# 87 FR 8509: Endangered and Threatened Wildlife and Plants; Endangered Species for Prostrate Milkweed and Designation of Critical Habitat

> Federal · Regulations · In force

URL: https://www.frixlaw.com/law-library/statutes/FR_PRORULE_2022-02544

## Section

- **Citation:** 87 FR 8509
- **Heading:** Endangered and Threatened Wildlife and Plants; Endangered Species for Prostrate Milkweed and Designation of Critical Habitat
- **Jurisdiction:** Federal
- **Kind:** Regulations
- **Status:** In force
- **Text as of:** August 14, 2026
- **Source:** Compiled text
- **Location:** Federal Register / Vol. 87 / 87 FR 8509

## Text

DEPARTMENT OF THE INTERIOR Fish and Wildlife Service 50 CFR Part 17 [Docket No. FWS-R2-ES-2021-0041; FF09E21000; FXES1111090FEDR 223] RIN 1018-BE65 Endangered and Threatened Wildlife and Plants; Endangered Species for Prostrate Milkweed and Designation of Critical Habitat AGENCY:
Fish and Wildlife Service, Interior.

ACTION:
Proposed rule.

SUMMARY:
We, the U.S. Fish and Wildlife Service (Service), propose to list the prostrate milkweed ( Asclepias prostrata ), a plant species from Texas, as an endangered species and designate critical habitat under the Endangered Species Act of 1973, as amended (Act). This determination also serves as our 12-month finding on a petition to list the prostrate milkweed. After a review of the best available scientific and commercial information, we find that listing the species is warranted. Accordingly, we propose to list the prostrate milkweed as an endangered species. If we finalize this rule as proposed, it would add this species to the List of Endangered and Threatened Plants and extend the Act's protections to the species. We also propose to designate critical habitat for the prostrate milkweed under the Act. In total, approximately 691.3 acres (279.8 hectares) in Starr and Zapata Counties, Texas, fall within the boundaries of the proposed critical habitat designation. We also announce the availability of a draft economic analysis of the proposed designation of critical habitat for prostrate milkweed.

DATES:
We will accept comments received or postmarked on or before April 18, 2022. Comments submitted electronically using the Federal eRulemaking Portal (see ADDRESSES , below) must be received by 11:59 p.m. Eastern Time on the closing date. We must receive requests for a public hearing, in writing, at the address shown in FOR FURTHER INFORMATION CONTACT by April 1, 2022.

ADDRESSES:
You may submit comments by one of the following methods:
ked on or before April 18, 2022. Comments submitted electronically using the Federal eRulemaking Portal (see ADDRESSES , below) must be received by 11:59 p.m. Eastern Time on the closing date. We must receive requests for a public hearing, in writing, at the address shown in FOR FURTHER INFORMATION CONTACT by April 1, 2022.

ADDRESSES:
You may submit comments by one of the following methods:
(1) Electronically: Go to the Federal eRulemaking Portal: https://www.regulations.gov. In the Search box, enter the docket number or RIN for this rulemaking (presented above in the document headings). For best results, do not copy and paste either number; instead, type the docket number or RIN into the Search box using hyphens. Then, click on the Search button. On the resulting page, in the panel on the left side of the screen, under the Document Type heading, check the Proposed Rule box to locate this document. You may submit a comment by clicking on “Comment.”
(2) By hard copy: Submit by U.S. mail to: Public Comments Processing, Attn: FWS-R2-ES-2021-0041, U.S. Fish and Wildlife Service, MS: PRB/3W, 5275 Leesburg Pike, Falls Church, VA 22041-3803.
We request that you send comments only by the methods described above. We will post all comments on https://www.regulations.gov. This generally means that we will post any personal information you provide us (see Information Requested, below, for more information).
Availability of supporting materials: The species status assessment report and the draft economic analysis are available at https://www.regulations.gov under Docket No. FWS-R2-ES-2021-0041. For the critical habitat designation, the coordinates or plot points or both from which the maps are generated are included in the decision file and are available at https://www.fws.gov/southwest/es/TexasCoastal/, at https://www.regulations.gov under Docket No. FWS-R2-ES-2021-0041, and at the Texas Coastal Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT )
FWS-R2-ES-2021-0041. For the critical habitat designation, the coordinates or plot points or both from which the maps are generated are included in the decision file and are available at https://www.fws.gov/southwest/es/TexasCoastal/, at https://www.regulations.gov under Docket No. FWS-R2-ES-2021-0041, and at the Texas Coastal Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT ). Any additional tools or supporting information that we may develop for the critical habitat designation will also be available at the Service website and field office set out above and may also be included in this preamble and/or at https://www.regulations.gov.
FOR FURTHER INFORMATION CONTACT:
Chuck Ardizzone, Field Supervisor, Texas Coastal Ecological Services Field Office, 17629 El Camino Real, Suite 211, Houston, TX 77058; telephone 281-286-8282. Persons who use a telecommunications device for the deaf (TDD) may call the Federal Relay Service at 800-877-8339.

SUPPLEMENTARY INFORMATION:
Executive Summary
Why we need to publish a rule. Under the Act, if we determine that a species warrants listing, we are required to promptly publish a proposal in the Federal Register , unless doing so is precluded by higher-priority actions and expeditious progress is being made to add and remove qualified species to or from the List of Endangered and Threatened Wildlife and Plants. The Service will make a determination on our proposal within 1 year. If there is substantial disagreement regarding the sufficiency and accuracy of the available data relevant to the proposed listing, we may extend the final determination for not more than six months. To the maximum extent prudent and determinable, we must designate critical habitat for any species that we determine to be an endangered or threatened species under the Act. Listing a species as an endangered or threatened species and designation of critical habitat can only be completed by issuing a rule.
What this document does
e may extend the final determination for not more than six months. To the maximum extent prudent and determinable, we must designate critical habitat for any species that we determine to be an endangered or threatened species under the Act. Listing a species as an endangered or threatened species and designation of critical habitat can only be completed by issuing a rule.
What this document does. We propose to list the prostrate milkweed as an endangered species under the Act, and we propose the designation of critical habitat for the species.
The basis for our action. Under the Act, we may determine that a species is an endangered or threatened species because of any of five factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) overutilization for commercial, recreational, scientific, or educational purposes; (C) disease or predation; (D) the inadequacy of existing regulatory mechanisms; or (E) other natural or manmade factors affecting its continued existence. We have determined that competition from introduced invasive grass; habitat loss and degradations from root-plowing and conversion of native vegetation to improved buffelgrass pasture; habitat loss from right of way (ROW) construction and maintenance from energy development and road and utility construction; habitat loss from border security development and enforcement activities (Factor A); and the demographic and genetic consequences of small population sizes (Factor E) are threats to the prostrate milkweed.
Section 4(a)(3) of the Act requires the Secretary of the Interior (Secretary) to designate critical habitat concurrent with listing to the maximum extent prudent and determinable
construction; habitat loss from border security development and enforcement activities (Factor A); and the demographic and genetic consequences of small population sizes (Factor E) are threats to the prostrate milkweed.
Section 4(a)(3) of the Act requires the Secretary of the Interior (Secretary) to designate critical habitat concurrent with listing to the maximum extent prudent and determinable. Section 3(5)(A) of the Act defines critical habitat as: (i) The specific areas within the geographical area occupied by the species, at the time it is listed, on which are found those physical or biological features (I) essential to the conservation of the species and (II) which may require special management considerations or protections; and (ii) specific areas outside the geographical area occupied by the species at the time it is listed, upon a determination by the Secretary that such areas are essential for the conservation of the species. Section 4(b)(2) of the Act states that the Secretary must make the designation on the basis of the best scientific data available and after taking into consideration the economic impact, the impact on national security, and any other relevant impacts of specifying any particular area as critical habitat.
Information Requested
We intend that any final action resulting from this proposed rule will be based on the best scientific and commercial data available and be as accurate and as effective as possible. Therefore, we request comments or information from other governmental
We particularly seek comments concerning:
(1) The species' biology, range, and population trends, including:
(a) Biological or ecological requirements of the species, including habitat requirements for feeding, breeding, and sheltering;
(b) Genetics and taxonomy;
(c) Historical and current range, including distribution patterns;
(d) Historical and current population levels, and current and projected trends; and
ents concerning:
(1) The species' biology, range, and population trends, including:
(a) Biological or ecological requirements of the species, including habitat requirements for feeding, breeding, and sheltering;
(b) Genetics and taxonomy;
(c) Historical and current range, including distribution patterns;
(d) Historical and current population levels, and current and projected trends; and
(e) Past and ongoing conservation measures for the species, its habitat, or both.
(2) Factors that may affect the continued existence of the species, which may include habitat modification or destruction, overutilization, disease, predation, the inadequacy of existing regulatory mechanisms, or other natural or manmade factors.
(3) Biological, commercial trade, or other relevant data concerning any threats (or lack thereof) to this species and existing regulations that may be addressing those threats.
(4) Additional information concerning the historical and current status, range, distribution, and population size of this species, including the locations of any additional populations of this species.
(5) The reasons why we should or should not designate habitat as “critical habitat” under section 4 of the Act (16 U.S.C. 1531 et seq. ), including information to inform the following factors that the regulations identify as reasons why designation of critical habitat may be not prudent:
(a) 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;
(b) The present or threatened destruction, modification, or curtailment of a species' habitat or range is not a threat to the species, or threats to the species' habitat stem solely from causes that cannot be addressed through management actions resulting from consultations under section 7(a)(2) of the Act;
f critical habitat can be expected to increase the degree of such threat to the species;
(b) The present or threatened destruction, modification, or curtailment of a species' habitat or range is not a threat to the species, or threats to the species' habitat stem solely from causes that cannot be addressed through management actions resulting from consultations under section 7(a)(2) of the Act;
(c) Areas within the jurisdiction of the United States provide no more than negligible conservation value, if any, for a species occurring primarily outside the jurisdiction of the United States; or
(d) No areas meet the definition of critical habitat.
(6) Specific information on:
(a) The amount and distribution of prostrate milkweed habitat;
(b) What areas, that are occupied at the time of listing and that contain the physical or biological features essential to the conservation of the species, should be included in the designation and why;
(c) Any additional areas occurring within the range of the species, including Starr and Zapata Counties, Texas, that should be included in the designation because they (1) are occupied at the time of listing and contain the physical or biological features that are essential to the conservation of the species and that may require special management considerations, or (2) are unoccupied at the time of listing and are essential for the conservation of the species;
(d) Special management considerations or protection that may be needed in critical habitat areas we are proposing, including managing for the potential effects of climate change; and
(e) What areas not occupied at the time of listing are essential for the conservation of the species. We particularly seek comments:
d at the time of listing and are essential for the conservation of the species;
(d) Special management considerations or protection that may be needed in critical habitat areas we are proposing, including managing for the potential effects of climate change; and
(e) What areas not occupied at the time of listing are essential for the conservation of the species. We particularly seek comments:
(i) Regarding whether occupied areas are adequate for the conservation of the species;
(ii) Providing specific information regarding whether or not unoccupied areas would, with reasonable certainty, contribute to the conservation of the species and contain at least one physical or biological feature essential to the conservation of the species; and
(iii) Explaining whether or not unoccupied areas fall within the definition of “habitat” at 50 CFR 424.02 and why.
(7) Land use designations and current or planned activities in the subject areas and their possible impacts on proposed critical habitat.
(8) Any probable economic, national security, or other relevant impacts of designating any area that may be included in the final designation, and the related benefits of including or excluding specific areas.
