SPECIES STATUS ASSESSMENT OF GUADALUPE FESCUE (FESTUCA LIGULATA SWALLEN) VERSION 1.0 August 2016 Southwest Region U.S. Fish and Wildlife Service Albuquerque, NM Guadalupe Fescue Species Status Assessment – Aug 2016 Prepared by Chris Best, Austin Ecological Services Field Office, with assistance from Hayley Dikeman, Stacey Stanford, and Nathan Allan (U.S. Fish and Wildlife Service), Dr. Joe Sirotnak (U.S. National Park Service), and Dr. Norma Fowler (University of Texas at Austin). Suggested citation: U.S. Fish and Wildlife Service. 2016. Species status assessment of Guadalupe Fescue (Festuca ligulata Swallen), Version 1.0. U.S. Fish and Wildlife Service Southwest Region, Albuquerque, New Mexico. 52 pp. + 3 appendices. i Guadalupe Fescue Species Status Assessment – Aug 2016 EXECUTIVE SUMMARY Guadalupe fescue (Festuca ligulata) is a grass species found only in a few high mountains of the Chihuahuan Desert, in trans-Pecos Texas and Coahuila, Mexico. These “sky island” habitats are conifer-oak woodlands above 1,800 meters (5,905 feet (ft)) elevation. The species has been reported in only six sites. It was first collected in 1931 in the Guadalupe Mountains, Culberson County, Texas, and in the Chisos Mountains, Brewster County, Texas; these sites are now within Guadalupe Mountains National Park and Big Bend National Park, respectively. Guadalupe fescue was documented near Fraile, southern Coahuila, in 1941, in the Sierra la Madera, central Coahuila, in 1977, and two sites in the Maderas del Carmen mountains of northern Coahuila in 1973 and 2003. The last three sites are within Protected Natural Areas (Areas Naturales Protegidas, ANP) designated by the Mexican federal government. Data collected by Texas Parks and Wildlife Department and Big Bend National Park reveals that Guadalupe fescue is a short-lived perennial with relatively low fecundity. The monitored population at Big Bend National Park has decreased significantly over time; this may be explained by a recruitment rate that is too low to sustain the population. Since grasses are wind- pollinated, small, widely scattered populations produce few if any seeds from out-crossing (pollination by unrelated individuals); the remaining individuals are probably highly inbred. We have not calculated a minimum viable population size for the species. However, by comparison to plants with similar life histories, we estimate that at least 500 to 1,000 individuals are necessary for long-term population viability. To estimate the amount and distribution of potential Guadalupe fescue habitat, we created maps of conifer-oak forests in the Chihuahuan Desert at elevations greater than 1,800 m; since larger habitat areas may be more suitable, we restricted this model to areas greater than 200 hectares (ha) (494 acres (ac)). This model reveals that northern Mexico has 283 areas of potential habitat totaling 537,998 ha (over 1.3 million ac), compared to 20 such areas totaling 27,881 ha (68,894 ac) in Texas. Thus, about 95 percent of the potential habitat is in Mexico. Wildfires occurred in the vicinity of the Chisos population at least 10 times between 1770 and 1940; the last major fire there was more than 70 years ago, due to fire suppression within the National Park. Periodic wildfire and leaf litter reduction may be necessary for long-term survival of Guadalupe fescue populations, although this has not been investigated. The long absence of fire and the resulting accumulation of fuels also increase the risk of more intense wildfire and potential loss of the remaining Guadalupe fescue population. The Service, Big Bend National Park, and Guadalupe Mountains National Park established an updated Candidate Conservation Agreement on August 26, 2008. The objectives of this 10-year agreement include monitoring and surveys, seed and germ plasm banking, fire and invasive species management, trail management, educating staff and visitors, establishing an advisory team of species experts, and cooperation with Mexican agencies and researchers to conserve the known populations and search for new ones. Research objectives include investigations of fire ecology, habitat management, genetic structure, reproductive biology, and reintroduction. ii Guadalupe Fescue Species Status Assessment – Aug 2016 Factors that may affect the continued survival of Guadalupe fescue include the genetic and demographic consequences of small population sizes and isolation of its known populations, changes in the wildfire cycle and vegetation structure, livestock grazing, trampling from humans and pack animals, trail runoff, competition from invasive species, the effects of climate change, such as higher temperature and changes in the amount and pattern of rainfall, and fungal infection of seeds. Of six historically