Absence of a Grass/Fire Cycle in a Semiarid Grassland: Response to Prescribed Fire and Grazing |
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| Authors: | Christopher J. McDonald Guy R. McPherson |
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| Affiliation: | 1. Natural Resource Advisor, University of California, Cooperative Extension, San Bernardino, CA 92415, USA;2. Professor Emeritus, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 85721, USA;1. Student Researcher, University of California Berkeley, Department of Environmental Science, Policy and Management, Berkeley, CA 94720, USA;2. Postdoctoral Researcher, University of California Berkeley, Department of Environmental Science, Policy and Management, Berkeley, CA 94720, USA;3. Professor, University of Colorado Boulder, Department of Ecology and Evolutionary Biology, Boulder CO 80309-0450, USA;1. US Geological Survey, Southwest Biological Science Center, Moab, UT 84532, USA;2. Department of Physical and Environmental Sciences, Colorado Mesa University, Grand Junction, CO 81501, USA;3. US Geological Survey, Forest and Rangeland Ecosystem Science Center, Corvallis, OR 97330, USA;1. Department of Agronomy and Horticulture, University of Nebraska-Lincoln, Lincoln, NE 68583, USA;3. Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801, USA;4. Department of Sociology, Iowa State University, Ames, IA 50011, USA;1. Udall Center for Studies in Public Policy, University of Arizona, Tucson, AZ 85719, USA;2. Arid Lands Resource Sciences, University of Arizona, Tucson, AZ 85719, USA;3. School of Natural Resources and the Environment, University of Arizona, Tucson, AZ 85719, USA;1. Brackenridge Field Laboratory, University of Texas at Austin, Austin, TX 78703, USA;2. El Coyote Ranch, Carrizo Springs, TX 78834, USA;3. El Coyote Ranch, Riviera, TX 78379, USA |
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| Abstract: | Many nonnative invasive grasses alter fire regimes to their own benefit and the detriment of native organisms. In southern Arizona the nonnative Lehmann lovegrass (Eragrostis lehmanniana Nees) dominates many semiarid grasslands where native grasses were abundant. Managers are wary of using prescribed fire in this fire-prone community partly due to the perceived effects of a grass/fire cycle. However, examples of the grass/fire cycle originate in ecosystems where native plants are less fire-tolerant than grasses and the invasive plant does not mimic the physiognomy of the native community. We investigate the effects of prescribed fire and livestock grazing on a semiarid grassland community dominated by a nonnative invasive grass. Lehmann lovegrass does not appear to alter the fire regime of semiarid grasslands to the detriment of native plants. Prescribed fire reduced the abundance of Lehmann lovegrass for 1 to 2 yr while increasing abundance of native grasses, herbaceous dicotyledons and fall richness, and diversity. Effects of livestock grazing were less transformative than the effects of fire in this long-grazed area, but grazing negatively affected native plants as did the combination of prescribed fire and livestock grazing. Although Lehmann lovegrass produces more fuel than native plants, fire frequency in semiarid grasslands appears to be limited by the paucity of above-average precipitation, which constrains high fuel loads. In addition, many native grasses tolerate high temperatures produced by Lehmann lovegrass fires. Consistent with previous research, fire does not promote the spread of Lehmann lovegrass, and more importantly human alteration of the fire regime is greater than the nominal effects of Lehmann lovegrass introduction on the fire regime. |
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