(9) Information on the extent to which the description of probable economic impacts in the draft economic analysis is a reasonable estimate of the likely economic impacts and any additional information regarding probable economic impacts that we should consider.
designating any area that may be included in the final designation, and the related benefits of including or excluding specific areas.
(9) Information on the extent to which the description of probable economic impacts in the draft economic analysis is a reasonable estimate of the likely economic impacts and any additional information regarding probable economic impacts that we should consider.
(10) Whether any specific areas we are proposing for critical habitat designation should be considered for exclusion under section 4(b)(2) of the Act, and whether the benefits of potentially excluding any specific area outweigh the benefits of including that area under section 4(b)(2) of the Act, in particular for the critical habitat units on privately owned lands. If you think we should exclude any additional areas, please provide credible information regarding the existence of a meaningful economic or other relevant impact supporting a benefit of exclusion.
(11) Whether we could improve or modify our approach to designating critical habitat in any way to provide for greater public participation and understanding, or to better accommodate public concerns and comments.
Please include sufficient information with your submission (such as scientific journal articles or other publications) to allow us to verify any scientific or commercial information you include.
Please note that submissions merely stating support for, or opposition to, the action under consideration without providing supporting information, although noted, will not be considered in making a determination, as section 4(b)(1)(A) of the Act directs that determinations as to whether any species is an endangered or a threatened species must be made “solely on the basis of the best scientific and commercial data available.”
You may submit your comments and materials concerning this proposed rule by one of the methods listed in ADDRESSES . We request that you send comments only by the methods described in ADDRESSES
b)(1)(A) of the Act directs that determinations as to whether any species is an endangered or a threatened species must be made “solely on the basis of the best scientific and commercial data available.”
You may submit your comments and materials concerning this proposed rule by one of the methods listed in ADDRESSES . We request that you send comments only by the methods described in ADDRESSES .
If you submit information via https://www.regulations.gov, your entire submission—including any personal identifying information—will be posted on the website. If your submission is made via a hardcopy that includes personal identifying information, you may request at the top of your document that we withhold this information from public review. However, we cannot guarantee that we will be able to do so. We will post all hardcopy submissions on https://www.regulations.gov.
Comments and materials we receive, as well as supporting documentation we used in preparing this proposed rule, will be available for public inspection on https://www.regulations.gov.
Because we will consider all comments and information we receive during the comment period, our final determinations may differ from this proposal. Based on the new information we receive (and any comments on that new information), we may conclude that the species is threatened instead of endangered, or we may conclude that the species does not warrant listing as either an endangered species or a threatened species. For critical habitat, our final designation may not include all areas proposed, may include some additional areas that meet the definition
Public Hearing
Section 4(b)(5) of the Act provides for a public hearing on this proposal, if requested. Requests must be received by the date specified in DATES . Such requests must be sent to the address shown in FOR FURTHER INFORMATION CONTACT
d species. For critical habitat, our final designation may not include all areas proposed, may include some additional areas that meet the definition
Public Hearing
Section 4(b)(5) of the Act provides for a public hearing on this proposal, if requested. Requests must be received by the date specified in DATES . Such requests must be sent to the address shown in FOR FURTHER INFORMATION CONTACT . We will schedule a public hearing on this proposal, if requested, and announce the date, time, and place of the hearing, as well as how to obtain reasonable accommodations, in the Federal Register and local newspapers at least 15 days before the hearing. For the immediate future, we will provide these public hearings using webinars that will be announced on the Service's website, in addition to the Federal Register . The use of these virtual public hearings is consistent with our regulations at 50 CFR 424.16(c)(3).
Previous Federal Actions
On June 25, 2007, we received a petition, dated June 18, 2007, from Forest Guardians (now WildEarth Guardians) that included the prostrate milkweed. On December 16, 2009, we published a 90-day finding (74 FR 66866) that the petition presented substantial information that prostrate milkweed may be warranted for listing. At that time, we initiated a status review of the species.
Supporting Documents
A species status assessment (SSA) team prepared an SSA report for the prostrate milkweed. The SSA team was composed of Service biologists, in consultation with other species experts. The SSA report represents a compilation of the best scientific and commercial data available concerning the status of the species, including the impacts of past, present, and future factors (both negative and beneficial) affecting the species
nt (SSA) team prepared an SSA report for the prostrate milkweed. The SSA team was composed of Service biologists, in consultation with other species experts. The SSA report represents a compilation of the best scientific and commercial data available concerning the status of the species, including the impacts of past, present, and future factors (both negative and beneficial) affecting the species. In accordance with our joint policy on peer review published in the Federal Register on July 1, 1994 (59 FR 34270), and our August 22, 2016, memorandum updating and clarifying the role of peer review of listing actions under the Act, we sought the expert opinions of six appropriate specialists regarding the SSA report. The Service received two responses. The Service also sent the SSA report to one partner, a botanist from the Texas Parks and Wildlife Department, and received a review from this partner.
I. Proposed Listing Determination
Background
A thorough review of the taxonomy, life history, and ecology of the prostrate milkweed ( Asclepias prostrata ) is presented in the SSA report (Service 2020, entire). Prostrate milkweed is an herbaceous, flowering plant in the Apocynaceae (dogbane) family. It is native to Texas, USA, and Tamaulipas and eastern Nuevo León, Mexico.
Prostrate milkweed is a perennial species with cream, yellow, greenish, or pinkish flowers (Blackwell 1964, p. 178). This species is distinctive in its prostrate habit; the leaves and stems sprawl outward along the surface of the ground. It is found in open spaces with full sun, and with little to no competition from surrounding plants (Poole and Janssen 1997, p. 117). It occurs in a subtropical, semiarid climate in sparsely vegetated habitats, including grasslands, savannas, and open areas of the Tamaulipan shrubland ecological region, on level or gently sloping uplands (Singhurst et al. 2015, p. 25; Carr 2011, pp. 37-38; Damude and Poole 1990, p. 13; Strong and Williamson 2015, p. 36)
to no competition from surrounding plants (Poole and Janssen 1997, p. 117). It occurs in a subtropical, semiarid climate in sparsely vegetated habitats, including grasslands, savannas, and open areas of the Tamaulipan shrubland ecological region, on level or gently sloping uplands (Singhurst et al. 2015, p. 25; Carr 2011, pp. 37-38; Damude and Poole 1990, p. 13; Strong and Williamson 2015, p. 36). Prostrate milkweed occurs primarily in deep, loose, sandy soils formed over sandstone or indurated caliche (hardened soil layer cemented by calcium and magnesium carbonates) (Carr 2011, pp. 37-38; Strong and Williamson 2015, p. 36).
Like all milkweeds, prostrate milkweed flowers have a unique and complex structure and pollination system. Pollinators are attracted to the copious nectar produced deep within the flower. To reach the nectar, insects of a particular size are forced against the flower's central stalk in such a way that pollinia, which are sack-like structures full of pollen grains, adhere to their legs. When the insect visits another flower of the same species, the pollinia are often wedged against the stigma (the receptive female structure) and detach, thus delivering a large load of pollen and effecting fertilization. The closely-related zizotes milkweed, Asclepias oenotheroides, is effectively pollinated by very large wasps called tarantula hawks (species of Pepsis and Hemipepsis ), and it is likely that these wasps and large bees also pollinate prostrate milkweed. Due to their relatively large size and the abundance of nectar produced by the flowers, these pollinators are able to fly relatively large distances between nectar sources (Gathman and Tscharntke 2002, entire; Greenleaf et al. 2007, entire). Hence, it is likely that prostrate milkweed can reproduce even when individuals are widely distributed at very low densities, due to the uniquely effective pollination system, large nectar reward, and large forage range of its pollinators
lowers, these pollinators are able to fly relatively large distances between nectar sources (Gathman and Tscharntke 2002, entire; Greenleaf et al. 2007, entire). Hence, it is likely that prostrate milkweed can reproduce even when individuals are widely distributed at very low densities, due to the uniquely effective pollination system, large nectar reward, and large forage range of its pollinators.
Fertilized flowers of prostrate milkweed produce capsules with about 100 seeds each. The seeds have long, silky, white hairs and are dispersed by wind (Damude and Poole 1990, pp. 4-5; Richardson and King 2011, p. 76). Seed production of milkweeds is often resource limited (La Rosa and Conner 2017, p. 151); resources for prostrate milkweed include rainfall, pollinators, and open, sparsely vegetated habitat.
Prostrate milkweed remains as tubers, up to 12 inches (in) (30 centimeters (cm)) underground that are dormant during long droughts. New stems are stimulated to emerge from the soil by infrequent, heavy rainfall, and set seed following wildfire or, historically, a passing herd of bison has cleared competing grasses and forbs, and the deluges of tropical storms briefly replenish moisture. The species exists where competition from other plants is periodically reduced by wildfire or grazing. These life-history traits allow the species to rebound after periods of inhospitable conditions, and well-managed livestock grazing, which simulates the effects of bison, and rangeland management, including brush thinning and prescribed burning, can return an unsuitable area to conditions more suitable for prostrate milkweed. As a result, sufficiently resilient prostrate milkweed populations may be maintained on well-managed rangelands. Livestock grazing is the primary economic use of privately-owned land throughout the range of prostrate milkweed in Texas and northeast Mexico, although the management regime of these rangelands is unknown
can return an unsuitable area to conditions more suitable for prostrate milkweed. As a result, sufficiently resilient prostrate milkweed populations may be maintained on well-managed rangelands. Livestock grazing is the primary economic use of privately-owned land throughout the range of prostrate milkweed in Texas and northeast Mexico, although the management regime of these rangelands is unknown. This adaptation also enables prostrate milkweed to occur along mowed road rights-of-way (ROWs) and in rangelands where soils are intact. Therefore, while there may be prostrate milkweed populations on these rangelands, we do not have evidence that they are present, nor do we have information that the grazing is managed in such a way as to promote resilient populations. However, it is unlikely to remain where soils are disturbed by plowing, bulldozing, or road grading because this destroys the tubers, preventing any plant regrowth.
In the United States, prostrate milkweed occurs in south Texas from northwest Zapata County to the vicinity of Roma, in Starr County. All known U.S. populations are within 8 miles of the Rio Grande (Strong and Williamson 2015, pp. 34-35). In Mexico, known locations for this species occur in
Regulatory and Analytical Framework
Regulatory Framework
Section 4 of the Act (16 U.S.C. 1533) and its implementing regulations (50 CFR part 424) set forth the procedures for determining whether a species is an endangered species or a threatened species
pulations are within 8 miles of the Rio Grande (Strong and Williamson 2015, pp. 34-35). In Mexico, known locations for this species occur in
Regulatory and Analytical Framework
Regulatory Framework
Section 4 of the Act (16 U.S.C. 1533) and its implementing regulations (50 CFR part 424) set forth the procedures for determining whether a species is an endangered species or a threatened species. The Act defines an endangered species as a species that is “in danger of extinction throughout all or a significant portion of its range,” and a threatened species as a species that is “likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.” The Act requires that we determine whether any species is an endangered species or a threatened species because of any of the following factors:
(A) The present or threatened destruction, modification, or curtailment of its habitat or range;
(B) Overutilization for commercial, recreational, scientific, or educational purposes;
(C) Disease or predation;
(D) The inadequacy of existing regulatory mechanisms; or
(E) Other natural or manmade factors affecting its continued existence.
These factors represent broad categories of natural or human-caused actions or conditions that could have an effect on a species' continued existence. In evaluating these actions and conditions, we look for those that may have a negative effect on individuals of the species, as well as other actions or conditions that may ameliorate any negative effects or may have positive effects.
