RECOVERY PLAN FOR TEXAS SNOWBELLS (STYRAX PLATANIFOLIUS SSP. TEXANUS) DRAFT REVISION Southwest Region U.S. Fish and Wildlife Service Albuquerque, NM April 2018 Texas Snowbells Recovery Plan, Draft Revised Disclaimer The Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et seq.), requires the development of recovery plans for listed species, unless such a plan would not promote the conservation of a particular species. Recovery plans delineate such reasonable actions as may be necessary, based upon the best scientific and commercial data available, for the conservation and survival of listed species. Plans are published by the U.S. Fish and Wildlife Service, sometimes prepared with the assistance of recovery teams, contractors, State agencies and others. Recovery plans do not necessarily represent the views, official positions or approval of any individuals or agencies involved in the plan formulation, other than the U.S. Fish and Wildlife Service. They represent the official position of the U.S. Fish and Wildlife Service only after they have been signed by the Regional Director. Recovery plans are guidance and planning documents only; identification of an action to be implemented by any public or private party does not create a legal obligation beyond existing legal requirements. Nothing in this plan should be construed as a commitment or requirement that any Federal agency obligate or pay funds in any one fiscal year in excess of appropriations made by Congress for that fiscal year in contravention of the Anti-Deficiency Act, 31 U.S.C. 1341, or any other law or regulation. Approved recovery plans are subject to modification as dictated by new information, changes in species status, and the completion of recovery actions. Please check for updates or revisions at the website below before using. Recommended Citation: U.S. Fish and Wildlife Service. 2018. Recovery plan for Texas snowbells (Styrax platanifolius ssp. texanus). Draft Revision. April, 2018. U.S. Fish and Wildlife Service, Southwest Region, Albuquerque, New Mexico. 15 pages. This recovery plan can be downloaded free of charge from the U.S. Fish and Wildlife Service website: http://ecos.fws.gov/ecp0/profile/speciesProfile?spcode=Q224 The first uses of technical terms are dash-underlined, and are defined in the glossary on pages 13-14. For convenience, the first uses of scientific units are spelled out, and are also summarized on page 12. Prepared by Chris Best, U.S. Fish and Wildlife Service, Austin Ecological Services Field Office. 2 Texas Snowbells Recovery Plan, Draft Revised I. Introduction. Texas snowbells is a rare, endemic shrub of the Edwards Plateau of Texas. On October 12, 1984, we listed Texas snowbells as an endangered species, Styrax texanus, under the Endangered Species Act of 1973, as amended (16 U.S.C. 1531 et seq; Act).) (49 FR 40036). We currently recognize this plant as S. platanifolius ssp. texanus, one of five closely related subspecies described in the most recent taxonomic treatment (Fritsch 1997). In 1987, the U.S. Fish and Wildlife Service (USFWS) finalized a recovery plan for Texas snowbells (USFWS 1987), however criteria for reclassifying the species to a threatened status (downlisting) or for removal from the endangered species list (delisting) were not established. This revised Recovery plan (Recovery Plan) takes into account the experiences and data acquired for Texas snowbells over the last three decades, and establishes criteria for downlisting and delisting. We conducted a Species Status Assessment (SSA) of Texas snowbells (USFWS 2017), which is a thorough review of the subspecies’ taxonomy, natural history, habitats, ecology, populations, and range. The SSA then analyzes individual, population, and subspecies requirements, factors affecting the subspecies’ survival, and current conditions, to assess the subspecies’ current and future viability in terms of resilience, redundancy, and representation. The SSA also includes conservation recommendations. This streamlined Recovery Plan is derived from the SSA and focuses primarily on the elements required under section 4(f)(1)(B) of the Act: (i) A description of such site-specific management actions as may be necessary to achieve the plan’s goal for the conservation and survival of the species; (ii) objective, measurable criteria which, when met, would result in a determination, in accordance with the provisions of this section, that the species be removed from the list; and (iii) estimates of the time required and the cost to carry out those measures needed to achieve the plan’s goal and to achieve intermediate steps toward that goal. In cooperation with our partners, we have also prepared a Recovery Implementation Strategy (RIS), which serves as an operational plan for stepping down the higher-level recovery actions into specific tasks (USFWS 2018b). The RIS is a separate document from this Recovery Plan and can be modified if monitoring reveals that expected results are not being achieved, therefore maximizing flexibility of recovery implementation. 