two vernal pool crustaceans and five vernal pool plants) including the San Diego fairy shrimp (
Branchinecta sandiegonensis
). The release of these data resulted in the widespread distribution of information about vernal pool habitat and its location to the public and to local jurisdictions for planning purposes. Since the release of these data, we have not documented an increase in the threats to the species addressed in this rule through vandalism, collection, habitat destruction, or other means. In contrast, we have witnessed an increase in public interest in the species and their conservation through survey efforts by species experts, scientific research, regional and local planning, and educational outreach. Since listing of the vernal pool crustaceans and plants, several vernal pool conservation planning efforts have been initiated by public agencies and non-government organizations. For example, in 1997 the Framework Agreement for the Interagency Vernal Pool Stewardship Initiative was signed by a number of Federal and State agencies; this agreement encourages coordination of vernal pool conservation efforts on a regional scale between the signatory agencies.
Based on the lack of an increase in vandalism threats, we have reconsidered our evaluation of our original prudency determination. We have determined that the threats to the vernal pool crustaceans and plants and their habitat from the specific instances of habitat destruction we identified in the final listing rules do not outweigh the broader educational, regulatory, and other possible benefits that a designation of critical habitat would provide for these species. The instances of likely vandalism, though real, have been relatively isolated. Consequently, we conclude that designating critical habitat will not increase incidences of habitat vandalism above current levels for these species. In the absence of finding that critical habitat would increase threats to a species, if there are any benefits to critical habitat designation, then a prudent finding is warranted. The potential benefits include: (1) Triggering consultations under section 7 of the Act in new areas where it would not otherwise occur because, for example, it is or has become unoccupied or the occupancy is in question; (2) focusing conservation activities on the most essential areas; (3) providing educational benefits to State or county governments or private entities; and, (4) preventing people from causing inadvertent harm to the species. Therefore, we conclude that the benefits of designating critical habitat on lands essential for the conservation of the vernal pool crustaceans and plants outweigh the risks of increased vandalism resulting from such designation. Critical habitat for the 4 vernal pool crustaceans and 11 vernal pool plants addressed herein is prudent and we are subsequently proposing critical habitat for them in this proposed rule.
All of the proposed critical habitat units contain one or more of the primary constituent elements for the vernal pool crustaceans or plants addressed in this proposed rule. However, as stated earlier, vernal pool crustaceans and plants occur in ephemeral pools that may not be present throughout a given year or from year to year.
In summary, in determining areas that are essential to conserve the species addressed in this proposed rule, we used the best scientific information available to us. The critical habitat areas described below constitute our best assessment of areas needed for the species' conservation.
Methods
In determining critical habitat for vernal pool crustaceans and vernal pool plants we used the best scientific and commercial data available. This included data and information contained in the final rules listing the 15 species addressed herein, research and survey observations published in peer reviewed articles, the Vernal Pools of Southern California Final Recovery Plan (Service 1998), data collected for the development of HCPs, reports submitted by biologists holding section 10(a)(1)(A) recovery permits, data collected for the development of a
Wetland Conservation Plan in Oregon, reports and documents that are on file in the Service's field offices, and personal discussions with experts outside of the Service with extensive knowledge of vernal pool species and habitats.
We utilized Geographic Information System (GIS) data derived from a variety of Federal, State, and local agencies, and from private organizations and individuals. To identify where vernal pool species and habitats occur we evaluated GIS data of vernal pool habitats by Holland (1998 and 2002), and species occurrences information from the CNDDB (2001). We presumed occurrences identified in CNDDB to be extant until we received documentation that the occurrences have been extirpated. We also relied on unpublished species occurrence data contained within our files. We produced preliminary maps using GIS information that plotted species occurrences and vernal pool habitats superimposed on SPOT imagery (CNES/SPOT Image Corporation 1993-2000). The use of SPOT imagery allowed us to identify landmarks such as roads, cities, rivers, and urban areas.
Because the minimum mapping unit of the Holland (1998 and 2002) vernal pool habitat data was 16 ha (40 ac) and the resolution of the SPOT imagery did not allow us to identify all vernal pool habitat areas, we then refined unit boundaries based on additional GIS data layers when necessary and available, including soils information from the Soil Survey Geographic (SSURGO) data bases (U.S. Department of Agriculture (USDA) 1998-2001), and the California State Soil Geographic (STATSGO) data bases (USDA 1994). We used geologic information developed by the California Department of Mines and Geology (CDMG) (2000) and Liss (2001). To identify the extent of flat or gently sloping topography where vernal pools are found we evaluated Digital Elevation Models from the U.S. Geologic Survey (2000).