We use the term “threat” to refer in general to actions or conditions that are known to or are reasonably likely to negatively affect individuals of a species. The term “threat” includes actions or conditions that have a direct impact on individuals (direct impacts), as well as those that affect individuals through alteration of their habitat or required resources (stressors)
e positive effects.
We use the term “threat” to refer in general to actions or conditions that are known to or are reasonably likely to negatively affect individuals of a species. The term “threat” includes actions or conditions that have a direct impact on individuals (direct impacts), as well as those that affect individuals through alteration of their habitat or required resources (stressors). The term “threat” may encompass—either together or separately—the source of the action or condition or the action or condition itself.
However, the mere identification of any threat(s) does not necessarily mean that the species meets the statutory definition of an “endangered species” or a “threatened species.” In determining whether a species meets either definition, we must evaluate all identified threats by considering the expected response by the species, and the effects of the threats—in light of those actions and conditions that will ameliorate the threats—on an individual, population, and species level. We evaluate each threat and its expected effects on the species, then analyze the cumulative effect of all of the threats on the species as a whole. We also consider the cumulative effect of the threats in light of those actions and conditions that will have positive effects on the species, such as any existing regulatory mechanisms or conservation efforts. The Secretary determines whether the species meets the definition of an “endangered species” or a “threatened species” only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.
The Act does not define the term “foreseeable future,” which appears in the statutory definition of “threatened species.” Our implementing regulations at 50 CFR 424.11(d) set forth a framework for evaluating the foreseeable future on a case-by-case basis
ed species” only after conducting this cumulative analysis and describing the expected effect on the species now and in the foreseeable future.
The Act does not define the term “foreseeable future,” which appears in the statutory definition of “threatened species.” Our implementing regulations at 50 CFR 424.11(d) set forth a framework for evaluating the foreseeable future on a case-by-case basis. The term “foreseeable future” extends only so far into the future as the Service can reasonably determine that both the future threats and the species' responses to those threats are likely. In other words, the foreseeable future is the period of time in which we can make reliable predictions. “Reliable” does not mean “certain”; it means sufficient to provide a reasonable degree of confidence in the prediction. Thus, a prediction is reliable if it is reasonable to depend on it when making decisions.
It is not always possible or necessary to define foreseeable future as a particular number of years. Analysis of the foreseeable future uses the best scientific and commercial data available and should consider the timeframes applicable to the relevant threats and to the species' likely responses to those threats in view of its life-history characteristics. Data that are typically relevant to assessing the species' biological response include species-specific factors such as lifespan, reproductive rates or productivity, certain behaviors, and other demographic factors.
Analytical Framework
The SSA report documents the results of our comprehensive biological review of the best scientific and commercial data regarding the status of the species, including an assessment of the potential threats to the species. The SSA report does not represent a decision by the Service on whether the species should be proposed for listing as an endangered or threatened species under the Act
Framework
The SSA report documents the results of our comprehensive biological review of the best scientific and commercial data regarding the status of the species, including an assessment of the potential threats to the species. The SSA report does not represent a decision by the Service on whether the species should be proposed for listing as an endangered or threatened species under the Act. However, it does provide the scientific basis that informs our regulatory decisions, which involve the further application of standards within the Act and its implementing regulations and policies. The following is a summary of the key results and conclusions from the SSA report; the full SSA report can be found at Docket FWS-R2-ES-2021-0041 on https://www.regulations.gov and at https://www.fws.gov/southwest/es/TexasCoastal/.
To assess prostrate milkweed viability, we used the three conservation biology principles of resiliency, redundancy, and representation (Shaffer and Stein 2000, pp. 306-310). Briefly, resiliency supports the ability of the species to withstand environmental and demographic stochasticity (for example, wet or dry, warm or cold years), redundancy supports the ability of the species to withstand catastrophic events (for example, droughts, large pollution events), and representation supports the ability of the species to adapt over time to long-term changes in the environment (for example, climate changes). In general, the more resilient and redundant a species is and the more representation it has, the more likely it is to sustain populations over time, even under changing environmental conditions. Using these principles, we identified the species' ecological requirements for survival and reproduction at the individual, population, and species levels, and described the beneficial and risk factors influencing the species' viability.
The SSA process can be categorized into three sequential stages. During the first stage, we evaluated the individual species' life-history needs
tal conditions. Using these principles, we identified the species' ecological requirements for survival and reproduction at the individual, population, and species levels, and described the beneficial and risk factors influencing the species' viability.
The SSA process can be categorized into three sequential stages. During the first stage, we evaluated the individual species' life-history needs. The next stage involved an assessment of the historical and current condition of the species' demographics and habitat characteristics, including an explanation of how the species arrived at its current condition. The final stage of the SSA involved making predictions about the species' responses to positive and negative environmental and anthropogenic influences. Throughout all of these stages, we used the best available information to characterize viability as the ability of a species to
Summary of Biological Status and Threats
In this discussion, we review the biological condition of the species and its resources, and the threats that influence the species' current and future condition, in order to assess the species' overall viability and the risks to that viability.
For the prostrate milkweed to maintain viability, its populations or some portion thereof must have sufficient resiliency, redundancy, and representation. Several factors influence the resiliency of prostrate milkweed populations, including abundance and recruitment rate, in addition to elements of the species' habitat that determine whether prostrate milkweed populations can grow. These resiliency factors and habitat elements are discussed in detail in the SSA report and summarized here.
Species Needs
Abundance—Prostrate milkweed abundance is difficult to assess due to its ability to remain dormant for multiple years until the necessary environmental conditions occur. Individual plants may emerge only a few times per decade, and not all plants will emerge at the same time (Price 2005, pers. comm.; Best 2017, pers. comm.)
scussed in detail in the SSA report and summarized here.
Species Needs
Abundance—Prostrate milkweed abundance is difficult to assess due to its ability to remain dormant for multiple years until the necessary environmental conditions occur. Individual plants may emerge only a few times per decade, and not all plants will emerge at the same time (Price 2005, pers. comm.; Best 2017, pers. comm.). Therefore, we considered populations to be extant if plants have been observed within the past 40 years (Hammerson et al. 2008, entire; Strong 2020, pers. comm.) and with available habitat ( i.e., not paved over) or with restorable habitat ( i.e., nonnative grass could be removed).
Populations of prostrate milkweed must be large enough to have a high probability of enduring random demographic and environmental variation. For example, species or populations may be classified as vulnerable when the probability of persisting 100 years is less than 90 percent (Mace and Lande 1991, p. 151). This metric of population resilience, called minimum viable population (MVP), refers to the smallest population size that has a high probability of surviving over a specified period of time. Calculations of MVP require data that are not currently available for prostrate milkweed. As a practical alternative, we estimated the likely MVP range of prostrate milkweed by comparing it to species with similar life-history traits for which MVPs have been calculated (Pavlik 1996, p. 137). This method estimates a highly resilient population of prostrate milkweed has 1,600 or more adult individuals (Service 2020, p. 38).
Determinations of MVP usually consider the effective population size, rather than total number of individuals (Pavlik 1996, entire); 10 genetically identical individuals (for example, clones or ramets) would have an effective population size of one
k 1996, p. 137). This method estimates a highly resilient population of prostrate milkweed has 1,600 or more adult individuals (Service 2020, p. 38).
Determinations of MVP usually consider the effective population size, rather than total number of individuals (Pavlik 1996, entire); 10 genetically identical individuals (for example, clones or ramets) would have an effective population size of one. Because prostrate milkweed is likely self-incompatible and does not appear to form clonal colonies, the effective population size is likely to be nearly the same as the total population size.
Recruitment Rate—A stable or increasing population requires recruitment rates that equal or exceed mortality rates (Service 2020, p. 38). All stages of recruitment, from flowering and seed production to germination and establishment, occur when the soil has available moisture. The porous soils of prostrate milkweed habitat dry quickly after a single heavy thunderstorm. Based on observations of other perennial forbs in this ecosystem, recruitment probably occurs during periods of extended rainfall, meaning multiple rain events over a period of several weeks (Service 2020, p. 38). These events are rare in this semiarid region. Consequently, we expect that successful recruitment may occur only once or a few times per decade. Similarly, most mortality probably occurs during years of extended drought. Hence, both recruitment and mortality would have strong pulses and observed population sizes would vary widely from year to year, leading to potentially spurious interpretations of demographic trends (Service 2020, p. 38).
Populations of prostrate milkweed require habitats that also support healthy populations of large native bees and wasps (Service 2020, p. 38). Native bees in turn require a diversity and abundance of native forb and shrub species that provide pollen and nectar. Tarantula hawks ( Pepsis spp
year to year, leading to potentially spurious interpretations of demographic trends (Service 2020, p. 38).
Populations of prostrate milkweed require habitats that also support healthy populations of large native bees and wasps (Service 2020, p. 38). Native bees in turn require a diversity and abundance of native forb and shrub species that provide pollen and nectar. Tarantula hawks ( Pepsis spp. and Hemipepsis spp.) may also be important pollinators of prostrate milkweed; tarantula hawks require healthy populations of their prey species, tarantulas (Best 2020, pers. comm.).
Prostrate milkweed populations require competition from grasses and forbs to be periodically reduced (Service 2020, p. 38). This requirement, which has been observed in other milkweed species, may be an adaptation to wildfire (Baum and Sharber 2012, pp. 968-971). Although mowing or livestock grazing can also reduce competition, it is likely that prostrate milkweed is adapted to grasslands that were sustained by periodic wildfires (Service 2020, p. 39).
Canopy Cover—Canopy cover refers to shade from trees, shrubs, prickly pear cactuses, or tall (>1 meter (m)) grass. Resilient prostrate milkweed populations need an open canopy with little or no herbaceous cover (Service 2020, p. 3). Therefore, the species may occur in areas that mimic historical wildfire or grazing, such as along mowed road rights-of-way (Service 2020, p. 3).
Ground Cover—Ground cover refers to vegetation growing at the herbaceous layer (approximately <1 m) that would compete with prostrate milkweed plants for resources. Resilient prostrate milkweed populations need an open canopy with little or no herbaceous cover, so there is little competition with other plants (Service 2020, p. 3).
Risk Factors for Prostrate Milkweed
We reviewed the potential risk factors ( i.e., threats, stressors) that may affect prostrate milkweed now and in the future
m) that would compete with prostrate milkweed plants for resources. Resilient prostrate milkweed populations need an open canopy with little or no herbaceous cover, so there is little competition with other plants (Service 2020, p. 3).
Risk Factors for Prostrate Milkweed
We reviewed the potential risk factors ( i.e., threats, stressors) that may affect prostrate milkweed now and in the future. In this proposed rule, we will discuss only those factors in detail that could meaningfully impact the status of the species. Those risks that are not known to have effects on prostrate milkweed populations, such as quarrying/mining, hybridization, pollinator decline, and climate change, are not discussed here but are evaluated in the SSA report. The primary risk factors ( i.e., threats) affecting the status of prostrate milkweed are: (1) Competition from introduced invasive grasses (Factor A from the Act); (2) habitat loss from root-plowing and conversion of native vegetation to pasture (Factor A); (3) habitat loss from ROW construction and maintenance from energy development and road and utility construction (Factor A); (4) habitat loss from border security development and enforcement activities (Factor A); and (5) the demographic and genetic consequences of small population sizes and population fragmentation (Factor E).
