Ecology, Biodiversity, Management, and Restoration of Aspen in the Sierra Nevada

Ecology, Biodiversity, Management, and Restoration United States Department of Agriculture of Aspen in the Sierra Nevada Forest Service Rocky Mountain Research Station General Technical Wayne D. Shepperd Report RMRS-GTR-178 Paul C. Rogers September 2006 David Burton Dale L. Bartos Shepperd, Wayne D.; Rogers, Paul C.; Burton, David; Bartos, Dale L. 2006. Ecology, biodiversity, management, and restoration of aspen in the Sierra Nevada. Gen. Tech. Rep. RMRS-GTR-178. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station 122 p. Abstract—This report was commissioned by the USDA Forest Service Lake Tahoe Basin Manage- ment Unit to synthesize existing information on the ecology and management of aspen (Populus tremuloides) in the Sierra Nevada of California and surrounding environs. It summarizes available information on aspen throughout North America from published literature, internal government agency reports, and experienced scientists and managers. The historic distribution, abundance, and ecologic role of aspen in the Sierra Nevada are discussed, along with the reproductive physiology of aspen. Issues that affect aspen health and vigor in the Sierra Nevada and elsewhere are covered, along with methodology for assessing the condition of aspen and monitoring the effects of management activities to restore and maintain aspen. Descriptions of the types of aspen that occur in the Sierra Nevada are presented along with alternative techniques to manage and restore aspen that are applicable wherever aspen is found. Key words: aspen, Populus tremuloides, ecology, management, disturbance, Sierra Nevada, Lake Tahoe basin, monitoring, and assessment The Authors Wayne D. Shepperd is a Research Silviculturist at the USDA Forest Service Rocky Mountain Research Station in Ft. Collins, CO. He holds a B.S. in Outdoor Recreation and M.S. and Ph.D. degrees in Silviculture from Colorado State University. He is a recognized authority on aspen and has published numerous scientific papers on aspen ecology and management during his 37 year career with the U.S. Forest Service. Paul C. Rogers is a Forest Ecology doctoral candidate at Utah State University in Logan, Utah. He previously worked as an analyst for the Forest Health Monitoring and Forest Inventory and Analysis programs in the Rocky Mountain Research Station. Paul holds a B.S. in Geography from Utah State University and an M.S. in Geography from the University of Wisconsin-Madison. His research interests include biogeography, aspen, lichenology, forest monitoring, and disturbance ecology. David Burton, a full time Bureau of Land Management and United States Forest Service volunteer and recipient of the Chief’s Forest Service Individual Volunteer Award for 2002, is principal co- ordinator of the Aspen Delineation Project, a collaborative effort of the Pacific Southwest Region (R5), California State Office-BLM, and California Department of Fish and Game. The project fo- cuses on how agencies have identified, mapped, treated, monitored, and studied aspen habitats. It also explores challenges, issues, and roadblocks surrounding aspen management. Dale L. Bartos is a Research Ecologist and Project Leader with the Rocky Mountain Research Station, and an Adjunct Assistant Professor at the Department of Wildland Resources, Utah State University, Logan, Utah. Rocky Mountain Research Station Natural Resources Research Center 2150 Centre Avenue, Building A Fort Collins, CO 80526 Ecology, Biodiversity, Management, and Restoration of Aspen in the Sierra Nevada Wayne D. Shepperd Paul C. Rogers David Burton Dale L. Bartos United States Department of Agriculture Forest Service Rocky Mountain Research Station Preface This publication was undertaken through a cooperative work agreement between the USDA Forest Service Lake Tahoe Basin Management Unit. Printing costs were covered by the USDA Forest Service Pacific Southwest Region. We thank them for their generous support. Much of the information contained in this publication appeared in an internal report submitted to the Lake Tahoe Basin Management Unit in January, 2006. It has since been subjected to additional peer and policy review and has been revised to include additional sources of information and clarify statements made in the earlier report. The purpose of this effort is to assemble the best information available about the ecology, biodiversity, and management of aspen (Populus tremuloides) within the Sierra Nevada ecosystem and nearby environs. However, we feel that much of the information contained in this document is applicable outside the Sierra Nevada proper and will be useful to managers elsewhere. To meet our goal, we scoured published literature, internal agency reports, and captured local expertise through personal contacts with the intent of finding the best and most pertinent information available about aspen. Because aspen is a minor component of landscapes in the Sierra Nevada, the body of published literature is somewhat limited. Therefore, we have interpreted results of research published elsewhere in North America and extrapolated that knowledge to the biophysical setting of the Sierra Nevada within the limits of our accumulated experience and knowledge of aspen ecology. In all instances, we have endeavored to separate fact from opinion, and knowledge from assumption. We feel that what we have presented here is the state of the art of what is currently known about aspen, but remind readers that local knowledge and experience gained from trial and observation through an adaptive approach to management is as valuable as anything we have included in this document. Acknowledgments We would like to thank the many people who contributed their expertise to this General Tech- nical Report. Particular thanks are due to Bobette Jones, Ecologist, Eagle Lake RD, Lassen NF; Coye Robbins, Wildlife Biologist, Almanor RD, Lassen NF; Paul Schmidt, Wildlife Biologist, Alturas Field Of- fice, BLM; Victor Lyon, Wildlife Biologist, LTBMU; and Beth Brenneman, Ecologist, LTBMU who provided us with important aspen assessment data. We would also like to acknowledge the contributions of George Gruell, Carson City, Nevada; David Goin, Reno, Nevada; and Tom Rickman, Wildlife Biologist, Eagle Lake RD, Lassen NF for their repeat photography sets that helped capture some extensive changes that have occurred to aspen habitats in California. We are very grateful for the work of Bruce Davidson, GIS Specialist, LTBMU, Jessica Iles, Wild- life Biologist, Pacific RD, Eldorado NF for their many hours in designing and revising the maps that are found in this General Technical Report, and Kay Glowes, Penryn CA, for her countless hours of editing early drafts of this document. Finally, we would like to thank Ken Tate, Rangeland Watershed Specialist, UC Davis; Walt Mueg- gler, Rocky Mountain Research Station (retired); Hugh Safford, Regional Ecologist, USFS, Pacific Southwest Region; Shane Romsos, Wildlife Biologist, LTBMU; Mollie Hurt, Wildlife Biologist, LTBMU; David Fournier, Vegetation Management Planer, LTBMU; and Linda Joyce, Project Leader, RMRS for their diligent review of this synthesis. iii Contents Preface ..........................................................................................................iii Acknowledgments .........................................................................................iii Chapter 1. Introduction ...............................................................................1 Chapter 2. Natural and Historical Setting ...................................................7 Physical Environment ........................................................................................7 Defining the Area of Concern ....................................................................7 Ecoregion Sections .....................................................................................7 Aspen Distribution .....................................................................................9 Geology and Glaciation ...........................................................................10 Water and Hydrology ..............................................................................12 Climate Effects on Vegetation..........................................................................14 Long-Term Climate Variability ..................................................................14 A 1000-Year Record .................................................................................14 Recent Climates and Future Directions ....................................................15 Historical Disturbance Ecology .......................................................................16 Pre-Settlement .........................................................................................17 Euro-American Settlement .......................................................................18 Modern Era ..............................................................................................20 Chapter 3. Aspen Ecology ..........................................................................23 Physiology of Aspen ........................................................................................23 Aspen’s Ecological Amplitude and Habitat ...............................................23 Clonal Habit and Root Systems ................................................................24 Damaging Agents Affecting Aspen ..................................................................26

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