We also used a number of local GIS data sets for specific areas, including information developed through the Riverside Multiple Species HCP and the Vernal Pools of Southern California Final Recovery Plan (Service 1998), habitat mapping for Butte County (EPA 1994), Tehama County (2001), Shasta County (2001) Placer County (Glazner 2001), Solano County (2000), Yolo County (1995), Sacramento County (1999) and San Joaquin County (2000) in California, and by the Rogue Valley Council of Governments in Oregon (Evans 2000). Other smaller scale mapping efforts were reviewed from Solano County Farmlands and Open Space (2000) and East Bay Regional Parks District (2001). The specific layers used and the methodology employed for each unit is described within the unit descriptions. To determine land ownership within each unit we used data from the State of California (Davis
et al.
1998) and the U.S. Bureau of Indian Affairs in Sacramento, California (2001).
Primary Constituent Elements
In accordance with section 3(5)(A)(i) of the Act and regulations at 50 CFR 424.12, in determining which areas to propose as critical habitat, we consider those physical and biological features (primary constituent elements) that are essential to the conservation of the species and that may require special management considerations or protection. These features include, but are not limited to—space for individual and population growth, and for normal behavior; food, water, air, light, minerals, or other nutritional or physiological requirements; cover or shelter; sites for breeding, reproduction, and dispersal; and habitats that are protected from disturbance or are representative of the historic geographical and ecological distributions of a species.
When considering the designation of critical habitat for vernal pool crustaceans, we focused on the principal biological and physical features that support vernal pool crustacean feeding, growth, breeding, reproduction, and dispersal. Vernal pool crustaceans are found only in ephemeral wetland habitats that contain water during the winter, when temperatures are suitable for cyst hatching and juvenile development. Individuals have never been found in riverine, marine, or other permanent bodies of water.
Generally, we identified two primary constituent elements for all four vernal pool crustacean species addressed in this proposed rule. Each species has primary constituent elements that differ slightly from these general elements discussed in later sections of this rule. We determined that these proposed primary constituent elements of critical habitat provide for the physiological, behavioral, and ecological requirements of the vernal pool crustaceans.
The first primary constituent element provides the aquatic environment required for cyst incubation and hatching, growth and maturation, reproduction, feeding, sheltering, and dispersal, and the appropriate periods of dessication for cyst dormancy and to eliminate predators such as bullfrogs, fish, and other aquatic predators that depend on year round inundation of wetland habitats to survive. We conclude this element is essential to the conservation of vernal pool crustaceans because these species are ecologically dependent on seasonal fluctuations, such as absence or presence of water during specific times of the year, and duration of inundation (59 FR 48136). They cannot persist in perennial wetlands or wetlands that are inundated for the majority of the year, nor can they persist without periodic seasonal inundation.
The second primary constituent element is essential to maintain the aquatic phase of the vernal pool habitat. The entire vernal pool complex, including the pools, swales, and associated uplands, is essential to support the aquatic functions of the vernal pool habitat. Although the uplands are not actually occupied by vernal pool crustaceans, they nevertheless are essential to the conservation of vernal pool habitat and crustaceans because they maintain the aquatic phase of vernal pools and swales. Associated uplands are also essential to provide nutrients that form the basis of the vernal pool food chain, including a primary food source for the vernal pool crustaceans.
We have used vernal pool complexes as the basis for determining populations of vernal pool crustaceans since the species were first proposed for listing. The final rule to list the four vernal pool crustaceans states that “[t]he genetic characteristics of the three fairy shrimp and vernal pool tadpole shrimp, as well as ecological conditions, such as watershed contiguity, indicate that populations of these animals are defined by pool complexes rather than by individual vernal pools' (Fugate 1992, Fugate 1998, King 1996). Therefore, the most accurate indication of the distribution and abundance of the four vernal pool crustaceans is the number of inhabited vernal pool complexes. Individual vernal pools occupied by the four species listed herein are most appropriately referred to as “subpopulations” (59 FR 48137). Our use of vernal pool complexes to define populations of the four listed crustaceans was upheld by the U.S. District Court in post-listing challenge to the listing (
Building Industry Association of Superior California
). The July 25, 1997, decision stated: “The Court finds that the plaintiffs were on notice that the FWS would consider vernal pool complexes as a basis for determining fairy shrimp populations. The Court also concludes that the use of this methodology was neither arbitrary nor capricious.” The Court of Appeals
for the D.C. Circuit upheld the district court's decision, and the Supreme Court has declined to hear the case.