Competition From Nonnative Invasive Grasses
Nonnative invasive grass species displace native plants by competing for water, nutrients, and light, and their dense root systems prevent germination of native plant seeds (Texas Invasives 2019, unpaginated). Buffelgrass ( Pennisetum ciliare ) is a perennial bunchgrass introduced from Africa that is now one of the most abundant introduced grasses in south Texas, and the most prevalent invasive grass within the range of prostrate milkweed. Since the 1950s, Federal and State land management agencies have promoted buffelgrass as a forage grass in south et al. 2013, p
s (Texas Invasives 2019, unpaginated). Buffelgrass ( Pennisetum ciliare ) is a perennial bunchgrass introduced from Africa that is now one of the most abundant introduced grasses in south Texas, and the most prevalent invasive grass within the range of prostrate milkweed. Since the 1950s, Federal and State land management agencies have promoted buffelgrass as a forage grass in south et al. 2013, p. 8), and it produces phytotoxins in the soil that inhibit the growth of neighboring native plants (Vo 2013, unpaginated). Furthermore, prescribed burning used for brush control promotes buffelgrass forage production in south Texas (Hamilton and Scifres 1982, p. 11).
Most prostrate milkweed plants have been observed where buffelgrass is absent or at low densities (Eason 2019, pers. comm.; Strong 2019, pers. comm.). On national wildlife refuge lands, prostrate milkweed was found in areas where native grass was still dominant, but not where buffelgrass or woody vegetation was present in dense stands (Best 2005, p. 3). The unpaved ROWs on private lands in south Texas for oil and gas wells, wind farms, service roads, pipelines, and powerlines could benefit prostrate milkweed through the periodic mowing of road margins. However, disturbed soils along ROWs are rapidly colonized by buffelgrass.
The Texas Natural Diversity Database (TXNDD) lists invasive species, primarily buffelgrass, as a pervasive threat of extreme severity to prostrate milkweed. The TXNDD defines a pervasive threat as one that affects all or most (71-100 percent) of a species' populations, occurrences, or extent. An extreme level of severity is one that is likely to destroy or eliminate occurrences or habitat or reduce population sizes by 71-100 percent (TXNDD 2016). It is likely that buffelgrass has negatively impacted all Texas populations (TXNDD 2019-2020, entire; Eason 2019, pers. comm.; Kieschnick 2019, pers. comm.; Santore 2019, unpaginated). Competition from buffelgrass is the greatest threat to prostrate milkweed
l of severity is one that is likely to destroy or eliminate occurrences or habitat or reduce population sizes by 71-100 percent (TXNDD 2016). It is likely that buffelgrass has negatively impacted all Texas populations (TXNDD 2019-2020, entire; Eason 2019, pers. comm.; Kieschnick 2019, pers. comm.; Santore 2019, unpaginated). Competition from buffelgrass is the greatest threat to prostrate milkweed.
Root-Plowing and Conversion of Native Grassland and Savanna
Root-plowing is a brush control method that uses powerful tracked vehicles to excavate the roots of woody plants with heavy steel subsoil rippers that dig several feet into the ground. The dead trees and shrubs are then burned, and the root-plowed soils are planted with buffelgrass for livestock grazing. Root-plowing and conversion to buffelgrass pasture is a widely conducted practice in south Texas and northeast Mexico, occurring in much of the potential habitat of prostrate milkweed. Extensive areas of recently root-plowed lands can be identified in aerial photographs. These practices have been and are still subsidized by the United States Department of Agriculture (USDA) Natural Resources Conservation Service and its precursor, the USDA Soil Conservation Service.
Root-plowing temporarily reduces the encroachment of woody plants into the grassland component of former savannas. The conversion of native habitats to improved pastures dominated by buffelgrass or other introduced grasses greatly reduces the abundance and diversity of most native grass and forb species (Woodin et al. 2010, p. 1). Very few, if any, prostrate milkweed plants survive following root-plowing and buffelgrass planting. This is likely due to the excavation and desiccation of most tubers during root-plowing; subsequently, the few remaining individuals decline due to competition from dense buffelgrass cover.
Conversely, prostrate milkweed occurs in well-managed rangelands, provided that the soil was not previously root-plowed or otherwise disturbed (Service 2020, p. 53)
wing root-plowing and buffelgrass planting. This is likely due to the excavation and desiccation of most tubers during root-plowing; subsequently, the few remaining individuals decline due to competition from dense buffelgrass cover.
Conversely, prostrate milkweed occurs in well-managed rangelands, provided that the soil was not previously root-plowed or otherwise disturbed (Service 2020, p. 53). Most milkweed species are unpalatable to cattle, and often increase in abundance on grazed lands. Livestock, including cattle, sheep, and horses, graze preferentially on grasses and forbs (broad-leaved herbaceous plants), including buffelgrass, and non-toxic herbaceous plants, and therefore reduce competition with prostrate milkweed from these plants (Service 2020, p. 41). In addition to grazing, livestock may also reduce competition with prostrate milkweed by trampling herbaceous plants (Service 2020, p. 41). Because prostrate milkweed is often observed in the wheel ruts of dirt roads, it appears to be unusually tolerant of trampling; thus, the effect of livestock trampling is minimal (Service 2020, pp. 41-42). Periodic livestock grazing reduces competition from native and introduced grasses. In South Texas, over-grazed rangelands typically become invaded by woody plants, reducing the habitat suitability for prostrate milkweed. Hence, management practices that promote sustainable grazing of native grasses are beneficial to prostrate milkweed (Service 2020, p. 41).
Road and ROW Construction and Maintenance
Oil and gas exploration and wind energy development are occurring at a rapid pace in Starr and Zapata Counties. Seismic exploration and the construction of roads and caliche pads for oil and gas wells and wind turbines can destroy plants and their habitats within the construction footprint (Reemts et al. 2014, pp. 123 and 125; Leslie 2016, p. 49)
41).
Road and ROW Construction and Maintenance
Oil and gas exploration and wind energy development are occurring at a rapid pace in Starr and Zapata Counties. Seismic exploration and the construction of roads and caliche pads for oil and gas wells and wind turbines can destroy plants and their habitats within the construction footprint (Reemts et al. 2014, pp. 123 and 125; Leslie 2016, p. 49). Additionally, graded service roads and other permanent structures may indirectly affect the hydrology of surrounding habitats by diverting and channeling water through drainage culverts. Invasive buffelgrass quickly colonizes disturbed roadsides, then invades adjacent habitats. Heavy vehicle traffic during oil and gas well drilling and wind farm construction may increase the frequency of road maintenance, such as grading or widening (Peña 2019, pers. comm.). Grading or blading a caliche road involves scraping the road's surface with a large heavy blade to remove ruts and roadside vegetation. Increased frequency of road maintenance that removes above-ground portions of plants could reduce or eliminate prostrate milkweed flower and fruit production. Conversely, grading or blading of caliche roads conducted during the milkweed's dormant periods may benefit the species by temporarily reducing competition from grasses and forbs (TXNDD 2019, p. 11). TXNDD (2019) ranks road expansion as a pervasive threat (affects all or most (71-100 percent) of a species' populations, occurrences, or extent) of extreme severity to prostrate milkweed.
All or parts of nine prostrate milkweed occurrences are in the margins of improved highway ROWs. All of these highway ROW populations have declined since they were first observed, likely due to the frequency of soil disturbance and invasive grass competition (Service 2020, p. 40). In addition, from 2010 to 2012, Texas Department of Transportation (TxDOT) widened segments of U.S
ostrate milkweed.
All or parts of nine prostrate milkweed occurrences are in the margins of improved highway ROWs. All of these highway ROW populations have declined since they were first observed, likely due to the frequency of soil disturbance and invasive grass competition (Service 2020, p. 40). In addition, from 2010 to 2012, Texas Department of Transportation (TxDOT) widened segments of U.S. Highway 83 that affected at least three known prostrate milkweed sites: Arroyo del Tigre Grande, Mission Mier a Visita, and Arroyo Roma (Strong and Williamson 2015, p. 51; Paradise 2019, pers. comm.). TxDOT has also scheduled additional road widening or construction at five known prostrate milkweed populations: Arroyo del Tigre Grande, Arroyo del Tigre Chiquito, Arroyo de los Mudos, Mission Mier a Visita, and Arroyo Roma (TxDOT 2019, unpaginated). U.S. Customs and Border Protection (CBP) has scheduled road
In contrast, all or parts of three prostrate milkweed occurrences are in the margins of unpaved rural roads. These relatively stable populations have persisted in narrow strips of native vegetation between the gravel or caliche roadbeds and the fence lines of adjacent private properties. The soils in these narrow, naturally vegetated strips have never been excavated, and they have relatively little buffelgrass cover.
The installation of natural gas pipelines and fiber-optic cables has removed prostrate milkweed plants in the Dolores and Arroyo del Tigre Chiquito populations in the past (Damunde and Poole 1990, p. 32; Boydston 1993, unpaginated; Campos 1993, unpaginated). In 1995, Southwestern Bell installed a fiber-optic cable in the Highway 83 ROW, 2.6 miles south of the Webb-Zapata County line, which removed at least 100 individuals at the Dolores population (Service 1995, p. 1). In 1993, prior to the fiber-optic cable installation, this population was estimated to have 100 to 200 individuals (TXNDD 2019, entire) and was the largest known population of prostrate milkweed
Southwestern Bell installed a fiber-optic cable in the Highway 83 ROW, 2.6 miles south of the Webb-Zapata County line, which removed at least 100 individuals at the Dolores population (Service 1995, p. 1). In 1993, prior to the fiber-optic cable installation, this population was estimated to have 100 to 200 individuals (TXNDD 2019, entire) and was the largest known population of prostrate milkweed.
In summary, prostrate milkweed faces risks from ROWs and road construction and maintenance associated with oil and gas activities, wind energy development, and utility and pipeline corridor construction.
Border Security Development and Enforcement Activities
All known Texas populations of prostrate milkweed are within 9 miles (14.5 km) of the Texas-Mexico border. To address border security concerns, additional border barrier construction was proposed in the Rio Grande Valley, including the Arroyo Morteros tract of the Lower Rio Grande Valley NWR. Should border wall construction occur, and depending on the alignment, construction could remove prostrate milkweed plants that occur within the construction footprint. Additionally, CBP plans to improve roads across this tract (Vallejo 2019, pers. comm.) and may also install new drag strips along existing roads. Drag strips are 13- to 16-foot (ft) (4- to 5-m) -wide swaths cleared of all vegetation and regularly scraped to keep the soil surface loose, in order to detect recent foot traffic. Due to the high gypsum content, soils in this area are extremely vulnerable to gully erosion. Hence, the unvegetated, continually disturbed drag strips may exacerbate soil erosion and impact a much wider area. TXNDD ranks drag strip construction within prostrate milkweed populations as a small threat (defined as a threat that affects 1-10 percent of the total population or occurrences or extent) with an extreme level of severity (likely to destroy or eliminate occurrences or habitat, or reduce population by 71-100 percent) (TXNDD 2016)
rag strips may exacerbate soil erosion and impact a much wider area. TXNDD ranks drag strip construction within prostrate milkweed populations as a small threat (defined as a threat that affects 1-10 percent of the total population or occurrences or extent) with an extreme level of severity (likely to destroy or eliminate occurrences or habitat, or reduce population by 71-100 percent) (TXNDD 2016). Consequently, the construction of border barriers, roads, and drag strips are potential threats of high magnitude to prostrate milkweed populations, depending on their alignment, design, and proximity to populations and local topography.
Native plant populations are legally protected on NWRs and, if listed under the Act, have additional legal protections from federally funded or regulated actions. However, a provision of the REAL ID Act of 2005 gives the Secretary of Homeland Security authority to waive other Federal laws, including the Endangered Species Act, in order to expedite construction of border barriers. Therefore, border barrier construction on private and public lands is exempt from consultation with the Service under section 7 of the Act. During the previous phase of border barrier construction, beginning in 2007, the Department of Homeland Security (DHS) and the Service coordinated to establish best management practices for the federally listed plants and animals in the project impact area (DHS 2008); nevertheless, these best management practices did not address prostrate milkweed.
