Management Alternatives for Natural Communities and Imperiled Butterflies at Horsetooth Mountain Park, Larimer County, Colorado
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Management Alternatives for Natural Communities and Imperiled Butterflies at Horsetooth Mountain Park, Larimer County, Colorado Steve Kettler & Phyllis Pineda Colorado Natural Heritage Program Colorado State University College of Natural Resources 254 General Services Building Ft. Collins, Colorado 80523 March, 1999 TABLE OF CONTENTS ACKNOWLEDGMENTS..........................................................................................................................III EXECUTIVE SUMMARY ........................................................................................................................ IV RECOMMENDATIONS ...................................................................................................................................... IV INTRODUCTION.........................................................................................................................................1 GOALS..............................................................................................................................................................1 NATURAL COMMUNITIES AND IMPERILED BUTTERFLIES PRESENT IN HORSETOOTH MOUNTAIN PARK ......................................................................................................................................2 BUTTERFLY DIVERSITY OF THE COLORADO FRONT RANGE .............................................................................2 MAJOR PLANT COMMUNITIES PRESENT IN HORSETOOTH MOUNTAIN PARK ....................................................3 STRESSES TO THE NATURAL COMMUNITIES AND IMPERILED BUTTERFLIES IN HORSETOOTH MOUNTAIN PARK.........................................................................................................7 ALTERED ECOLOGICAL PROCESSES..................................................................................................................7 Natural Fire Regimes .................................................................................................................................7 Natural Grazing Regimes ...........................................................................................................................8 INVASION OF NON-NATIVE SPECIES .................................................................................................................9 HABITAT LOSS, EDGE EFFECTS AND FRAGMENTATION..................................................................................12 EFFECTS OF ROADS AND TRAILS ....................................................................................................................13 MANAGING FOR NATURAL ECOLOGICAL CONDITIONS AND LANDSCAPE DIVERSITY .....................................14 MANAGEMENT TO RESTORE PLANT COMMUNITIES AND IMPERILED BUTTERFLY SPECIES ......................................................................................................................................................16 PRESCRIBED BURNING....................................................................................................................................18 GRAZING ........................................................................................................................................................19 APPLICATION OF HERBICIDES.........................................................................................................................20 BIOLOGICAL CONTROL (INSECTS)...................................................................................................................21 MOWING OR PHYSICAL REMOVAL .................................................................................................................21 PRIORITY MANAGEMENT AREAS......................................................................................................22 IMPLEMENTATION STEPS....................................................................................................................24 PRESCRIBED BURNING AND/OR GRAZING.......................................................................................................24 USE OF HERBICIDES OR PHYSICAL REMOVAL OF NON-NATIVE SPECIES ...........................................................25 THINNING OF PONDEROSA PINE WITHIN GRASSLAND AND SHRUBLAND HABITATS..........................................25 REDUCTION OF SOCIAL TRAILS .......................................................................................................................26 GENERAL .......................................................................................................................................................26 REFERENCES AND LITERATURE CITED..........................................................................................27 APPENDICES .............................................................................................................................................35 APPENDIX A - BIODIVERSITY AND THE COLORADO NATURAL HERITAGE PROGRAM.....................................36 Colorado’s Natural Heritage Program ....................................................................................................36 The Natural Heritage Network and Biodiversity ......................................................................................37 What is Biological Diversity?...................................................................................................................37 The Natural Heritage Ranking System .....................................................................................................38 APPENDIX B - SITE PROFILE...........................................................................................................................41 APPENDIX C - INVERTEBRATE CHARACTERIZATION ABSTRACTS ..................................................................47 APPENDIX D - SPECIFIC CONTROL METHODS FOR NON-NATIVE SPECIES ......................................................62 APPENDIX E - COMMUNITY CHARACTERIZATION ABSTRACTS ......................................................................67 i TABLES TABLE 1. IMPERILED BUTTERFLY AND SKIPPER SPECIES OCCURRING IN HORSETOOTH MOUNTAIN PARK .....3 TABLE 2. POTENTIALLY PROBLEMATIC NON-NATIVE SPECIES PRESENT AT HORSETOOTH MOUNTAIN PARK OR ADJACENT AREAS ...........................................................................................................................10 TABLE 3. IMPERILED BUTTERFLIES KNOWN TO OCCUR WITHIN HORSETOOTH MOUNTAIN PARK AND PLANTS NEEDED FOR SOME PART OF THEIR LIFE CYCLE .....................................................................................16 TABLE 4. DEFINITION OF COLORADO NATURAL HERITAGE IMPERILMENT RANKS .......................................40 FIGURES FIGURE 1. GRASSLAND, SHRUBLAND, AND FOREST HABITATS AT HORSETOOTH MOUNTAIN PARK. ...............5 FIGURE 2. VEGETATION MAP OF HORSETOOTH MOUNTAIN PARK...................................................................6 FIGURE 3. MEADOW DOMINATED BY SMOOTH BROME IN UPPER SPRING CANYON. .......................................11 FIGURE 4. HOPS – A HOST PLANT FOR AN IMPERILED BUTTERFLY AT HORSETOOTH MOUNTAIN PARK. ........17 FIGURE 5. PRIORITY MANAGEMENT AREAS..................................................................................................23 ii ACKNOWLEDGMENTS We would especially like to thank Daryl Burkhard (Larimer County Parks and Open Lands) for her assistance with this project, especially with input on the implementation steps, and for her continued support of the Colorado Natural Heritage Program. We would also like to thank the following individuals for their valuable input and support during this project: K-Lynn Cameron and Ken Woods (Larimer County Parks and Open Lands); John Fusaro and Harvey Sprock (Natural Resources Conservation Service); Drs. Paul Opler, Boris Kondratieff, Rick Knight, and Rick Laven (Colorado State University); Andy Warren (Cornell University); Ann Armstrong, Steve Armstead, Matt Clausen, and Brad Skowronski (City of Boulder Open Space and Mountain Parks); Cindy Owsley and Laura Deiter (Boulder County Parks and Open Space). iii EXECUTIVE SUMMARY Larimer County Parks and Open Lands is currently in the process of revising the management plan for Horsetooth Mountain Park. As part of that management plan, the Colorado Natural Heritage Program (CNHP) was contracted to identify potential management strategies for improving the health of the shrubland and grassland plant communities, and for protecting imperiled butterflies which are known to be closely associated with these communities. This was done by identifying the goals for these plant communities and species, evaluating pertinent ecological information, identifying stresses to these natural resources, and identifying strategies to address these stresses. Obviously, management decisions will need to be made by Larimer County in the context of multiple use as well as financial, social, and practical constraints. By identifying a wide variety of possible management practices the feasibility of implementing these practices can be addressed by the land managers. Implementation of some management strategies may require changes in funding, public education, or partnerships with other agencies or individuals. Recommendations • Use prescribed burning and grazing to reduce the abundance of non-native species (concentrating on cheatgrass and Canada bluegrass) in the grassland and shrublands. • Use application of herbicides or physical removal to reduce the abundance of non- native species