In identifying specific primary constituent elements for each of the four vernal pool crustaceans, we expanded upon the general primary constituent elements described above and focused on the specific habitat requirements of each individual vernal pool crustacean species. These habitat requirements and the specific primary constituent elements for each vernal pool crustacean are described below.
Conservancy Fairy Shrimp Primary Constituent Elements
The Conservancy fairy shrimp is uniquely adapted to the ephemeral conditions of its vernal pool habitat. Helm (1998) found that the life span and maturation rate of Conservancy fairy shrimp did not differ significantly from other fairy shrimp species under the conditions he observed. Helm (1998) found that Conservancy fairy shrimp reached maturity in an average of 46 days, and lived for as long as 154 days. However, aquatic invertebrate growth rates are largely controlled by water temperature and can vary greatly (Eriksen and Brown 1980, Helm 1998). Eriksen and Belk (1999) observe that Conservancy fairy shrimp produce large cohorts of offspring, and is an “especially hyperactive swimmer and filter feeder.” Conservancy fairy shrimp have only been observed to produce one cohort of offspring each wet season (Eriksen and Belk 1999).
Observations suggest this species is generally found in pools that are relatively large and turbid (King
et al.
1996, Helm 1998, Eriksen and Belk 1999). Helm (1998) found that most Conservancy fairy shrimp occurrences were generally within vernal pools formed on fertile, basin rim soils. These pool types may be over several acres in size, and are often alkaline. Soil types where the species is known to occur include Anita, Pescadero, Riz, Solano, Edminster, San Joaquin, and Peters soil series.
Conservancy fairy shrimp occur with several other vernal pool crustaceans, including vernal pool fairy shrimp, California linderiella, and vernal pool tadpole shrimp (King
et al.
1996, Eriksen and Belk 1999, Helm 1998). In general, Conservancy fairy shrimp have very large populations within a given pool, and is usually the most abundant fairy shrimp when more than one fairy shrimp species is present (Helm 1998, Eriksen and Belk 1999). Conservancy fairy shrimp are eaten by vernal pool tadpole shrimp (Alexander and Schlising 1997), as well as a variety of insect and vertebrate predator species.
When considering the designation of critical habitat for Conservancy fairy shrimp, we focused on the principal biological and physical features that support Conservancy fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions, and their associated uplands. The primary constituent elements for Conservancy fairy shrimp include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for Conservancy fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to large, playa vernal pools often on basin rim landforms and alkaline soils, but which are dry during the summer and do not necessarily fill with water every year; and
(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Conservancy fairy shrimp. We determined the primary constituent elements of critical habitat for Conservancy fairy shrimp based on studies on their habitat and population biology including but not limited to—Eng
et al.
1990, Gallagher 1996, Alexander and Schlising 1997, Helm 1998, Eriksen and Belk 1999.
Longhorn Fairy Shrimp Primary Constituent Elements
Longhorn fairy shrimp are known only from three general locations, and each of these sites contain very different types of vernal pool habitats. Longhorn fairy shrimp in Contra Costa and Alameda counties live in small, clear, sandstone outcrop pools. These sandstone pools have a pH near neutral, and very low alkalinity and conductivity (Eriksen and Belk 1999). Water temperatures in these pools have been measured between 10 and 18°C (50 and 64°F). In the other two locations in Merced and San Luis Obispo counties where longhorn fairy shrimp occur, they are found in turbid, alkaline, grassland vernal pools (Helm 1998, Eriksen and Belk 1999). Water temperatures in these grassland vernal pools tend to be warmer, between 10 and 28°C (50.0 to 82.0°F). However, no experimental studies have been conducted to determine the specific habitat requirements of longhorn fairy shrimp, and until research addressing the tolerance of longhorn fairy shrimp to a range of temperatures and water chemistries, its potential to occur in other types of vernal pool habitats cannot be ruled out.
Like other fairy shrimp, longhorn fairy shrimp are highly adapted to the variable conditions of vernal pool habitats. Longhorn fairy shrimp require a minimum of 23 days, but averaged 43 days, to reach maturity in artificial pools described by Helm (1998). However, Helm (1998) found no significant differences between the life span or reproductive rate of longhorn fairy shrimp and other species of fairy shrimp he studied.
When considering the designation of critical habitat for longhorn fairy shrimp, we focused on the principal biological and physical features that support longhorn fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for the longhorn fairy shrimp include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for longhorn fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to sandstone outcrop pools and turbid alkaline pools, but which are dry during the summer and do not necessarily fill with water every year; and
(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically
functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for longhorn fairy shrimp. We determined the primary constituent elements of critical habitat for longhorn fairy shrimp based on studies on their habitat and population biology including but not limited to— Eng
et al.