Small Population Sizes and Population Fragmentation
Small, isolated populations are more vulnerable to catastrophic losses caused by random fluctuations in recruitment (demographic stochasticity) or variations in rainfall or other environmental factors (environmental stochasticity) (Service 2016, p. 20). Small, reproductively isolated populations are susceptible to the loss of genetic diversity, to genetic drift, and to inbreeding (Barrett and Kohn 1991, pp. 3-30)
potential habitat on private lands, may represent only tiny fractions of larger, highly dispersed populations (Service 2020, p. 51).
Based strictly on the available scientific data, the documented populations of prostrate milkweed are all far below the estimated MVP level and may be affected by the demographic and genetic consequences of small population sizes and by fragmentation of populations.
Summary
Our analysis of the past, current, and future influences on the needs of prostrate milkweed for long-term viability revealed several threats that pose a risk to current and future viability: Competition from introduced invasive grass (buffelgrass); root-plowing of rangelands; development of new oil and gas wells, wind energy farms, roads, pipelines, and utility corridors; development of new border barriers and drag strips; and the demographic and genetic consequences of small population sizes and population fragmentation. Conversely, well-managed livestock grazing of rangeland is compatible with management of prostrate milkweed habitat and may actually benefit this species.
Species Condition
The current condition of prostrate milkweed takes into account the current status and risks to its populations. In the SSA report, for each population, we developed and assigned condition categories for two demographic factors and two habitat factors that are important for viability of prostrate milkweed. The condition scores for each factor were then used to estimate the probability of persistence over the next 30 years. Populations were rated high, moderate, or low when that probability is greater than 90 percent, between 60 and 90 percent, or between 10 and 60 percent, respectively. Functionally
There are 24 populations of prostrate milkweed remaining in Starr and Zapata Counties, Texas, and in Tamaulipas and eastern Nuevo León, Mexico (see Table 1, below). The species range extends more than 200 miles (320 kilometers) from northwest to southeast
, or low when that probability is greater than 90 percent, between 60 and 90 percent, or between 10 and 60 percent, respectively. Functionally
There are 24 populations of prostrate milkweed remaining in Starr and Zapata Counties, Texas, and in Tamaulipas and eastern Nuevo León, Mexico (see Table 1, below). The species range extends more than 200 miles (320 kilometers) from northwest to southeast. In Texas, one population, Dolores, is somewhat isolated in northern Zapata County, with the nearest known population approximately 25 miles (40 km) away. In Mexico, eight known populations are located in isolated pockets widely scattered in Tamaulipas and eastern Nuevo León. However, botanists have only surveyed a small proportion of the species' range. Furthermore, the species remains dormant and undetectable except for short periods of time after infrequent, heavy rainfall. Consequently, although the species is certainly rare, its actual abundance is difficult to determine. It is likely that, historically, populations occurred between these areas, connecting the populations in Texas and Mexico. Because they are widely separated, natural gene flow or reestablishment following disturbance is very unlikely between the 24 known populations. Based upon our analysis of current conditions of these 24 extant populations, none are in high condition, 5 are in moderate condition, and 19 are in low condition.
Table 1—Summary of Current Condition for Prostrate Milkweed Population name Current condition Dolores Low. 14493 Low. 14491 Low. Arroyo del Tigre Grande Moderate. Arroyo del Tigre Chiquito Low. FM 2098 Low. Falcon Low. Los Alvaros Moderate. Arroyo Morteros Tract Moderate. Los Arrieros Loop Low. Arroyo de los Mudos Low. Mission Mier a Visita Low. San Julián Road Moderate. FM 3167 Moderate. Arroyo Roma Low. Arroyo Ramirez Tract Low. Rancho La Coma Low. Road to Guerrero Viejo Low. Carboneras Low. Punta de Alambre Low. Intersection of 101-180 Low. Rio El Catán Low. Rancho Loreto North Low. Rancho Loreto South Low
w. Los Alvaros Moderate. Arroyo Morteros Tract Moderate. Los Arrieros Loop Low. Arroyo de los Mudos Low. Mission Mier a Visita Low. San Julián Road Moderate. FM 3167 Moderate. Arroyo Roma Low. Arroyo Ramirez Tract Low. Rancho La Coma Low. Road to Guerrero Viejo Low. Carboneras Low. Punta de Alambre Low. Intersection of 101-180 Low. Rio El Catán Low. Rancho Loreto North Low. Rancho Loreto South Low. The two demographic factors used to analyze resiliency of prostrate milkweed populations are abundance and recruitment rate. Related to abundance, a highly resilient population of prostrate milkweed has 1,600 or more adult individuals, a moderately resilient population has from 800 to 1,600 mature individuals, and a population with less than 800 mature individuals has low resilience (Service 2020, p. 38). Prostrate milkweed populations have high resiliency if the recruitment rate is greater than or equal to 25 percent of individuals producing viable seeds per year. Moderately resilient populations have recruitment rates of between 15 and 24 percent per year, and populations with low resiliency have recruitment rates of less than 15 percent per year (Service 2020, p. 57).
The two habitat factors used to analyze resiliency of prostrate milkweed populations were canopy cover and ground cover. Highly resilient populations have less than 30 percent canopy cover and have all bare ground or are sparsely vegetated with mostly native grass and/or forbs. Moderately resilient populations have between 30 and 60 percent canopy cover and are sparsely vegetated with a mixture of native and nonnative grasses and/or forbs. Minimally resilient populations have between 61 and 100 percent canopy cover and a dense ground cover of native or introduced grasses and forbs and little or no bare ground (Service 2020, p. 57).
Redundancy is low for this species due to low numbers of populations in moderate to high condition for resiliency, making prostrate milkweed populations vulnerable to extirpations from catastrophic events
nimally resilient populations have between 61 and 100 percent canopy cover and a dense ground cover of native or introduced grasses and forbs and little or no bare ground (Service 2020, p. 57).
Redundancy is low for this species due to low numbers of populations in moderate to high condition for resiliency, making prostrate milkweed populations vulnerable to extirpations from catastrophic events. Because buffelgrass invasion is prevalent in this area, ecological diversity among the known populations is limited. Further, the populations are isolated and widespread across the range, and therefore gene flow among the populations is limited. As a consequence of these current conditions, the viability of the prostrate milkweed now primarily depends on maintaining and restoring the remaining isolated populations and potentially discovering or reintroducing new populations where feasible.
As part of the SSA, we also developed three plausible future scenarios to capture the range of uncertainties regarding future threats and the projected responses by the prostrate milkweed. Our scenarios included a continuing conditions scenario, which incorporated the current risk factors continuing on the same trajectory that they are on now. We also evaluated a conservation scenario and a scenario with increased stressors. Because we determined that the current condition of the prostrate milkweed is consistent with an endangered species (see Determination of Species Status, below), we are not presenting the results of the future scenarios in this proposed rule. Please refer to the SSA report (Service 2020) for the full analysis of future scenarios.
We note that, by using the SSA framework to guide our analysis of the scientific information documented in the SSA report, we have not only analyzed individual effects on the species, but we have also analyzed their potential cumulative effects. We incorporate the cumulative effects into our SSA analysis when we characterize the current and future condition of the species
is of future scenarios.
We note that, by using the SSA framework to guide our analysis of the scientific information documented in the SSA report, we have not only analyzed individual effects on the species, but we have also analyzed their potential cumulative effects. We incorporate the cumulative effects into our SSA analysis when we characterize the current and future condition of the species. To assess the current and future condition of the species, we undertake an iterative analysis that encompasses and incorporates the threats individually and then accumulates and evaluates the effects of all the factors that may be influencing the species, including threats and conservation efforts. Because the SSA framework considers not just the presence of the factors, but to what degree they collectively influence risk to the entire species, our assessment integrates the cumulative effects of the factors and replaces a standalone cumulative effects analysis.
Determination of Prostrate Milkweed Status
Section 4 of the Act (16 U.S.C. 1533) and its implementing regulations (50 CFR part 424) set forth the procedures for determining whether a species meets the definition of an endangered species or a threatened species. The Act defines endangered species as a species “in danger of extinction throughout all or a significant portion of its range,” and threatened species as a species “likely to become an endangered species within the foreseeable future throughout all or a significant portion of its range.” The Act requires that we determine whether a species meets the definition of endangered species or threatened species because of any of the following factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) Overutilization for commercial, recreational, scientific, or educational purposes; (C) Disease or predation; (D) The inadequacy of existing regulatory mechanisms; or (E) Other natural or manmade factors affecting its continued existence
or threatened species because of any of the following factors: (A) The present or threatened destruction, modification, or curtailment of its habitat or range; (B) Overutilization for commercial, recreational, scientific, or educational purposes; (C) Disease or predation; (D) The inadequacy of existing regulatory mechanisms; or (E) Other natural or manmade factors affecting its continued existence.
Status Throughout All of Its Range
After evaluating threats to the species and assessing the cumulative effect of
All the aforementioned threats are currently affecting the known populations of prostrate milkweed. Buffelgrass has already negatively impacted all of the Texas populations (TXNDD 2019-2020, entire; Eason 2019, pers. comm.; Kieschnick 2019, pers. comm.; Santore 2019, unpaginated) and will continue to do so in the future. Habitat loss and degradation from root-plowing and conversion of native vegetation to improved buffelgrass pasture has also already been occurring for many years (Service 2020, p. 40). Habitat loss from ROW construction and maintenance from energy development and road and utility construction has already been observed from oil and gas development occurring in Zapata County. As of November 2019, no wind turbines, oil or gas well pads, pipelines, or energy service roads have been constructed directly within known prostrate milkweed populations. However, some Starr County prostrate milkweed populations are less than 2.0 km (1.2 mi) from existing wind turbines (Service 2020, pp. 42-43), and a few wind energy farms are expected to be constructed in the future, which could lead to additional habitat loss. Habitat loss from border security development and enforcement activities has occurred in recent years and is expected to continue into the future. And, finally, the demographic and genetic consequences of small population sizes is a current threat to the prostrate milkweed. This situation is not expected to change into the future
structed in the future, which could lead to additional habitat loss. Habitat loss from border security development and enforcement activities has occurred in recent years and is expected to continue into the future. And, finally, the demographic and genetic consequences of small population sizes is a current threat to the prostrate milkweed. This situation is not expected to change into the future.
In addition to the current threats, redundancy and representation are also limited. There are twenty-four known populations that are distributed widely across its range, and the majority of those populations are currently in low condition. Should a catastrophic event occur, the populations are vulnerable to extirpation because they are small and isolated from each other. The small, reproductively isolated populations are also susceptible to the loss of genetic diversity, genetic drift, and inbreeding due to random fluctuations in recruitment (demographic stochasticity) or variations in rainfall or other environmental factors (environmental stochasticity). Because of the overall species' current resiliency, redundancy, and representation, prostrate milkweed is currently in danger of extinction throughout all of its range. We do not find the species meets the definition of a threatened species because the species has already shown low levels in current resiliency, redundancy, and representation due to the threats mentioned above. Thus, after assessing the best available information, we determine that prostrate milkweed is in danger of extinction throughout all of its range.
Status Throughout a Significant Portion of Its Range
Under the Act and our implementing regulations, a species may warrant listing if it is in danger of extinction or likely to become so in the foreseeable future throughout all or a significant portion of its range
ssing the best available information, we determine that prostrate milkweed is in danger of extinction throughout all of its range.
