Influence of Livestock Grazing and Climate on Pinyon Pine (Pinus edulis) Dynamics |
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| Authors: | Nichole N. Barger Henry D. Adams Connie Woodhouse Jason C. Neff Gregory P. Asner |
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| Affiliation: | 1. Assistant Professor, Department of Ecology and Evolutionary Biology, University of Colorado at Boulder, Boulder, CO 80309, USA;2. Graduate Research Assistant, Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA;3. Associate Professor, Department of Geography and Regional Development, University of Arizona, Tucson, AZ 85721, USA;4. Associate Professor, Geological Sciences Department and Environmental Studies Program, University of Colorado at Boulder, Boulder, CO 80309, USA;5. Faculty Scientist, Department of Global Ecology, Carnegie Institution, Stanford, CA 94305, USA.;1. Research Entomologist, U.S. Department of Agriculture, Agricultural Research Service, Northern Plains Agricultural Research Laboratory, Sidney, MT 59270, USA;2. Rangeland Ecologist, U.S. Department of Agriculture, Agricultural Research Service, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT 59301, USA;1. Assistant Range Trend Project Leader, Utah Division of Wildlife Resources, Great Basin Research Center, Ephraim, UT 84627, USA;2. Professor, Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA;3. Research Assistant Professor, Jornada Experimental Range, New Mexico State University, Las Cruces, NM 88003–8003, USA;4. Assistant Professor, Department of Forest, Rangeland, and Fire Sciences, University of Idaho, Moscow, ID 83844-1133, USA;5. Research Assistant, Department of Plant and Wildlife Sciences, Brigham Young University Provo, UT 84602, USA;6. Research Assistant, Madison, WI 53713, USA;7. Associate Professor, Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA;8. Associate Professor, Department of Statistics, Brigham Young University, Provo, UT 84602, USA;9. Post-Doctoral Research Associate, Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA;1. U.S. Geological Survey, Southwest Biological Science Center, Flagstaff, AZ 86001, USA;2. U.S. Geological Survey, Southwest Biological Science Center, Moab, UT 84532, USA;3. Natural Resources Conservation Service, Richfield, UT 84701, USA;1. Research Associate, Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA;2. Professor, Department of Plant and Wildlife Sciences, Brigham Young University, Provo, UT 84602, USA;3. Associate Professor, Department of Statistics, Brigham Young University, Provo, UT 84602, USA.;1. Director of Conservation Ecology, The Nature Conservancy, Reno, NV 89501, USA;2. Ecologist, Eastern Nevada Landscape Coalition, Ely, NV 89315, USA;1. Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86011, USA;2. Center for Ecosystem Science and Society, Northern Arizona University, Flagstaff, AZ 86011, USA |
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| Abstract: | Over the last century there has been marked expansion and infilling of pinyon (Pinus spp.)–juniper (Juniperus spp.) woodlands into grassland and shrubland ecosystems across the western United States. Although range expansions in pinyon-juniper populations have been documented with changing climate throughout the Holocene, over the last century, local scale impacts such as livestock grazing, changes in fire regimes, and increasing atmospheric CO2 concentrations are thought to be more recent drivers of pinyon-juniper woodland distribution. Our objective was to examine the role of historical livestock grazing relative to past climate in regulating pinyon (Pinus edulis Engelm.) recruitment and growth over the last century in a persistent pinyon-juniper woodland. We compared pinyon dynamics on a remote mesa site, minimally grazed by domestic livestock, to a nearby historically grazed site in southeastern Utah. The presence of a significant number of old trees (> 200 yr) at both sites suggests that these populations were well established prior to the 20th century. No differences in pinyon density or basal area were observed between grazed and ungrazed sites. Stand age structure data showed that pinyon recruitment across these sites was highly synchronous, with a large recruitment event occurring during the early 1900s; 17% of the pinyons on both sites dated to the 1920s. Climatic conditions during this decade were consistently cool and wet—conditions known to support enhanced recruitment and growth in pinyon pines. Pinyon growth was also strongly synchronous across sites (r = 0.96). Pinyon growth was significantly correlated with winter/spring precipitation and negatively correlated with June temperature. Taken together, our results suggest that past climate may be more important in structuring pinyon populations than historical land use in these persistent pinyon-juniper woodlands. Given future climate projections of increasing temperature and more extended drought periods, regeneration of pinyon populations following the recent regional-scale dieback may be slow. Moreover, prolonged drought combined with potentially slow regeneration times for pinyon under future climate scenarios could result in substantial declines in pinyon populations across the region, a result that land managers should consider when planning for future restoration treatments in persistent pinyon-juniper woodlands. |
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