1990, Fugate 1992, Gallagher 1996, Fugate 1998, Helm 1998, and Eriksen and Belk 1999.
Vernal Pool Fairy Shrimp Primary Constituent Elements
Vernal pool fairy shrimp generally will not hatch until water temperatures drop to below 10°C (50°F) (Gallagher 1996, Helm 1998). Vernal pool fairy shrimp are capable of hatching multiple times within a single wet season if conditions are appropriate. Helm (1998) observed 6 separate hatches of vernal pool fairy shrimp within a single wet season, and Gallagher (1996) observed 3 separate hatches of vernal pool fairy shrimp in vernal pools in Butte County.
Vernal pool fairy shrimp have been documented to live for as long as 147 days Helm (1998), but their life cycle and longevity is dependant upon water temperature as well as other environmental factors. Vernal pool fairy shrimp can reproduce in as few as 18 days at optimal conditions of 20°C (68°F) and can complete their life cycle in as little as 63 days (Gallagher 1996, Helm 1998). However, maturation and reproduction rates of vernal pool crustaceans are controlled by water temperature and can vary greatly (Eriksen and Brown 1980, Helm 1998). Helm (1998) observed that vernal pool fairy shrimp did not reach maturity until 41 days at water temperatures of 15°C (59°F). Vernal pool fairy shrimp have been collected at water temperatures as low as 4.5°C (40°F) (Eriksen and Belk 1999), however, the species has not been found in water temperatures above about 23°C (73°F) (Helm 1998, Eriksen and Belk 1999).
Vernal pool fairy shrimp occupy a variety of different vernal pool habitats, from small, clear, sandstone rock pools to large, turbid, alkaline, grassland valley floor pools (Eng
et al.
1990, Helm 1998, CNDDB 2001). The pool types where the species has been found include Northern Hardpan, Northern Claypan, Northern Volcanic Mud Flow, and Northern Basalt Flow vernal pools which formed on a variety of geologic formations and soil types (CNDDB 2001). Although vernal pool fairy shrimp have been collected from large vernal pools, including one exceeding 10 ha (25 ac) in area (Eriksen and Belk 1999), they are most frequently found in pools measuring less than 0.02 ha (0.05 ac) in area (Helm 1998, Gallagher 1996). The species occurs at elevations from 10 m (33 ft) to 1,220 m (4,003 ft) (Eng
et al.
1990), and is typically found in pools with low to moderate amounts of salinity or total dissolved solids (Keeley 1984, Syrdahl 1993). Vernal pools are mostly rain fed, resulting in low nutrient levels and dramatic daily fluctuations in pH, dissolved oxygen, and carbon dioxide (Keeley and Zedler 1998). Although there are many observations of the environmental conditions where vernal pool fairy shrimp have been found, there have been no experimental studies investigating the specific habitat requirements of this species.
When considering the designation of critical habitat for vernal pool fairy shrimp, we focused on the principal biological and physical features that support vernal pool fairy shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for vernal pool fairy shrimp include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool fairy shrimp incubation, reproduction, dispersal, feeding, and sheltering, including but not limited to Northern Hardpan, Northern Claypan, Northern Volcanic Mud Flow, and Northern Basalt Flow vernal pools formed on a variety of geologic formations and soil types, but which are dry during the summer and do not necessarily fill with water every year; and
(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for one of these species. We determined the primary constituent elements of critical habitat for vernal pool fairy shrimp based on studies on their habitat and population biology including but not limited to—Eng
et al.
1990, Fugate 1992, Gallagher 1996, Fugate 1998, Helm 1998, and Eriksen and Belk 1999.
Vernal Pool Tadpole Shrimp Primary Constituent Elements
Although the vernal pool tadpole shrimp is adapted to survive in ephemeral vernal pool habitat, the species has a relatively long life span compared to other vernal pool crustaceans. Helm (1998) found that vernal pool tadpole shrimp lived significantly longer than any other species observed under the same conditions except California linderiella (
Linderiella occidentalis
). Vernal pool tadpole shrimp continue growing throughout their lives, periodically molting their shells. These shells can often be found in vernal pools where the species occurs. Helm (1998) found that vernal pool tadpole shrimp took a minimum of 25 days to mature and the mean age at first reproduction was 54 days. Other researchers have observed that vernal pool tadpole shrimp generally take between 21 to 28 days to mature (Ahl 1991, King 1996). Ahl (1991) found that reproduction did not begin until individuals were larger than 10 mm (0.39 in) carapace length. Variation in growth and maturation rates may be a result of differences in water temperature, which strongly influences the growth rates of aquatic invertebrates.
