An unfortunate alliance: Native shrubs increase the abundance,performance, and apparent impacts of Bromus tectorum across a regional aridity gradient |
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| Affiliation: | 1. Department of Biology, York University, 4700 Keele St., Toronto, ON M3J1P3, Canada;2. Department of Animal and Range Sciences, New Mexico State University, 2980 South Espina Street, Las Cruces, NM 88003, USA;3. Division of Biological Sciences and the Institute on Ecosystems, University of Montana, Missoula, MT 59812, USA;1. Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, MG, Brazil;2. Departamento de Biologia Geral, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, Brazil;3. Ecological Networks, Department of Biology, Technische Universität Darmstadt, Darmstadt, Germany;4. Instituto de Biologia, Universidade Federal de Uberlândia, Uberlândia, MG, Brazil;5. Instituto Federal do Norte de Minas Gerais, Campus Diamantina, Diamantina, MG, Brazil;6. Laboratório de Ecologia Isotópica, Centro de Energia Nuclear na Agricultura, CENA, Universidade de São Paulo - USP, Piracicaba, São Paulo, Brazil;1. Department of Wildland Resources and the Ecology Center, Utah State University, Logan, UT 84322, USA;2. Department of Mathematics and Statistics, Utah State University, Logan, UT 84322, USA;3. Department of Watershed Science and the Ecology Center, Utah State University, Logan, UT 84322, USA;4. Climate Adaptation Science Program, Utah State University, Logan, UT 84322, USA;1. US Department of Agriculture–Agricultural Research Service, Fort Keogh Livestock & Range Research Laboratory, Miles City, MT 59301-4016, USA;2. Missoula Parks and Recreation, Conservation Lands Division, Missoula, MT 59801, USA;3. Boise State University, Boise, ID 83725, USA;4. US Geological Survey, Forest and Rangeland Ecosystem Science Center, Boise, ID 83706, USA;5. Montana State University, Bozeman, MT 59717, USA;6. Thunder Basin Grasslands Prairie Ecosystem Association, Bill, WY 82633, USA;7. MPG Ranch, Missoula, MT 59801, USA;1. Plant Physiologist, US Department of Agriculture (USDA)−Agricultural Research Service (ARS), Northwest Watershed Research Center, Boise, ID 83702, USA;2. Plant Sciences Technician, US Department of Agriculture (USDA)−Agricultural Research Service (ARS), Northwest Watershed Research Center, Boise, ID 83702, USA;3. Professor, Department of Geosciences, Boise State University, Boise, ID 83725, USA;4. Ecologist, USDA-ARS Range and Meadow Forage Management Research Unit, Burns, OR 97720, USA;5. Geneticist, USDA-ARS Agricultural Genetic Resources Preservation Research Unit, Fort Collins, CO 80521, USA;6. Research Physical/Data Scientist, US Geological Survey, Earth Resources and Observation Science (EROS) Center, Sioux Falls, SD 57198, USA;7. PhD student, Department of Geosciences, Boise State University, Boise, ID 83725, USA;8. Research Geographer, US Geological Survey, Earth Resources and Observation Science (EROS) Center, Sioux Falls, SD 57198, USA;9. Boise Center Aerospace Laboratory Manager, Department of Geosciences, Boise State University, Boise, ID 83725, USA;10. Rangeland Management Specialist, USDA-ARS Rangeland and Pasture Research Unit, Woodward, OK 73801, USA;11. Research Civil Engineer, US Department of Agriculture (USDA)−Agricultural Research Service (ARS), Northwest Watershed Research Center, Boise, ID 83702, USA |
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| Abstract: | Interspecific facilitation contributes to the assembly of desert plant communities. However, we know little of how desert communities invaded by exotic species respond to facilitation along regional-scale aridity gradients. These measures are essential for predicting how desert plant communities might respond to concomitant plant invasion and environmental change. Here, we evaluated the potential for Bromus tectorum (a dominant invasive plant species) and the broader herbaceous plant community to form positive associations with native shrubs along a substantial aridity gradient across the Great Basin, Mojave, and San Joaquin Deserts in North America. Along this gradient, we sampled metrics of abundance and performance for B. tectorum, all native herbaceous species combined, all exotic herbaceous species combined, and the total herbaceous community using 180 pairs of shrub and open microsites. Across the gradient, B. tectorum formed strong positive associations with native shrubs, achieving 1.6–2.2 times greater abundance, biomass, and reproductive output under native shrubs than away from shrubs, regardless of relative aridity. In contrast, the broader herbaceous community was not positively associated with native shrubs. Interestingly, increasing B. tectorum abundance corresponded to decreasing native abundance, native species richness, exotic species richness, and total species richness under but not away from shrubs. Taken together, these findings suggest that native shrubs have considerable potential to directly (by increasing abundance and performance) and indirectly (by increasing competitive effects on neighbors) facilitate B. tectorum invasion across a large portion of the non-native range. |
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