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Aspen Ecology in Rocky Mountain National Park: Age Distribution, Genetics, and the Effects of Elk Herbivory

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Aspen Ecology in Rocky Mountain National Park: Age Distribution, Genetics, and the Effects of Elk Herbivory Aspen Ecology in Rocky Mountain National Park: Age Distribution, Genetics, and the Effects of Elk Herbivory By Linda C. Zeigenfuss, Dan Binkley, Gerald A. Tuskan, William H. Romme, Tongming Yin, Stephen DiFazio, and Francis J. Singer Open-File Report 2008–1337 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior DIRK KEMPTHORNE, Secretary U.S. Geological Survey Mark D. Myers, Director U.S. Geological Survey, Reston, Virginia 2008 For product and ordering information: World Wide Web: http://www.usgs.gov/pubprod Telephone: 1-888-ASK-USGS For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment: World Wide Web: http://www.usgs.gov Telephone: 1-888-ASK-USGS Suggested citation: Zeigenfuss, L.C., Binkley, D., Tuskan, G.A., Romme, W.H., Yin, T., DiFazio, S., and Singer, F.J. 2008, Aspen Ecology in Rocky Mountain National Park: Age distribution, genetics, and the effects of elk herbivory: U.S. Geological Survey Open-File Report 2008–1337, 52 p. Available online only Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted material contained within this report. Cover photo courtesy of Carolyn Widman ii Contents Executive Summary............................................................................................................................................................1 Background .........................................................................................................................................................................7 Age Distribution of Aspen...............................................................................................................................................11 Introduction ...................................................................................................................................................................11 Methods..........................................................................................................................................................................12 Age Distribution of Stands ..........................................................................................................................................15 Elk Herbivory Effects on Aspen Stand Regeneration and Growth Rates on Elk Winter Range .........................20 Introduction ...................................................................................................................................................................20 Study Area .....................................................................................................................................................................21 Methods..........................................................................................................................................................................21 Elk Populations ..........................................................................................................................................................23 Climatic and Topographic Conditions ...................................................................................................................24 Statistical Analyses..................................................................................................................................................24 Results ............................................................................................................................................................................24 Elk Herbivory..............................................................................................................................................................24 Aspen Growth............................................................................................................................................................24 Effects of Elk Herbivory on Aspen Regeneration....................................................................................................27 Genetic Diversity, Clone Ages, and Relatedness Within and Between Aspen Stands.......................................30 Introduction ...................................................................................................................................................................30 Overview of the Genetic Concepts and Methods Used in this Study .................................................................31 Molecular Genetics and DNA “Fingerprinting” ..................................................................................................31 Somatic Mutations and the “Molecular Clock”..................................................................................................32 Genets, Ramets, Ortets, and Clones......................................................................................................................32 Diploids, Polyploids, Tetraploids, and Triploids – Why Important? .................................................................33 Materials and Methods ...............................................................................................................................................33 Sample Collection.....................................................................................................................................................33 Laboratory Methods.................................................................................................................................................36 Results and Interpretations of Genetic Studies ......................................................................................................36 Question #1 — Genetic structure and diversity in RMNP aspen populations...............................................36 Question #2 — Techniques for Evaluating Clone Ages and Seedling Recruitment .....................................44 Conclusions and Management Considerations..........................................................................................................47 Acknowledgments............................................................................................................................................................48 References Cited ..............................................................................................................................................................48 iii Figures 1. Random plot locations sampled from a 1-kilometer by 1-kilometer grid across Rocky Mountain National Park, supplemented by additional plots from a 0.5 –kilometer by 0.5-kilometer grid in the low-elevation, east side of the park. ...................................................................................................................................................13 2. Twelve prism points were established at each plot, at 50-meter intervals in a regular triangle ..................14 3. Relationship between tree diameter and age for 647 trees, omitting two trees older than 200 years and trees larger than 50 centimeters in diameter. ........................................................................................................15 4. Across the whole park, the number of aspen per square kilometer (bars) declined exponentially with increasing tree size. ....................................................................................................................................................16 5.Logarithm of number of aspen stems per square kilometer by age class for the two portions of Rocky Mountain National park..............................................................................................................................................17 6. In the lower elevation, east side portion of the park, aspen trees dating after 1920 accounted for 83 percent of trees and 42 percent of basal area .......................................................................................................18 7. Location of aspen stands that were sampled for offtake, recruitment and regeneration, and browse production in 2005 and 2006 in Rocky Mountain National Park. .........................................................................21 8. Location of regenerating and nonregenerating aspen stands in relation to elk groups observed during annual aerial elk population surveys conducted 1994–2007 in Rocky Mountain National Park...................22 9. Mean height of aspen saplings in regenerating and non-regenerating aspen stands of elk winter range of Rocky Mountain National Park..................................................................................................................................26 10. Density of aspen stems in regenerating and nonregenerating aspen stands of elk winter range of Rocky Mountain National Park for all stems less than 2.5 meters height (A) and stems between 1.5 and 2.5 m in height (B) .......................................................................................................................................................................26 12. The relationship between Rocky Mountain National Park winter elk population and annual snowfall from 1965 to 2006 at the Estes Park, Colorado, weather station. ........................................................................28
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