Vernal pool tadpole shrimp occur in a wide variety of vernal pool habitats (Helm 1998). They have been found in pools with water temperatures ranging from 10°C (50°F) to 29°C (84°F) and pH ranging from 6.2 to 8.5 (Syrdahl 1993, King 1996). However, vernal pools exhibit daily and seasonal fluctuations in pH, temperature, dissolved oxygen, and other water chemistry characteristics (Syrdahl 1993, Scholnick 1995, Keeley 1998a). Determining vernal pool tadpole shrimp habitat requirements is not possible based on anecdotal evidence, and the tolerances of this species to specific environmental conditions have yet to be determined. Although vernal pool tadpole shrimp are found on a variety of geologic
formations and soil types, Helm (1998) found that over 50 percent of vernal pool tadpole shrimp occurrences were on high terrace landforms and Redding and Corning soils. Platenkamp (1998) found that vernal pool tadpole shrimp presence differed significantly between geomorphic surfaces at Beale Air Force Base and the species was most likely to be found on Riverbank formation.
When considering the designation of critical habitat for vernal pool tadpole shrimp, we focused on the principal biological and physical features that support vernal pool tadpole shrimp feeding and growth, breeding and reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for vernal pool fairy shrimp include:
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths that typically become inundated during winter rains and hold water for sufficient lengths of time necessary for vernal pool tadpole shrimp incubation, reproduction, dispersal, feeding, and sheltering, but which are dry during the summer and do not necessarily fill with water every year; including but not limited to vernal pools on Redding and Corning soils on high terrace landforms, and
(2) The geographic, topographic, and edaphic features that support aggregations or systems of hydrologically interconnected pools, swales, and other ephemeral wetlands and depressions within a matrix of surrounding uplands that together form hydrologically and ecologically functional units called vernal pool complexes. These features contribute to the filling and drying of the vernal pool, and maintain suitable periods of pool inundation, water quality, and soil moisture for vernal pool crustacean hatching, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for vernal pool tadpole shrimp. We determined the primary constituent elements of critical habitat for vernal pool tadpole shrimp based on studies on their habitat and population biology including but not limited to—Longhurst 1955, Lynch 1966, Ahl 1991, King 1996, and Helm 1998.
General Primary Constituent Elements for Vernal Pool Plants
The primary constituent elements of critical habitat for vernal pool plants are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. All of the vernal pool plants addressed in this proposed rule are found only in ephemeral wetlands including vernal pools and swales. None of these species are known to occur in permanent wetlands, and none are found in strictly upland areas that are never inundated.
Generally, we identified two primary constituent elements for all eleven vernal pool plants addressed in this proposed rule. Each species has primary constituent elements that differ slightly from these general elements discussed in later sections of this rule. We determined that these proposed primary constituent elements of critical habitat provide for the physiological and ecological requirements of the vernal pool plants.
The first primary constituent element provides the necessary soil moisture and aquatic environment required for seed germination, growth and maturation, reproduction, and dispersal, and the appropriate periods of dry-down for seed dormancy. Both the wet and dry phases of the vernal pool help to reduce competition with strictly terrestrial or strictly aquatic plant species. The wet phase provides the necessary cues for germination and growth, while the drying phase allows the vernal pool plants to flower and produce seeds. We conclude this element is essential to the conservation of the vernal pool plants because these species are ecologically dependent on seasonal fluctuations, such as absence or presence of water during specific times of the year, and duration of inundation and the rate of drying of their habitats. They cannot persist in perennial wetlands or wetlands that are inundated for the majority of the year, nor can they persist without periodic seasonal inundation.
The second primary constituent element is essential to maintain both the aquatic phase and the drying phase of the vernal pool habitat. Although the vernal pool plants addressed in this proposed rule do not occur in the strictly upland areas surrounding vernal pools, they are dependent on these upland areas to maintain the aquatic and drying phases of the vernal pool. The germination of vernal pool plants is dependant on the timing and length of inundation of the vernal pool. The rate of vernal pool drying, during which vernal pool plants must flower and produce seeds, is also largely controlled by interactions between the vernal pool and the surrounding uplands (Hanes
et al.
1990, Hanes and Stromberg 1998).
In identifying specific primary constituent elements for each of the eleven vernal pool plant species addressed in this proposed rule, we expanded upon the general primary constituent elements described above to focus on the specific habitat requirements of each of the eleven individual species. These habitat requirements and the specific primary constituent elements for each species are described below.