Status Throughout a Significant Portion of Its Range
Under the Act and our implementing regulations, a species may warrant listing if it is in danger of extinction or likely to become so in the foreseeable future throughout all or a significant portion of its range. We have determined that the prostrate milkweed is in danger of extinction throughout all of its range and accordingly did not undertake an analysis of any significant portion of its range. Because the prostrate milkweed warrants listing as endangered throughout all of its range, our determination is consistent with the decision in Center for Biological Diversity v. Everson , 2020 WL 437289 (D.D.C. Jan. 28, 2020), in which the court vacated the aspect of the Final Policy on Interpretation of the Phrase “Significant Portion of Its Range” in the Endangered Species Act's Definitions of “Endangered Species” and “Threatened Species” (79 FR 37578; July 1, 2014) that provided the Service does not undertake an analysis of significant portions of a species' range if the species warrants listing as threatened throughout all of its range.
Determination of Status
Our review of the best available scientific and commercial information indicates that the prostrate milkweed meets the definition of an endangered species. Therefore, we propose to list the prostrate milkweed as an endangered species in accordance with sections 3(20) and 4(a)(1) of the Act.
Available Conservation Measures
Conservation measures provided to species listed as endangered or threatened species under the Act include recognition, recovery actions, requirements for Federal protection, and prohibitions against certain practices. Recognition through listing results in public awareness, and conservation by Federal, State, Tribal, and local agencies, private organizations, and individuals
nservation Measures
Conservation measures provided to species listed as endangered or threatened species under the Act include recognition, recovery actions, requirements for Federal protection, and prohibitions against certain practices. Recognition through listing results in public awareness, and conservation by Federal, State, Tribal, and local agencies, private organizations, and individuals. The Act encourages cooperation with the States and other countries and calls for recovery actions to be carried out for listed species. The protection required by Federal agencies and the prohibitions against certain activities are discussed, in part, below.
The primary purpose of the Act is the conservation of endangered and threatened species and the ecosystems upon which they depend. The ultimate goal of such conservation efforts is the recovery of these listed species, so that they no longer need the protective measures of the Act. Section 4(f) of the Act calls for the Service to develop and implement recovery plans for the conservation of endangered and threatened species. The recovery planning process involves the identification of actions that are necessary to halt or reverse the species' decline by addressing the threats to its survival and recovery. The goal of this process is to restore listed species to a point where they are secure, self-sustaining, and functioning components of their ecosystems.
Recovery planning consists of preparing draft and final recovery plans, beginning with the development of a recovery outline and making it available to the public within 30 days of a final listing determination. The recovery outline guides the immediate implementation of urgent recovery actions and describes the process to be used to develop a recovery plan. Revisions of the plan may be done to address continuing or new threats to the species, as new substantive information becomes available
opment of a recovery outline and making it available to the public within 30 days of a final listing determination. The recovery outline guides the immediate implementation of urgent recovery actions and describes the process to be used to develop a recovery plan. Revisions of the plan may be done to address continuing or new threats to the species, as new substantive information becomes available. The recovery plan also identifies recovery criteria for review of when a species may be ready for reclassification from endangered to threatened (“downlisting”) or removal from protected status (“delisting”), and methods for monitoring recovery progress. Recovery plans also establish a framework for agencies to coordinate their recovery efforts and provide estimates of the cost of implementing recovery tasks. Recovery teams (composed of species experts, Federal and State agencies, nongovernmental organizations, and stakeholders) are often established to develop recovery https://www.fws.gov/endangered ), or from our Texas Coastal Ecological Services Field Office (see FOR FURTHER INFORMATION CONTACT ).
Implementation of recovery actions generally requires the participation of a broad range of partners, including other Federal agencies, States, Tribes, nongovernmental organizations, businesses, and private landowners. Examples of recovery actions include habitat restoration ( e.g., restoration of native vegetation), research, captive propagation and reintroduction, and outreach and education. The recovery of many listed species cannot be accomplished solely on Federal lands because their range may occur primarily or solely on non-Federal lands. To achieve recovery of these species requires cooperative conservation efforts on private, State, and Tribal lands.
If this species is listed, funding for recovery actions will be available from a variety of sources, including Federal budgets, State programs, and cost-share grants for non-Federal landowners, the academic community, and nongovernmental organizations
r solely on non-Federal lands. To achieve recovery of these species requires cooperative conservation efforts on private, State, and Tribal lands.
If this species is listed, funding for recovery actions will be available from a variety of sources, including Federal budgets, State programs, and cost-share grants for non-Federal landowners, the academic community, and nongovernmental organizations. In addition, pursuant to section 6 of the Act, the State of Texas would be eligible for Federal funds to implement management actions that promote the protection or recovery of the prostrate milkweed. Information on our grant programs that are available to aid species recovery can be found at: https://www.fws.gov/grants.
Although the prostrate milkweed is only proposed for listing under the Act at this time, please let us know if you are interested in participating in recovery efforts for this species. Additionally, we invite you to submit any new information on this species whenever it becomes available and any information you may have for recovery planning purposes (see FOR FURTHER INFORMATION CONTACT ).
Section 7(a) of the Act requires Federal agencies to evaluate their actions with respect to any species that is proposed or listed as an endangered or threatened species and with respect to its critical habitat, if any is designated. Regulations implementing this interagency cooperation provision of the Act are codified at 50 CFR part 402. Section 7(a)(4) of the Act requires Federal agencies to confer with the Service on any action that is likely to jeopardize the continued existence of a species proposed for listing or result in destruction or adverse modification of proposed critical habitat. If a species is listed subsequently, section 7(a)(2) of the Act requires Federal agencies to ensure that activities they authorize, fund, or carry out are not likely to jeopardize the continued existence of the species or destroy or adversely modify its critical habitat
tinued existence of a species proposed for listing or result in destruction or adverse modification of proposed critical habitat. If a species is listed subsequently, section 7(a)(2) of the Act requires Federal agencies to ensure that activities they authorize, fund, or carry out are not likely to jeopardize the continued existence of the species or destroy or adversely modify its critical habitat. If a Federal action may affect a listed species or its critical habitat, the responsible Federal agency must enter into consultation with the Service.
Federal agency actions within the species' habitat that may require conference or consultation or both as described in the preceding paragraph include management and any other landscape-altering activities on Federal lands administered by the U.S. Fish and Wildlife Service.
The Act and its implementing regulations set forth a series of general prohibitions and exceptions that apply to endangered plants. The prohibitions of section 9(a)(2) of the Act, codified at 50 CFR 17.61, make it illegal for any person subject to the jurisdiction of the United States to: Import or export; remove and reduce to possession from areas under Federal jurisdiction; maliciously damage or destroy on any such area; remove, cut, dig up, or damage or destroy on any other area in knowing violation of any law or regulation of any State or in the course of any violation of a State criminal trespass law; deliver, receive, carry, transport, or ship in interstate or foreign commerce, by any means whatsoever and in the course of a commercial activity; or sell or offer for sale in interstate or foreign commerce an endangered plant. Certain exceptions apply to employees of the Service, the National Marine Fisheries Service, other Federal land management agencies, and State conservation agencies.
We may issue permits to carry out otherwise prohibited activities involving endangered plants under certain circumstances. Regulations governing permits are codified at 50 CFR 17.62
nterstate or foreign commerce an endangered plant. Certain exceptions apply to employees of the Service, the National Marine Fisheries Service, other Federal land management agencies, and State conservation agencies.
We may issue permits to carry out otherwise prohibited activities involving endangered plants under certain circumstances. Regulations governing permits are codified at 50 CFR 17.62. With regard to endangered plants, a permit may be issued for scientific purposes or for enhancing the propagation or survival of the species. The statute also contains certain exemptions from the prohibitions, which are found in sections 9 and 10 of the Act.
It is our policy, as published in the Federal Register on July 1, 1994 (59 FR 34272), to identify to the maximum extent practicable at the time a species is listed, those activities that would or would not constitute a violation of section 9 of the Act. The intent of this policy is to increase public awareness of the effect of a proposed listing on proposed and ongoing activities within the range of the species proposed for listing. Based on the best available information, the following actions are unlikely to result in a violation of section 9, if these activities are carried out in accordance with existing regulations and permit requirements; this list is not comprehensive:
(1) Normal agricultural and silvicultural practices, including herbicide and pesticide use, that are carried out in accordance with any existing regulations, permit and label requirements, and best management practices; and
(2) Normal residential landscaping activities on non-Federal lands; and
(3) Recreational use with minimal ground disturbance.
Based on the best available information, the following activities may potentially result in a violation of section 9 of the Act if they are not authorized in accordance with applicable law; this list is not comprehensive:
(1) Unauthorized handling, removing, trampling, or collecting of prostrate milkweed on Federal land; and
l lands; and
(3) Recreational use with minimal ground disturbance.
Based on the best available information, the following activities may potentially result in a violation of section 9 of the Act if they are not authorized in accordance with applicable law; this list is not comprehensive:
(1) Unauthorized handling, removing, trampling, or collecting of prostrate milkweed on Federal land; and
(2) Removing, cutting, digging up, or damaging or destroying prostrate milkweed in knowing violation of any law or regulation of the State of Texas or in the course of any violation of a State criminal trespass law.
II. Critical Habitat
Background
Critical habitat is defined in section 3 of the Act as:
(1) The specific areas within the geographical area occupied by the species, at the time it is listed in accordance with the Act, on which are found those physical or biological features
(a) Essential to the conservation of the species, and
(b) Which may require special management considerations or protection; and
(2) Specific areas outside the geographical area occupied by the species at the time it is listed, upon a determination that such areas are essential for the conservation of the species.
Our regulations at 50 CFR 424.02 define the geographical area occupied by the species as an area that may generally be delineated around species' occurrences, as determined by the Secretary ( i.e., range). Such areas may include those areas used throughout all or part of the species' life cycle, even if not used on a regular basis ( e.g., migratory corridors, seasonal habitats, and habitats used periodically, but not solely by vagrant individuals).
Conservation, as defined under section 3 of the Act, means to use and the use of all methods and procedures that are necessary to bring an endangered or threatened species to the point at which the measures provided pursuant to the Act are no longer necessary
on a regular basis ( e.g., migratory corridors, seasonal habitats, and habitats used periodically, but not solely by vagrant individuals).
Conservation, as defined under section 3 of the Act, means to use and the use of all methods and procedures that are necessary to bring an endangered or threatened species to the point at which the measures provided pursuant to the Act are no longer necessary. Such methods and procedures include, but are not limited to, all activities associated with scientific resources management such as research, census, law enforcement, habitat acquisition and maintenance, propagation, live trapping, and transplantation, and, in the extraordinary case where population pressures within a given ecosystem cannot be otherwise relieved, may include regulated taking.
Critical habitat receives protection under section 7 of the Act through the requirement that Federal agencies ensure, in consultation with the Service, that any action they authorize, fund, or carry out is not likely to result in the destruction or adverse modification of critical habitat. The designation of critical habitat does not affect land ownership or establish a refuge, wilderness, reserve, preserve, or other conservation area. Designation also does not allow the government or public to access private lands, nor does designation require implementation of restoration, recovery, or enhancement measures by non-Federal landowners. Where a landowner requests Federal agency funding or authorization for an action that may affect a listed species or critical habitat, the Federal agency would be required to consult with the Service under section 7(a)(2) of the Act
government or public to access private lands, nor does designation require implementation of restoration, recovery, or enhancement measures by non-Federal landowners. Where a landowner requests Federal agency funding or authorization for an action that may affect a listed species or critical habitat, the Federal agency would be required to consult with the Service under section 7(a)(2) of the Act. However, even if the Service were to conclude that the proposed activity would result in destruction or adverse modification of the critical habitat, the Federal action agency and the landowner are not required to abandon the proposed activity, or to restore or recover the species; instead, they must implement “reasonable and prudent alternatives” to avoid destruction or adverse modification of critical habitat.