3 Texas Snowbells Recovery Plan, Draft Revised II. Overview The following is a brief overview of the natural history and status of Texas snowbells. Please refer to the SSA Report (USFWS 2017) for discussion and complete literature citations. Texas snowbells (Styrax platanifolius ssp. texanus, Styracaceae) is a multi-stemmed shrub or small tree up to 6 meters (m) (20 feet [ft]) tall. The subspecies has been found only along canyons and ravines of 1st-, 2nd-, and 3rd-order streams in the upper Nueces, West Nueces, and Devils River in the Edwards Plateau of Texas (Figure 1). Naturally occurring populations have not been documented elsewhere, but could persist in the Sycamore Creek, Frio River, West Frio River, or other adjacent watersheds. The range extends 121 kilometers (km) (75 miles [mi]) east to west and 35 km (22 mi) north to south. Populations occur in limestone geological formations; annual precipitation ranges from 51.3 centimeters (cm) (20.2 inches [in]) to 69.5 cm (27.4 in); average temperatures range from a minimum of 0.9° Celsius (C) (33.6° Fahrenheit [F]) in January to a maximum of 36.3° C (97.3° F) in July; and elevations range from 372 to 579 m (1,220 to 1,900 ft). By 2013, 400 mature and 452 immature Texas snowbells plants had been documented in 22 naturally-occurring sites. Fifteen of the documented sites had fewer than 10 individuals and 2 had at least 100. Fifteen naturally occurring populations are on private land, 5 are on private conservation land (Dolan Falls Preserve and conservation easements managed by The Nature Conservancy), and 2 are on public conservation land (Devil’s River State Natural Area). The subspecies has also been reintroduced in 22 sites on private land and 2 sites at Dolan Falls Preserve. A preliminary study (Fulton 2010) found that the breeding system is obligately xenogamous (self-incompatible), and effective pollinators include the honey bee (Apis mellifera), American bumble bee (Bombus pensylvanicus), and California carpenter bee (Xylocopa californica). Sexual fertilization requires the transfer of pollen between genetically compatible individuals that are within the foraging range of suitable pollinators; effective pollination probably occurs most often between individuals that are not more than 0.5 km (0.3 mi) apart, but in rare cases pollen transfer could occur over 5 km (3.1 mi) or greater distances. Closely related individuals, such as the progeny of a single pair of plants, may not be able to fertilize each other’s flowers, and small populations may not have sufficient genetic diversity for sexual reproduction to occur. Although we do not know how many individuals are required for effective reproduction, or how widely dispersed they may be, almost all documented reproduction of Texas snowbells in the wild occurs among populations that have at least 56 mature individuals dispersed over a distance of 1.6 km (1.0 mi) or less. Mortality of seedlings and juvenile plants is high and largely due to browsing by dense populations of native white-tailed deer (Odocoileus virginianus) and introduced ungulates. Texas snowbells plants begin reproducing at about 10 years of age, and if not severely browsed, may live for many decades. A large proportion of the potential habitat of Texas snowbells is privately owned and can only be accessed with landowner permission. Much of the potential habitat on private land has probably 4 Texas Snowbells Recovery Plan, Draft Revised not been surveyed. Therefore, we believe that the actual size and numbers of populations and the degree of connectivity between them may be greater than the data from documented populations indicates. Our assessment of species viability, defined as the likelihood of persistence over the long-term, is based on the concepts of resilience, redundancy, and representation. Texas snowbells has a low level of resilience because all known populations are far below the estimated minimum viable population level. There are few populations, hence redundancy is low. The subspecies is endemic to a small area with little ecological differentiation, and has little genetic diversity and therefore has low representation. In synthesis, the viability of Texas snowbells is low. Recovery Vision. The recovery goal is the conservation and survival of Texas snowbells. Recovery will be signified by: Resilient, redundant, viable metapopulations in the Nueces, West Nueces, and Devils River watersheds (and possibly other watersheds, if other naturally-occurring populations are discovered), where spontaneous recruitment over time equals or exceeds mortality; and the conservation of its ecological and genetic representation through the restoration of gene flow throughout each extant metapopulation. Recovery Strategy. Populations are considered resilient when they are sufficiently large to endure stochastic changes. We have provisionally estimated a minimum viable population (MVP) size of 500 to 1,000 individuals. However, since suitable habitats are narrow, discontinuous patches distributed along ravines and watercourses, only a small fraction of this MVP could occur in any one place.