Butte County Meadowfoam Primary Constituent Elements
The swales and vernal pools where Butte County meadowfoam grows are on intermediate fan terraces (Kelley and Associates Environmental Sciences 1992) in annual grasslands with a mima mound topography. Large cobbles are present throughout the pools and swales (Jokerst 1989). These pools are associated with Tuscan, Redbluff, Riverbank, and Modesto geologic formations, and most of them occur on soils of the Tuscan-Anita and the Redding-Igo complexes. Anita and Igo soils are confined to the pools and swales. Tuscan and Redding soils are restricted to the mounds. Anita soils can be up to 50 cm (19.7 in) deep, whereas Igo soils are no more than 18 cm (7.1 in) deep; the two soils are underlain by iron-silica cemented and indurated hardpan, respectively (Kelley and Associates Environmental Sciences 1993). Butte County meadowfoam has been observed on Anita clay soils annually regardless of rainfall but appears on Igo soils only in years of above average rainfall (Kelley and Associates Environmental Sciences 1992a, Crompton 1993, Schonholtz
in litt.
1995), presumably because the former can hold approximately twice as much moisture (Kelley and Associates Environmental Sciences 1993). Confirmed occurrences have been found at 50 to 90 m (165 to 300 ft) in elevation (McNeill and Brown 1979, CNDDB 2001).
The primary constituent elements of critical habitat for Butte County meadowfoam are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent
elements for Butte County meadowfoam include:
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Butte County meadowfoam germination, growth and reproduction, including but not limited to vernal pool swales and the margins of vernal pools on the Tuscan, Redbluff, Riverbank, and Modesto geologic formations underlain by Tuscan-Anita and Igo-Redding complex soils among others. These habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and
(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Butte County meadowfoam germination, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Butte County meadowfoam. We determined the primary constituent elements of critical habitat for Butte County meadowfoam based on studies of their habitat and population biology including but not limited to—Kalin-Arroyo 1973, Dole 1988, Jokerst 1989, Kelley and Associates Environmental Sciences 1992a, and Crompton 1993.
Contra Costa Goldfields Primary Constituent Elements
Contra Costa goldfields typically grows in vernal pools, swales, moist flats, and depressions within a grassland matrix (CNDDB 2001). However, several historical collections were from populations growing in the saline-alkaline transition zone between vernal pools and tidal marshes on the eastern margin of the San Francisco Bay (Baye USFWS
in litt.
2000a). The herbarium sheet for one of the San Francisco Bay specimens notes that the species also grew in evaporating ponds used to concentrate salt (Baye
in litt.
2000b). The vernal pool types from which this species has been reported are Northern Basalt Flow, Northern Claypan, and Northern Volcanic Ashflow (Sawyer and Keeler-Wolf 1995). The landforms and geologic formations for sites where Contra Costa goldfields occurs have not yet been determined. Most occurrences of Contra Costa goldfields are at elevations of 2 to 61 m (6 to 200 ft), but the recently discovered Monterey County occurrences are at 122 m (400 ft) and one Napa County occurrence is at 445 m (1,460 ft) elevation (CNDDB 2001).
The soil types that maintain these vernal pool habitats for Contra Costa goldfields have not yet been identified for most localities. The soil series from which it is known are Aiken, Antioch, Concepcion, Conejo, Crispin, Haire, Linne, Los Robles, Rincon, Solano, and San Ysidro, plus the Arnold-Santa Ynez, Hambright-rock outcrop, and Los Osos complexes. Soil textures, where known, are clays or loams. At least in Solano County and on the shores of San Francisco Bay, Contra Costa goldfields grows in alkaline or saline-alkaline sites (Baye
in litt.
2000a, Baye
in litt.
2000b, CNDDB 2001).
The primary constituent elements of critical habitat for Contra Costa goldfields are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Contra Costa goldfields include—
(1) Vernal pools, swales, moist flats, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Contra Costa goldfields germination, growth and reproduction, including, but not limited to, vernal pools on clay soils from a variety of soils series, rock outcrop pools on basalt flows, and vernal pools in saline alkaline transition zones with tidal marsh habitats. All of these habitats typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and
(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Contra Costa goldfields germination, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Contra Costa goldfields. We determined the primary constituent elements of critical habitat for Contra Costa goldfields based on studies on their habitat and population biology including but not limited to—Ornduff 1966, Ornduff 1979, Crawford and Ornduff 1989, Skinner and Pavlik 1994.
