Species Status Assessment Report for the Chapin Mesa Milkvetch, Astragalus schmolliae Prepared by the Western Colorado Ecological Services Field Office U.S. Fish and Wildlife Service, Grand Junction, Colorado January 2018 Photo of Chapin Mesa Milkvetch taken by USFWS employee This document was prepared by Dara Taylor with assistance from other members of the Chapin Mesa milkvetch SSA Team, including Sarah Backsen (U.S. Fish and Wildlife Service). Chapin Mesa milkvetch SSA Report i January 2018 Valuable peer and partner reviewers of a draft of this document were provided by Carol Dawson (Bureau of Land Management), Jennifer Ramp Neale (Denver Botanic Gardens), Erin Riggs (Utah Valley University Herbarium), David Anderson (Colorado Natural Heritage Program), Tova Spector (Mesa Verde National Park), Renee Rondeau (Colorado Natural Heritage Program), Jill Handwerk (Colorado Natural Heritage Program), and Jessica Smith (Colorado Natural Heritage Program). Suggested reference: U.S. Fish and Wildlife Service. 2018. Species status assessment report for the Chapin Mesa milkvetch (Astragalus schmolliae). Lakewood, CO. Chapin Mesa milkvetch SSA Report ii January 2018 Executive Summary This species status assessment (SSA) reports the results of the comprehensive biological status review by the U.S. Fish and Wildlife Service (Service) for the Chapin Mesa milkvetch (Astragalus schmolliae), and provides a thorough account of the species’ overall viability and, therefore, extinction risk. Chapin Mesa milkvetch is a narrow endemic perennial herb known to occur only in the southwestern corner of Colorado on land administered by Mesa Verde National Park and Ute Mountain Ute Tribal Park. This SSA report is intended to provide the best available biological information to inform the decision on whether or not Chapin Mesa milkvetch is warranted for listing under the Endangered Species Act (Act), and if so, whether and where to propose designation of critical habitat. To evaluate the biological status of the Chapin Mesa milkvetch both currently and into the future, we assessed a range of conditions to allow us to consider the species’ resiliency, redundancy, and representation (together, the 3Rs). The Chapin Mesa milkvetch needs multiple resilient subunits distributed across its range to maintain its persistence into the future and to avoid extinction. A number of factors influence whether Chapin Mesa milkvetch subunits are considered to be resilient to stochastic events. These factors include (1) sufficient population size (density), (2) recruitment of Chapin Mesa milkvetch into the population, as evidence by the presence of all life stages at some point during the growing season, and (3) connectivity between populations. We evaluate a number of stressors that influence the health and resiliency of Chapin mesa milkvetch popuations such as: competition with nonnative invasive plant species (i.e. cheatgrass, musk thistle, etc.), wildfire, drought, fire management activities, development of infrastructure, trampling, herbivory, and climate change. This species consists of one large interconnected population, and like many endemic (native or restricted to a certain area) plants, Chapin Mesa milkvetch is globally rare, but is locally abundant throughout its occupied habitat (Rondeau 2017, p. 1). Since Chapin Mesa milkvetch is considered to consist of one large population, for the purposes of our analysis, we divided the range of Chapin Mesa milkvetch into four representative units (Chapin Mesa, West Chapin Spur, Park Mesa, and Ute Mountain Ute Tribal Park). As we consider the future viability of the species, we believe that a greater number of self-sustaining units that are distributed across the known range of the species is associated with an overall higher viability of the species. We consider units without nonnative invasive species, development of infrastructure, and with a sufficient percentage of pinyon-juniper canopy cover, an intact native understory, sufficient percentage of seedling survival, and sufficient levels of winter and spring precipitation to be the most resilient. Chapin Mesa milkvetch SSA Report iii January 2018 Future Scenarios The viability of the Chapin Mesa milkvetch depends on maintaining multiple self-sustaining subunits over time. Climate change models forecast warmer temperatures and a decrease in precipitation, or change in the timing and type of precipitation by the year 2035. Given our uncertainty regarding the future effects of climate change, as well as the other stressors, we predict resiliency, redundancy, and representation of Chapin Mesa milkvetch under three plausible future scenarios. The scenarios we evaluated are as follows (scenarios are discussed in greater detail in Chapter 4. Species Future Condition and Status: Scenario 1 “Optimistic” - continuation of the current land management conditions under a “Warm and Wet” future climate change model; Scenario 2 “Moderate” - slight increase in fire management actives (i.e. fuels reduction activities) and infrastructure development under a “Moderately Hot” future climate change model; Scenario 3 “Pessimistic” - significant increase in fire management activities and infrastructure development under a “Hot and Dry” future climate change model. We evaluate each of these scenarios in terms of how it would be expected to impact resiliency, redundancy, and representation of the species by the year 2035. Summary We anticipate that the largest Chapin Mesa milkvetch representative unit, Chapin Mesa, will continue to be occupied under all three scenarios, but with reduced levels of resiliency. Under Scenario 3 we do anticipate that there will be a reduction in resiliency, redundancy, and representation; which may put the species at an increased risk of stochastic and catastrophic events, such that the smaller representative units may no longer be occupied by Chapin Mesa milkvetch. However, this species inherently has, and has likely always had, a low level of redundancy and representation due to its narrow endemism. Because there is only one large representative unit and three very small units; this species is already at some risk of catastrophic events and may have low adaptability to changing conditions. Chapin Mesa milkvetch SSA Report iv January 2018 Table of Contents Executive Summary ....................................................................................................................... iii Table of Contents ............................................................................................................................ v List of Figures and Tables.............................................................................................................. iii Chapter 1: Introduction ................................................................................................................... 1 Chapter 2- Species Ecological Needs ............................................................................................. 3 2.1 Biology and Life History....................................................................................................... 3 2.1.2. Historical and Current Range and Distribution ............................................................. 4 2.1.3. Life History.................................................................................................................... 7 2.2. Habitat .............................................................................................................................. 8 2.3. Individual Needs ............................................................................................................... 8 2.4. Population Needs ............................................................................................................ 12 2.5 Species Needs .................................................................................................................. 13 Chapter 3. Current Condition ........................................................................................................ 14 3.1 Stressors Affecting Chapin Mesa milkvetch and Habitat ................................................... 14 3.2 Metrics for Evaluating Current Condition .......................................................................... 24 3.3 Description of Current Conditions ...................................................................................... 28 3.4 Current Condition - Resiliency, Redundancy, and Representation ..................................... 33 Chapter 4. Species Future Condition and Status ........................................................................... 35 4.1 Characterization of Species’ Resiliency, Redundancy, and Representation by Future Scenarios ................................................................................................................................... 38 Scenario 1 – Optimistic Scenario .......................................................................................... 38 Scenario 2 – Moderate Scenario ............................................................................................ 39 Scenario 3 – Pessimistic Scenario ......................................................................................... 40 4.2 Summary of Evaluation of Scenarios .................................................................................. 42 Literature Cited ............................................................................................................................. 42 Appendix