U.S. FISH & WILDLIFE SERVICE Joshua Tree Species Status Assessment Felicia Sirchia, Scott Hoffmann, and Jennifer Wilkening 10/23/2018 Acknowledgements First and foremost, we would like to thank Tony Mckinney, Carlsbad Fish and Wildlife Office (CFWO) GIS Manager. Tony acquired and summarized data and generated maps for the Species Status Assessment (SSA) – information critical to development of the SSA. Thanks to our Core Team members Jennifer ‘Jena’ Lewinshon, Utah Fish and Wildlife Office, and Brian Wooldridge, Arizona Fish and Wildlife Office. Both these folks were involved early in the SSA development process and provided background on the SSA framework and constructive, helpful feedback on early drafts. Thanks to Bradd Bridges, CFWO Listing and Recovery Chief, and Jenness McBride, Palm Springs Fish and Wildlife Office Division Chief, who provided thorough, helpful comments on early drafts. Thanks to the rest of the Core Team: Arnold Roessler, Region 8, Regional listing Lead; Nancy Ferguson, CFWO; Justin Shoemaker, Region 6; Cheryll Dobson, Region 8 Solicitor; and Jane Hendron, CFWO Public Affairs. All these folks provided constructive, thoughtful comments on drafts of the SSA. Last but not least, we want to thank Wayne Nuckols, CFWO librarian, who provided invaluable research and reference support. Recommended Citation: U.S. Fish and Wildlife Service. 2018. Joshua Tree Status Assessment. Dated October 23, 2018. 113 pp. + Appendices A–C. i Table of Contents Acknowledgements ........................................................................................................................................ i 1.0 EXECUTIVE SUMMARY ...................................................................................................................... 1 2.0 INTRODUCTION ................................................................................................................................. 3 3.0 SSA METHODOLOGY ......................................................................................................................... 4 Analytical Framework ............................................................................................................................... 4 4.0 BIOLOGICAL BACKGROUND INFORMATION ........................................................................................... 5 Taxonomy .................................................................................................................................................. 5 Species Description ................................................................................................................................... 6 Range and Distribution ............................................................................................................................. 8 Contemporary Distribution ................................................................................................................... 9 Habitat .................................................................................................................................................... 12 Populations ......................................................................................................................................... 17 Life History and Demographics ............................................................................................................... 22 5.0 SPECIES NEEDS ...................................................................................................................................... 28 Individual Needs...................................................................................................................................... 28 Population Needs .................................................................................................................................... 29 Species Needs: Representation and Redundancy .................................................................................. 31 Redundancy ........................................................................................................................................ 31 Representation.................................................................................................................................... 31 6.0 SPECIES STATUS – CURRENT CONDITION ............................................................................................. 32 Uncertainties ........................................................................................................................................... 32 Stressors Potentially Affecting the Current Condition of Yucca brevifolia and Yucca jaegeriana Populations ............................................................................................................................................. 33 Yucca brevifolia ....................................................................................................................................... 33 Altered Fire Regimes and Invasive Annual Grasses ............................................................................ 33 Climate Trends .................................................................................................................................... 37 Habitat Loss ......................................................................................................................................... 41 Herbivory............................................................................................................................................. 45 ii Overutilization ..................................................................................................................................... 46 Nitrogen Enrichment (Air Pollution) ................................................................................................... 46 Yucca jaegeriana ..................................................................................................................................... 46 Altered Fire Regimes and Invasive Annual Grasses ............................................................................ 46 Climate Trends .................................................................................................................................... 49 Habitat Loss ......................................................................................................................................... 53 Herbivory............................................................................................................................................. 54 Overutilization ..................................................................................................................................... 55 Nitrogen Enrichment (Air Pollution) ................................................................................................... 55 Populations – Current Condition, Resiliency .......................................................................................... 55 Yucca brevifolia ................................................................................................................................... 57 Yucca brevifolia Current condition...................................................................................................... 60 Yucca jaegeriana ................................................................................................................................. 61 Yucca jaegeriana Current Condition ................................................................................................... 65 7.0 FUTURE CONDITION .............................................................................................................................. 66 Future Trend Assessment ....................................................................................................................... 67 Potential Stressors and Future Effects on Yucca brevifolia Populations. ............................................... 68 Altered Fire Regimes and Invasive Annual Grasses ............................................................................ 68 Climate Trends .................................................................................................................................... 71 Climate Metrics ................................................................................................................................... 73 Future Scenarios – Climate Change .................................................................................................... 77 Habitat Loss ......................................................................................................................................... 77 Military Activities ................................................................................................................................ 82 Future Scenarios – Habitat Loss .......................................................................................................... 83 Possible Synergistic Effects ................................................................................................................. 83 Summary of Potential Future Conditions on Yucca brevifolia Population Resiliency ............................. 86 YUBR South ......................................................................................................................................... 86 YUBR North ........................................................................................................................................