Hoover's Spurge Primary Constituent Elements
Vernal pools from which Hoover's spurge has been reported are classified as Northern Hardpan and Northern Claypan vernal pools (Sawyer and Keeler-Wolf 1995). The pools supporting this species vary in size from 0.19 to 243 ha (0.47 to 600 ac), with a median area of 0.58 ha (1.43 ac) (Stone
et al.
1988). Many occurrences consist of multiple pools that vary in area and in depth, yet not all pools at a site support Hoover's spurge. Deeper pools apparently provide better habitat for this species because the duration of inundation is longer. This species may occur along the margins or in the deepest portions of the dried pool bed (Stone
et al.
1988, Alexander and Schlising 1997). A particularly important feature of Hoover's spurge microhabitat, at least in the deeper pools, is that it is nearly devoid of other vegetation, and thus competition from other plants is reduced (Stone
et al.
1988).
Vernal pools supporting Hoover's spurge occur mostly on alluvial fans or terraces of ancient rivers or streams, with a few on the rim of the Central Valley basin. Hoover's spurge is found on a wide variety of soils, which range in texture from clay to sandy loam. Soil series from which it has been reported include Anita, Laniger, Lewis, Madera, Meikle, Riz, Tuscan, Whitney, Willows. All of these soils may not be equally suitable for this species, however. For example, in one Vina Plains pool, Hoover's spurge grew primarily in the portion that was underlain by Tuscan loam and was nearly absent from the portion underlain by Anita clay (Alexander and Schlising 1997).
In the Sacramento Valley occupied pools are on acidic soils over iron-silica cemented hardpan. Most pools supporting Hoover's spurge in the San Joaquin Valley are on neutral to saline-alkaline soils over lime-silica cemented hardpan or claypan (Broyles 1987, Stone
et al.
1988, Sawyer and Keeler-Wolf 1995, CNDDB 2001). Occurrences of
Hoover's spurge have been reported from elevations ranging from 26 m (85 ft) in Glenn County to 128 m (420 ft) in Tehama County (CNDDB 2002).
The primary constituent elements of critical habitat for Hoover's spurge are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Hoover's spurge include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Hoover's spurge germination, growth and reproduction, including but not limited to vernal pools formed on neutral to saline-alkaline soils over lime-silica cemented hardpan or claypan, or on acidic soils over iron-silica cemented hardpan, that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and
(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Hoover's spurge germination, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Hoover's spurge. We determined the primary constituent elements of critical habitat for Hoover's spurge based on studies on their habitat and population biology including but not limited to—Broyles 1987, Stone
et al.
1988, and Alexander and Schlising 1997.
Succulent Owl's-Clover Primary Constituent Elements
Succulent owl's-clover is known mostly from vernal pools occurring on alluvial terrace landforms. These pool types have been described as both Northern Claypan and Northern Hardpan vernal pools (Sawyer and Keeler-Wolf 1995) within annual grassland communities (CNDDB 2001). However, it is found on Northern Basalt Flow vernal pools on Hideaway soils series at one location in the San Joaquin Valley. It is known from both small and large pools (EIP Associates 1999). Although not all pools occupied by this taxon have been studied in detail, Stebbins
et al.
(1995) collected data on six occupied pools in Fresno and Madera counties. Some were typical “bowl-like” pools, whereas others were more similar to swales. This subspecies has been reported from pools with both long and short inundation periods (EIP Associates 1999) and from both shallow and “abnormally deep vernal pools,” but approximate depth of these pools was not given (CNDDB 2001).
Soil series supporting succulent owl's-clover include Amador, Anderson, Corning, Fallbrook, Keyes, Pentz, Ramona, Redding, San Joaquin, Vista, and Yokohl, as well as the Pollasky-Montpellier complex. Soil textures at those sites range from extremely stony loam to loamy clay. In the proposed UC Merced campus and community area, the species is found primarily on Redding gravelly loam; however, Corning, Keyes, and Pentz soils also contain occurrences of the species (EIP Associates 1999). Populations of succulent owl's-clover have been reported from elevations of 24 m (80 ft) at the San Joaquin County site to 700 m (2,300 ft) at Kennedy Table in Madera County (CNDDB 2001).
The primary constituent elements of critical habitat for succulent owl's-clover are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for succulent owl's-clover include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain succulent owl's-clover germination, growth and reproduction, including but not limited to hardpan vernal pools on alluvial terraces and San Joaquin, Redding, Corning, Keyes, and Pentz soils series, among others, and northern basalt flow vernal pools on Hideaway soils series, that typically become inundated during winter rains, but are dry during the summer and do not necessarily fill with water every year; and
(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for succulent owl's-clover germination, growth, reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for succulent owl's-clover. We determined the primary constituent elements of critical habitat for succulent owl's-clover based on studies of their habitat and population biology including but not limited to—Hoover 1968, Chuang and Heckard 1991, Chuang and Heckard 1993, and EIP Associates 1999.
