Species Status Assessment Report for Pediomelum Pentaphyllum (Chihuahua Scurfpea)
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Species Status Assessment Report for Pediomelum pentaphyllum (Chihuahua Scurfpea) Photo: Mike Howard (Ret), Bureau of Land Management (2006) April 2018 U.S. Fish and Wildlife Service Region 2 Albuquerque, NM This document was prepared by Mark W. Horner and Angela D. Anders, Ph.D. We received valuable input and feedback from the following reviewers: George D. Dennis, Ph.D., U.S. Fish and Wildlife Service, New Mexico Ecological Services Field Office Patrick Alexander, Botanist, Bureau of Land Management, Las Cruces District Office Joneen Cockman, Ph.D., Botanist, Bureau of Land Management, Safford Field Office Sabra Tonn and Sue Schuetze, Arizona Heritage Data Management System, Arizona Game and Fish Department Julie Crawford, Ph.D., Plant Ecologist, U.S. Fish and Wildlife Service, Arizona Ecological Services Field Office We greatly appreciate their comments, which resulted in a more robust status assessment and report. We would also like to thank Chris Best, U.S. Fish and Wildlife Service, Texas Ecological Services Field Office for his help in researching the Mexican herbaria and databases. Suggested reference: U.S. Fish and Wildlife Service. 2018. Species status assessment report for Pediomelum pentaphyllum (Chihuahua scurfpea). New Mexico Ecological Services Field Office, Version 1.0. Albuquerque, NM. Pediomelum pentaphyllum SSA ii April 2018 Species Status Assessment Report for Pediomelum pentaphyllum (Chihuahua Scurfpea) Prepared by the U.S. Fish and Wildlife Service EXECUTIVE SUMMARY This Species Status Assessment (SSA) presents the results of a status review for Pediomelum pentaphyllum (Chihuahua scurfpea). It provides an assessment of the species’ needs, its current status, stressors, and future viability. For the purposes of this assessment, we define viability as the capacity to maintain populations in natural ecosystems over time. The SSA framework uses the conservation biology principles of resiliency, redundancy, and representation (collectively known as the 3-Rs) as a lens to evaluate the current and future condition of the species. The first tenet of the 3Rs is resiliency. Resilient populations are those that are able to withstand stochastic events and can generally be measured through metrics of population health. Highly resilient populations are better able to withstand disturbances such as random fluctuations in birth rates (i.e., demographic stochasticity), variations in precipitation (i.e., environmental stochasticity), or the effects of anthropogenic activities. Second is redundancy, which describes the ability of a species to withstand catastrophic events that may adversely impact one or more population. Redundancy can be measured by the number of populations, their resiliency, and their distribution and overall connectivity across the landscape. Lastly is representation. This component describes the ability to adapt to changing environmental conditions and can be measured by the breadth of genetic or habitat diversity within and among populations. Pediomelum pentaphyllum is a desert perennial with a sizable taproot/tuber that can facilitate survival through drought conditions. The species occurs in areas of deep, sandy soils in shrublands or marginal grasslands of the Chihuahuan Desert floristic region. Flowering occurs from March through May and, given favorable monsoon precipitation, again from July through September. In dry years, P. pentaphyllum can remain dormant with no aboveground growth and it is thought that dormancy can last for up to three growing seasons (spring-monsoon-spring) without plant mortality. The species occurred historically in New Mexico, Arizona, and Chihuahua, Mexico and may have also occurred in west Texas. It is currently known from four discrete, geographically defined analysis units located in southwestern New Mexico and southeastern Arizona (Figure ES-1). There remains, however, a significant amount of unsurveyed potential habitat adjacent to these areas, and in Mexico. Numbers of individual plants within the analysis units are apparently increasing with survey effort. Thus, it is at least plausible that the known abundance and area of distribution of P. pentaphyllum will increase over time as additional surveys are completed. No genetic analyses of P. pentaphyllum have been conducted. This species appears to occupy a relatively Pediomelum pentaphyllum SSA iii April 2018 Figure ES-1. Habitat suitability models for Pediomelum pentaphyllum. Pediomelum pentaphyllum SSA iv April 2018 narrow habitat niche of deep, sandy soils where erosional or depositional processes tend to dominate. However, such soil types and their transitional ecotones are widespread in the Chihuahuan Desert. Our analyses of current