known populations, the species is currently known from two extant populations. The Chisos Mountains population is far smaller than our estimated minimum viable population level, and despite protection, appropriate management, and periodic monitoring by the U.S. National Park Service, it has declined between 1993 and 2014. The other extant population, at ANP Maderas del Carmen in northern Coahuila, Mexico, was probably viable as recently as 2003, and the site is managed for natural resources conservation. The population at Guadalupe Mountains National Park has not been seen in more than 60 years and is presumed extirpated. The status of three other populations, all in Coahuila, is unknown. It is possible that undiscovered populations of Guadalupe fescue exist in northern Mexico and that the overall status of the species may be better than we are currently able to determine. We assess the species’ future viability, under a range of scenarios, and conclude that viability will be influenced by the effectiveness of conservation and management of populations and habitats, public outreach and support, continued surveys to document the species’ existing populations and range, and the severity of climate changes. iii Guadalupe Fescue Species Status Assessment – Aug 2016 Table of Contents. Executive Summary ii I. Introduction. 1 II. Species Information. 3 II.1. Morphology. 3 II.2. Taxonomy. 3 II.3. Genetic Diversity. 3 II.4. Phenology and Reproduction. 4 II.5. Survival Rates, Lifespan, and Demographic Trends. 5 II.6. Habitat. 7 II.7. Geographic Range. 10 II.8. Range of Estimated Potential Habitats. 14 II.9. Ecology and the Wildfire Cycle. 19 III. Summary of Individual, Population, and Species Requirements. 20 III.1. Requirements of Individuals. 20 III.2. Requirements of Populations. 21 III.3. Species Requirements. 22 IV. Factors Affecting the Survival of Guadalupe Fescue: Threats, vulnerabilities, and 24 conservation challenges. V. Conservation Efforts. 35 VI. Current Status and Viability. 36 VI.1. Current Viability. 38 VII. Assessment of Future Viability. 41 VIII. Literature Cited. 46 IX. Photographic Credits. 52 X. Acronyms Used. 52 XI. Scientific Units. 52 Appendix A. Glossary of Scientific and Technical Terms. 53 Appendix B. Analyses of Monitoring Plot Data at Big Bend National Park, Texas. 57 Appendix C. Cause and Effects Evaluations for Guadalupe Fescue. 70 iv Guadalupe Fescue Species Status Assessment – Aug 2016 List of Tables. 1. Guadalupe fescue population data at Big Bend National Park. 6 2. Plant species associated with Guadalupe fescue. 8 3. Historic and current populations of Guadalupe fescue. 12 4. Estimates of pine, oak, and pine-oak habitats above 1,800 m in the Chihuahuan 16 Desert, Texas and northern Mexico. 5. Minimum viable population guidelines applied to Guadalupe fescue. 21 6. Means and dispersion of 30 climate models for Brewster County Climate 28 Projections: 2050 to 2074 compared to 1950 to 2005, RCP 4.5 scenario. 7. Summary of current status of Guadalupe fescue populations. 37 8. Summary of requirements, factors affecting survival, and current conditions of 39 Guadalupe fescue individuals and populations, and the species’ viability (representation, redundancy, and resilience). 9. Future viability under a range of scenarios. 45 List of Figures. 1. Species Status Assessment Framework. 1 2. Guadalupe fescue at Big Bend National Park: Population size and annual 6 precipitation. 3. Images of Guadalupe fescue. 9 4. Global distribution of Guadalupe fescue. 13 5. Guadalupe fescue habitat factors. 17 6. Potential Guadalupe fescue habitat in Texas and Mexico. 18 7. Projected changes in August maximum temperature (C°), Brewster County, Texas. 30 8. Projected changes in January minimum temperature (C°), Brewster County, Texas. 31 9. Projected changes in annual precipitation (mm/day), Brewster County, Texas. 32 10. Projected changes in annual evaporative deficit (mm/month), Brewster County, 33 Texas. v Guadalupe Fescue Species Status Assessment – Aug 2016 I. Introduction. Guadalupe fescue (Festuca ligulata) is a grass species found only in a few high mountains of the Chihuahuan desert, in Trans-Pecos Texas and Coahuila, Mexico. The Trans-Pecos is the region of Texas west of the Pecos River, and Coahuila is a state in northern Mexico (see Figure 4 below). Guadalupe fescue has been a candidate for listing since 1980 (45 FR 82519). We are now reviewing the species for listing under the Endangered Species Act (Act). This Species Status Assessment (SSA) is a comprehensive status review of Guadalupe fescue to inform the listing decision and to guide future conservation efforts. This SSA will also provide the background information to guide future actions and documents, which may include listing rules, recovery plans,