Under the first prong of the Act's definition of critical habitat, areas within the geographical area occupied by the species at the time it was listed are included in a critical habitat designation if they contain physical or biological features (1) which are essential to the conservation of the species and (2) which may require special management considerations or protection. For these areas, critical habitat designations identify, to the extent known using the best scientific and commercial data available, those physical or biological features that are essential to the conservation of the species (such as space, food, cover, and protected habitat). In identifying those physical or biological features that occur in specific occupied areas, we focus on the specific features that are essential to support the life-history needs of the species, including, but not limited to, water characteristics, soil type, geological features, prey, vegetation, symbiotic species, or other features. A feature may be a single habitat characteristic or a more complex combination of habitat characteristics. Features may include habitat characteristics that support ephemeral or dynamic habitat conditions
ial to support the life-history needs of the species, including, but not limited to, water characteristics, soil type, geological features, prey, vegetation, symbiotic species, or other features. A feature may be a single habitat characteristic or a more complex combination of habitat characteristics. Features may include habitat characteristics that support ephemeral or dynamic habitat conditions. Features may also be expressed in terms relating to principles of conservation biology, such as patch size, distribution distances, and connectivity.
Under the second prong of the Act's definition of critical habitat, we can designate critical habitat in areas outside the geographical area occupied by the species at the time it is listed, upon a determination that such areas are essential for the conservation of the species. The implementing regulations at 50 CFR 424.12(b)(2) further delineate unoccupied critical habitat by setting out three specific parameters: (1) When designating critical habitat, the Secretary will first evaluate areas occupied by the species; (2) the Secretary will only consider unoccupied areas to be essential where a critical habitat designation limited to geographical areas occupied by the species would be inadequate to ensure the conservation of the species; and (3) for an unoccupied area to be considered essential, the Secretary must determine that there is a reasonable certainty both that the area will contribute to the conservation of the species and that the area contains one or more of those physical or biological features essential to the conservation of the species.
Section 4 of the Act requires that we designate critical habitat on the basis of the best scientific data available. Further, our Policy on Information Standards Under the Endangered Species Act (published in the Federal Register on July 1, 1994 (59 FR 34271)), the Information Quality Act (section 515 of the Treasury and General Government Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R
tion 4 of the Act requires that we designate critical habitat on the basis of the best scientific data available. Further, our Policy on Information Standards Under the Endangered Species Act (published in the Federal Register on July 1, 1994 (59 FR 34271)), the Information Quality Act (section 515 of the Treasury and General Government Appropriations Act for Fiscal Year 2001 (Pub. L. 106-554; H.R. 5658)), and our associated Information Quality Guidelines provide criteria, establish procedures, and provide guidance to ensure that our decisions are based on the best scientific data available. They require our biologists, to the extent consistent with the Act and with the use of the best scientific data available, to use primary and original sources of information as the basis for recommendations to designate critical habitat.
When we are determining which areas should be designated as critical habitat, our primary source of information is generally the information from the SSA report and information developed during the listing process for the species. Additional information sources may include any generalized conservation strategy, criteria, or outline that may have been developed for the species; the recovery plan for the species; articles in peer-reviewed journals; conservation plans developed by States and counties; scientific status surveys and studies; biological assessments; other unpublished materials; or experts' opinions or personal knowledge.
As the regulatory definition of “habitat” reflects (50 CFR 424.02), habitat is dynamic, and species may move from one area to another over time. We recognize that critical habitat designated at a particular point in time may not include all of the habitat areas that we may later determine are necessary for the recovery of the species. For these reasons, a critical habitat designation does not signal that habitat outside the designated area is unimportant or may not be needed for recovery of the species
e from one area to another over time. We recognize that critical habitat designated at a particular point in time may not include all of the habitat areas that we may later determine are necessary for the recovery of the species. For these reasons, a critical habitat designation does not signal that habitat outside the designated area is unimportant or may not be needed for recovery of the species. Areas that are important to the conservation of the species, both inside and outside the critical habitat designation, will continue to be subject to: (1) Conservation actions implemented under section 7(a)(1) of the Act; (2) regulatory protections afforded by the requirement in section 7(a)(2) of the Act for Federal agencies to ensure their actions are not likely to jeopardize the continued existence of any endangered or threatened species; and (3) the prohibitions found in section 9 of the Act. Federally funded or permitted projects affecting listed species outside their designated critical habitat areas may still result in jeopardy findings in some cases. These protections and conservation tools will continue to contribute to recovery of the species. 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, habitat conservation plans (HCPs), or other species conservation planning
Prudency Determination
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, the Secretary shall designate critical habitat at the time the species is determined to be an endangered or threatened species. Our regulations (50 CFR 424.12(a)(1)) state that the Secretary may, but is not required to, determine that a designation would not be prudent in the following circumstances:
menting regulations (50 CFR 424.12) require that, to the maximum extent prudent and determinable, the Secretary shall designate critical habitat at the time the species is determined to be an endangered or threatened species. Our regulations (50 CFR 424.12(a)(1)) state that the Secretary may, but is not required to, determine that a designation would not be prudent in the following circumstances:
(i) 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;
(ii) The present or threatened destruction, modification, or curtailment of a species' habitat or range is not a threat to the species, or threats to the species' habitat stem solely from causes that cannot be addressed through management actions resulting from consultations under section 7(a)(2) of the Act;
(iii) Areas within the jurisdiction of the United States provide no more than negligible conservation value, if any, for a species occurring primarily outside the jurisdiction of the United States;
(iv) No areas meet the definition of critical habitat; or
(v) The Secretary otherwise determines that designation of critical habitat would not be prudent based on the best scientific data available.
As discussed earlier in this document, there is currently no imminent threat of collection or vandalism identified under Factor B for this species, and identification and mapping of critical habitat is not expected to initiate any such threat. In our SSA and proposed listing determination for prostrate milkweed, we determined that the present or threatened destruction, modification, or curtailment of habitat or range is a threat to prostrate milkweed and that those threats in some way can be addressed by section 7(a)(2) consultation measures. We are able to identify areas that meet the definition of critical habitat where the species occurs in the United States
isting determination for prostrate milkweed, we determined that the present or threatened destruction, modification, or curtailment of habitat or range is a threat to prostrate milkweed and that those threats in some way can be addressed by section 7(a)(2) consultation measures. We are able to identify areas that meet the definition of critical habitat where the species occurs in the United States. Therefore, because none of the circumstances enumerated in our regulations at 50 CFR 424.12(a)(1) have been met and because the Secretary has not identified other circumstances for which this designation of critical habitat would not be prudent, we have determined that the designation of critical habitat is prudent for prostrate milkweed.
Critical Habitat Determinability
Having determined that designation is prudent, under section 4(a)(3) of the Act we must find whether critical habitat for the prostrate milkweed is determinable. Our regulations at 50 CFR 424.12(a)(2) state that critical habitat is not determinable when one or both of the following situations exist:
(i) Data sufficient to perform required analyses are lacking, or
(ii) The biological needs of the species are not sufficiently well known to identify any area that meets the definition of “critical habitat.”
When critical habitat is not determinable, the Act allows the Service an additional year to publish a critical habitat designation (16 U.S.C. 1533(b)(6)(C)(ii)).
We reviewed the available information pertaining to the biological needs of the species and habitat characteristics where this species is located. This and other information represent the best scientific data available and led us to conclude that the designation of critical habitat is determinable for the prostrate milkweed
to publish a critical habitat designation (16 U.S.C. 1533(b)(6)(C)(ii)).
We reviewed the available information pertaining to the biological needs of the species and habitat characteristics where this species is located. This and other information represent the best scientific data available and led us to conclude that the designation of critical habitat is determinable for the prostrate milkweed.
Physical or Biological Features Essential to the Conservation of the Species
In accordance with section 3(5)(A)(i) of the Act and regulations at 50 CFR 424.12(b), in determining which areas we will designate as critical habitat from within the geographical area occupied by the species at the time of listing, we consider the physical or biological features (PBFs) that are essential to the conservation of the species and that may require special management considerations or protection. The regulations at 50 CFR 424.02 define “physical or biological features essential to the conservation of the species” as the features that occur in specific areas and that are essential to support the life-history needs of the species, including, but not limited to, water characteristics, soil type, geological features, sites, prey, vegetation, symbiotic species, or other features. A feature may be a single habitat characteristic or a more complex combination of habitat characteristics. Features may include habitat characteristics that support ephemeral or dynamic habitat conditions. Features may also be expressed in terms relating to principles of conservation biology, such as patch size, distribution distances, and connectivity. For example, physical features essential to the conservation of the species might include gravel of a particular size required for spawning, alkaline soil for seed germination, protective cover for migration, or susceptibility to flooding or fire that maintains necessary early-successional habitat characteristics
f conservation biology, such as patch size, distribution distances, and connectivity. For example, physical features essential to the conservation of the species might include gravel of a particular size required for spawning, alkaline soil for seed germination, protective cover for migration, or susceptibility to flooding or fire that maintains necessary early-successional habitat characteristics. Biological features might include prey species, forage grasses, specific kinds or ages of trees for roosting or nesting, symbiotic fungi, or a particular level of nonnative species consistent with conservation needs of the listed species. The features may also be combinations of habitat characteristics and may encompass the relationship between characteristics or the necessary amount of a characteristic essential to support the life history of the species.
In considering whether features are essential to the conservation of the species, we may consider an appropriate quality, quantity, and spatial and temporal arrangement of habitat characteristics in the context of the life-history needs, condition, and status of the species. These characteristics 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, or rearing (or development) of offspring; and habitats that are protected from disturbance.
Geological Substrate and Soils
Prostrate milkweed grows in well-drained sandy soils of the Tamaulipan shrubland region of south Texas and northeast Mexico (Service 2020, pp. 22-26). In Starr and Zapata Counties, Texas, the soils of documented sites overlie Eocene and Oligocene sandstones and clays of the Laredo, Yegua, and Jackson geological formations (Stoeser et al. 2005)
d from disturbance.
Geological Substrate and Soils
Prostrate milkweed grows in well-drained sandy soils of the Tamaulipan shrubland region of south Texas and northeast Mexico (Service 2020, pp. 22-26). In Starr and Zapata Counties, Texas, the soils of documented sites overlie Eocene and Oligocene sandstones and clays of the Laredo, Yegua, and Jackson geological formations (Stoeser et al. 2005). In some occupied sites, a stratum of indurated caliche may also be present; in south Texas, caliche refers to soil strata of precipitated calcium carbonate formed during the early Pliocene (Spearing 1998, pp. 258, 398; Baskin and Hulbert, Jr. 2008, p. 93). Soil types of these occupied sites include deep eolian Hebbronville sands, Copita fine sandy loam, Brennan fine sandy loam, eroded Maverick soils, Catarina clay, and Zapata soils (USDA 1972; USDA 2011). Elevated levels of gypsum are present at some sites.