conditions and future impacts on P. pentaphyllum long-term viability identified three factors/stressors that pose the greatest risk to the species: herbicide application for grassland restoration (reduction of woody shrub invasion), changes in precipitation associated with climate change, and surface disturbance (infrastructure installation and maintenance, oil and gas development, mining/mineral extraction, agricultural development, residential growth, wildlife herbivory, and livestock grazing). To evaluate the status of P. pentaphyllum into the future, we considered a range of possible conditions of the above stressors for the time periods of 2025-2049 and 2050-2074. We then assessed P. pentaphyllum resiliency, redundancy, and representation under five future scenarios. In addition, we constructed a deterministic habitat suitability model for two purposes: 1) as a demographic measure for the amount of potential habitat and 2) as a heuristic guide for future survey efforts. The former was used as a relative measure of the amount of perceived potential habitat where the analysis units could conceivably expand beyond their known extent. Figure ES-1 also shows the results of this model contrasted with a previous model. Under Scenario 1, Optimistic, due to appropriate protective measures on all Federal lands, we assume minimal impacts from herbicide use; no additional surface disturbance; and the least aggressive emissions scenario in which global warming is kept to 2°C (3.6°F) above pre- industrial temperatures via emissions mitigations. Under this scenario, we would expect P. pentaphyllum resiliency, redundancy, and representation to be identical to the Current Conditions. Specifically, two analysis units would be in a High resiliency condition, one would score as an overall Moderate, and one would be in a Low/Moderate condition (Table ES-1). Under Scenarios 2a (2025-2049) and 2b (2050-2074), Intermediate Impacts, we assume continued or increased herbicide use with continuing protective measures on all Federal lands; surface disturbance activities continued at current or slightly increased levels, and the intermediate climate change regime. Under these scenarios, we would expect P. pentaphyllum viability to be characterized by slightly lower levels of resiliency. However, overall resiliency ratings would categorically remain the same as those under Current Conditions and Scenario 1, with two analysis units in High overall condition, one in Moderate condition, and one in Low/Moderate condition (Table ES-1). Under Scenario 3a (2025-2049) and 3b (2050-2074), Increased Stressors, we assume an increase in herbicide use over previous scenarios with continuing protective measures on all Federal lands; an increase in surface disturbance activities on Federal and private lands; and climate change as characterized by an aggressive and uncompromising emissions scenario. Although resiliency scores slightly decrease relative to Scenarios 2a and 2b, the resiliency ratings would remain the same relative to Current Conditions (Table ES-1). Pediomelum pentaphyllum SSA v April 2018 Table ES-1. Pediomelum pentaphyllum analysis unit resiliency under current conditions and five possible future scenarios. Pediomelum pentaphyllum SSA vi April 2018 Table of Contents Page Executive Summary ...................................................................................................................... iii CHAPTER 1 Introduction .......................................................................................................... 1 CHAPTER 2 Biology, Ecology, and Habitat Suitability Model .............................................. 3 2.1. Taxonomy ............................................................................................................................... 3 2.2. Genetics .................................................................................................................................. 4 2.3. Morphological Description ..................................................................................................... 5 2.4. Life History, Ethnobotany, and Protection Status .................................................................. 6 2.5. Range and Distribution ......................................................................................................... 10 2.5.1. Historical and Current Range ............................................................................. 10 2.6. Resource Needs ..................................................................................................................... 16 2.6.1. Physiographic and Floristic Regions ................................................................. 16 2.6.2. Plant Community, Associated Species, and Soils .............................................. 16 2.7. Habitat Suitability