Colusa Grass Primary Constituent Elements
Colusa grass has the broadest ecological range among the Orcuttieae. It occurs on the rim of alkaline basins in the Sacramento and San Joaquin valleys, as well as on acidic soils of alluvial fans and stream terraces along the eastern margin of the San Joaquin Valley and into the adjacent foothills (Stone
et al.
1988). Colusa grass has been found in Northern Claypan and Northern Hardpan vernal pool types (Sawyer and Keeler-Wolf 1995) within rolling grasslands (Crampton 1959). This species typically grows in the deepest portion of the pool (Crampton 1959) but also may occur on the margins (Hoover 1937, Stone
et al.
1988). Deeper pools are most likely to provide the long inundation period required for germination (EIP Associates 1999).
Several soil series maintain the vernal pool habitats where Colusa grass is found. Solano and Yolo county sites where Colusa grass grows contain vernal pools formed by soils in the Pescadero series, whereas those in central Merced County are formed by soils in the Landlow and Lewis series (Silveira in litt. 2000). The eastern Merced County and Stanislaus County sites include vernal pool habitats formed by the Bear Creek, Corning, Greenfield, Keyes, Meikle, Pentz, Peters, Raynor, Redding, and Whitney series (Stone
et al.
1988, EIP Associates 1999, CNDDB 2002). The type and composition of impermeable layers underlying occupied vernal pools also vary, ranging from claypan in the Sacramento Valley to lime-silica cemented hardpan in the San Joaquin Valley basins, to iron-silica cemented hardpan in the eastern margin of the San Joaquin Valley. Tuffaceous
alluvium underlies some eastern San Joaquin Valley pools and intermittent streams where Colusa grass grows (Stone
et al.
1988).
The primary constituent elements of critical habitat for Colusa grass are those habitat components that are essential for the primary biological needs of germination, growth, reproduction, and dispersal. These primary constituent elements are found in areas that support vernal pools, swales, or other ephemeral ponds and depressions and their associated uplands. The primary constituent elements for Colusa grass include—
(1) Vernal pools, swales, and other ephemeral wetlands and depressions of appropriate sizes and depths and the adjacent upland margins of these depressions that sustain Colusa grass germination, growth and reproduction, and that typically become inundated during winter rains, including but not limited to vernal pools formed on the rim of alkaline basins in the Sacramento and San Joaquin valleys, as well as on acidic soils of alluvial fans and stream terraces along the eastern margin of the San Joaquin Valley and into the adjacent foothills. All of these pool types are dry during the summer and do not necessarily fill with water every year; and
(2) The associated watershed(s) and hydrologic features, including the pool basin, swales, and surrounding uplands (which may vary in extent depending on pool size and depth, soil type and depth, hardpan or claypan type and extent, topography, and climate) that contribute to the filling and drying of the vernal pool or ephemeral wetland, and that maintain suitable periods of pool inundation, water quality, and soil moisture for Colusa grass germination, growth and reproduction, and dispersal, but not necessarily every year.
All of the above described primary constituent elements do not have to occur simultaneously within a unit for the unit to constitute critical habitat for Colusa grass. We determined the primary constituent elements of critical habitat for Colusa grass based on studies on their habitat and population biology including but not limited to—Crampton 1976, Griggs 1980, Reeder 1982, Griggs and Jain 1983, Keeley 1998a, and Stone
et al.
1988.
Greene's Tuctoria Primary Constituent Elements
Greene's tuctoria has been found in three types of vernal pools: Northern Basalt Flow, Northern Claypan, and Northern Hardpan (Sawyer and Keeler-Wolf 1995, Stone
et al.
1988). Occupied pools are or were underlain by iron-silica cemented hardpan, tuffaceous alluvium, or claypan (Stone
et al.
1988). Of pools where the species was known to be extant in 1987, the median size was 0.6 ha (1.5 ac), with a range of 50 m2 (0.01 ac) to 3.4 ha (8.4 ac) (Stone
et al.
1988). Stone
et al.
(1988) noted that Greene's tuctoria grew in shallower pools than other members of the tribe or on the shallow margins of deeper pools, but they did not quantify p
This text is long and has been trimmed here. Open the source document for the complete record.
This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.