The climate of the Tamaulipan shrubland region is subtropical and semi-arid. Much of the region's precipitation occurs during infrequent periods of heavy rainfall that interrupt prolonged spells of very hot, dry weather. Rainfall readily infiltrates into the well-drained sandy soils of prostrate milkweed habitats, but moisture does
Prostrate milkweed forms tubers underground that are able to persist in a dormant condition for one to several years. The species responds very quickly to rainfall; the tubers sprout new stems that emerge, flower, and set seed in a matter of weeks, and the plants store carbohydrates, minerals, and water in tubers. Then the above-ground portions die back during hot, dry weather. Prostrate milkweed does not occur in areas of higher rainfall or where moisture persists longer in deeper silty or clayey soils. The species does not persist when occupied sites develop a dense shrub overstory or dense cover of grasses
d set seed in a matter of weeks, and the plants store carbohydrates, minerals, and water in tubers. Then the above-ground portions die back during hot, dry weather. Prostrate milkweed does not occur in areas of higher rainfall or where moisture persists longer in deeper silty or clayey soils. The species does not persist when occupied sites develop a dense shrub overstory or dense cover of grasses. We conclude that prostrate milkweed is endemic to sites where it escapes competition from other plants through its unique adaptation to ephemeral soil moisture, prolonged drought, and tolerance of high gypsum concentrations.
Therefore, well-drained sandy soil overlying sandstone or indurated caliche strata is an essential physical feature of prostrate milkweed critical habitats. A high soil gypsum concentration contributes to the habitat suitability of some sites by reducing competition, and is an essential physical feature.
Ecological Community
Within the Tamaulipan shrubland ecological region, prostrate milkweed inhabits arid subtropical grasslands and shrub savannas. It requires an open canopy, where there is little or no shade from trees and shrubs, and relatively little competition from grasses and herbaceous plants; the estimated combined cover of woody plants, grasses, and herbaceous plants at a site in Zapata County was less than 30 percent (Damude and Poole 1990, p. 16). It is likely that naturally occurring wildfires, in the past, maintained the relatively open structure of these plant communities (Scifres and Hamilton 1993, pp. 8-21). We have observed an increased abundance of other Texas species of Asclepias, including antelope horns ( A. asperula ), Emory's milkweed ( A. emoryi ), zizotes milkweed ( A. oenotheroides ), and wand milkweed ( A. viridiflora ), during the first few years after sites have burned; this fire-following effect has been described for green milkweed ( A. viridis ) (Baum and Sharber 2012, entire)
. 8-21). We have observed an increased abundance of other Texas species of Asclepias, including antelope horns ( A. asperula ), Emory's milkweed ( A. emoryi ), zizotes milkweed ( A. oenotheroides ), and wand milkweed ( A. viridiflora ), during the first few years after sites have burned; this fire-following effect has been described for green milkweed ( A. viridis ) (Baum and Sharber 2012, entire). Prostrate milkweed, like other milkweeds, may also be stimulated to grow and flower after wildfires have reduced competition.
Most Asclepias species require outcrossing for effective fertilization of flowers. All Asclepias species have highly specialized pollination mechanisms that require animal pollinators to carry pollen from one individual to another. Although the effective pollinators of prostrate milkweed have not been determined, these are likely to include large bees and wasps. For example, the closely related zizotes milkweed is effectively pollinated by very large wasps called tarantula hawks ( Pepsis spp. and Hemipepsis spp.) (Service 2020, pp. 17, 35-36). Therefore, prostrate milkweed habitats must also support populations of large bees and wasps that, in turn, require abundant, diverse sources of pollen and nectar. Much like milkweeds, many pollen and nectar plants are fire followers that are most abundant in sites that burn periodically, but decline when fires are infrequent.
Buffelgrass is an African grass that is widely planted in south Texas for livestock forage. Buffelgrass is highly invasive, and frequently displaces native grasses and herbaceous plants (Best 2009, pp. 310-311), including prostrate milkweed (Service 2020, pp. 39-40) and the pollen and nectar plants needed to support pollinator populations. The majority of prostrate milkweed plants have been observed in disturbed soils where buffelgrass is absent or at low densities (Eason 2019, pers. comm.; Strong 2019, pers. comm.)
e, and frequently displaces native grasses and herbaceous plants (Best 2009, pp. 310-311), including prostrate milkweed (Service 2020, pp. 39-40) and the pollen and nectar plants needed to support pollinator populations. The majority of prostrate milkweed plants have been observed in disturbed soils where buffelgrass is absent or at low densities (Eason 2019, pers. comm.; Strong 2019, pers. comm.). Prostrate milkweed requires an open canopy with less than 30 percent cover of native and nonnative grasses and herbaceous plants combined (Damude and Poole 1990, p. 16); so, assuming nonnative buffelgrass is more prevalent, we estimate that 20 percent or less cover of buffelgrass is at a low enough density for prostrate milkweed to survive. Therefore, prostrated milkweed habitats must also have less than 20 percent cover of buffelgrass for prostrate milkweed to have access to sufficient resources such as sunlight.
In summary, the essential biological features of prostrate milkweed critical habitats are: (1) Open savannas and grasslands of the Tamaulipan shrubland ecological region; (2) vegetation composition that includes abundant, diverse pollen and nectar plants and healthy populations of native bee and wasp species; and (3) less than 20 percent cover of buffelgrass. Periodic prescribed burning may be necessary to maintain the open structure and diverse composition of the species' habitats.
Summary of Essential Physical or Biological Features
Additional information can be found in the SSA report (Service 2020, available on https://www.regulations.gov under Docket No. FWS-R2-ES-2021-0041). We have determined that the following physical or biological features are essential to the conservation of prostrate milkweed:
(1) Well-drained sandy soil overlying strata of sandstone or indurated caliche;
(2) High soil gypsum concentration;
(3) Open savannas and grasslands of the Tamaulipan shrubland ecological region;
on https://www.regulations.gov under Docket No. FWS-R2-ES-2021-0041). We have determined that the following physical or biological features are essential to the conservation of prostrate milkweed:
(1) Well-drained sandy soil overlying strata of sandstone or indurated caliche;
(2) High soil gypsum concentration;
(3) Open savannas and grasslands of the Tamaulipan shrubland ecological region;
(4) Vegetation composition that includes abundant, diverse pollen and nectar plants and healthy populations of native bee and wasp species; and
(5) Less than 20 percent cover of buffelgrass.
Special Management Considerations or Protection
When designating critical habitat, we assess whether the specific areas within the geographical area occupied by the species at the time of listing contain features that are essential to the conservation of the species and which may require special management considerations or protection. The features essential to the conservation of this species may require special management considerations or protection to reduce the following threats: Nonnative invasive grass; root-plowing and conversion of native vegetation to buffelgrass pasture; ROW construction and maintenance from energy development and road and utility construction; border security development and law enforcement activities; and small population sizes. Management activities that could ameliorate these threats include, but are not limited to: Prescribed burning, grazing, and/or brush thinning; nonnative invasive grass control; protection from activities that disturb the soil; and propagation and reintroduction of plants in restorable areas.
In summary, we find that the occupied areas we are proposing to designate as critical habitat contain the PBFs that are essential to the conservation of the species and that may require special management considerations or protection
rush thinning; nonnative invasive grass control; protection from activities that disturb the soil; and propagation and reintroduction of plants in restorable areas.
In summary, we find that the occupied areas we are proposing to designate as critical habitat contain the PBFs that are essential to the conservation of the species and that may require special management considerations or protection. Special management considerations or protection may be required of the Federal action agency to eliminate, or to
Criteria Used To Identify Critical Habitat
As required by section 4(b)(2) of the Act, we use the best scientific data available to designate critical habitat. In accordance with the Act and our implementing regulations at 50 CFR 424.12(b), we review available information pertaining to the habitat requirements of the species and identify specific areas within the geographical area occupied by the species at the time of listing and any specific areas outside the geographical area occupied by the species to be considered for designation as critical habitat. We are not currently proposing to designate any areas outside the geographical area occupied by the species because we have not identified any unoccupied areas that meet the definition of critical habitat. While prostrate milkweed needs additional populations to reduce the likelihood of extinction in the future, we are not able to identify additional locations that may have a reasonable certainty of contributing to conservation at this time due to limited access to privately owned lands and information regarding lands that would be good candidates for introductions in the species' range.
In summary, for areas within the geographic area occupied by the species at the time of listing, we delineated critical habitat unit boundaries using the following criteria. First, using ArcGIS software, we identified potential habitats in Starr and Zapata Counties that have the essential features of geology and soils described above
ld be good candidates for introductions in the species' range.
In summary, for areas within the geographic area occupied by the species at the time of listing, we delineated critical habitat unit boundaries using the following criteria. First, using ArcGIS software, we identified potential habitats in Starr and Zapata Counties that have the essential features of geology and soils described above. The geographic information we obtained about the known populations exists as: (1) Vegetation surveys of entire tracts of land; (2) Element Occurrence (EO) polygons represented in the TXNDD; or (3) points and lines represented in the TXNDD. We then adapted methods to delineate critical habitats for each type of geographic information.
We delineated all of the potential habitats that occur at the Arroyo Ramirez tract and the Arroyo Morteros tract of the Lower Rio Grande Valley NWR as proposed critical habitat (Units 2 and 5). The Lower Rio Grande Valley NWR comprises several disconnected land parcels, rather than one big land area, and these parcels are referred to as “tracts.” The two tracts that are included in proposed Units 2 and 5 are isolated areas of refuge land. These NWR tracts are managed for the conservation of native plants and animals, and we have conducted plant surveys and have extensive knowledge of habitat suitability of these tracts.
Similarly, we delineated all of the potential habitats that occur at a private ranch (Unit 6) that is managed for wildlife and plant conservation as proposed critical habitat. The landowner has granted access for plant surveys and vegetation studies to researchers from the Texas Parks and Wildlife Department, academic institutions, and the Service. Two of the known populations are represented as polygons in the TXNDD located in the ROWs of unpaved county roads in Starr County. We have no information about the land uses or habitat suitability of areas outside these polygons
landowner has granted access for plant surveys and vegetation studies to researchers from the Texas Parks and Wildlife Department, academic institutions, and the Service. Two of the known populations are represented as polygons in the TXNDD located in the ROWs of unpaved county roads in Starr County. We have no information about the land uses or habitat suitability of areas outside these polygons. We delineated all of the potential habitats that occur within these polygons (Units 4 and 7) as proposed critical habitat. Three of the known populations are represented as one or more points or lines in the TXNDD located on privately owned land. We have no information about the land uses or habitat suitability of areas outside the points and lines. Because critical habitats must be areas, not points or lines, we delineated all areas of potential habitat within a buffer of 50 m (164 ft) from these points and lines as proposed critical habitat units; we chose the 50-m distance because the TXNDD also used a 50-m buffer for most of these features to account for estimated geographic precision. To complete the delineations of critical habitat areas, we overlaid each critical habitat area described above on Digital Ortho-Quarter Quad aerial photographs to identify and exclude any portions of sites that consisted of unvegetated road beds that are frequently driven and are maintained by road grading, as well as structures and other developed areas that did not contain the geological and soil substrates and vegetative cover that are essential physical and biological features.
We did not include one historical observation that has only approximate location data and cannot be mapped. We also did not include any of the populations reported in the U.S. Highway 83 ROW, all of which have declined since they were first reported. For example, part of EO 3 (Dolores) along U.S. 83 had about 200 individuals in 1988; four surveys conducted from 2009 to 2017 found from 0 to 3 individuals
not include one historical observation that has only approximate location data and cannot be mapped. We also did not include any of the populations reported in the U.S. Highway 83 ROW, all of which have declined since they were first reported. For example, part of EO 3 (Dolores) along U.S. 83 had about 200 individuals in 1988; four surveys conducted from 2009 to 2017 found from 0 to 3 individuals. The degree and frequency of soil disturbance in the ROWs of improved highways has caused almost complete replacement of the native plant community with introduced species, such as buffelgrass. Hence, the essential physical and biological features are no longer present along this improved highway RO

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Source: Frix Law Library, https://www.frixlaw.com/law-library/statutes/FR_PRORULE_2022-02544. Check the current official text before relying on it. Not legal advice.