Predicting foundation bunchgrass species abundances: model-assisted decision-making in protected-area sagebrush steppe

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  • Foundation species are structurally dominant members of ecological communities that can stabilize ecological processes and influence resilience to disturbance and resistance to invasion. Being common, they are often overlooked for conservation but are increasingly threatened from land use change, biological invasions, and over‐exploitation. The pattern of foundation species abundances over space and time may be used to guide decision‐making, particularly in protected areas for which they are iconic. We used ordinal logistic regression to identify the important environmental influences on the abundance patterns of bluebunch wheatgrass (Pseudoroegneria spicata), Thurber's needlegrass (Achnatherum thurberianum), and Sandberg bluegrass (Poa secunda) in protected‐area sagebrush steppe. We then predicted bunchgrass abundances along gradients of topography, disturbance, and invasive annual grass abundance. We used model predictions to prioritize the landscape for implementation of a management and restoration decision‐support tool. Models were fit to categorical estimates of grass cover obtained from an extensive ground‐based monitoring dataset. We found that remnant stands of abundant wheatgrass and bluegrass were associated with steep north‐facing slopes in higher and more remote portions of the landscape outside of recently burned areas where invasive annual grasses were less abundant. These areas represented only 25% of the landscape and were prioritized for protection efforts. Needlegrass was associated with south‐facing slopes, but in low abundance and in association with invasive cheatgrass (Bromus tectorum). Abundances of all three species were strongly negatively correlated with occurrence of another invasive annual grass, medusahead (Taeniatherum caput‐medusae). The rarity of priority bunchgrass stands underscored the extent of degradation and the need for prioritization. We found no evidence that insularity reduced invasibility; annual grass invasion represents a serious threat to protected‐area bunchgrass communities. Our study area was entirely within the Wyoming big sagebrush ecological zone, understood to have inherently low resilience to disturbance and resistance to weed invasion. However, our study revealed important variation in abundance of the foundation species associated with resilience and resistance along the topographic‐soil moisture gradient within this zone, providing an important foothold for conservation decision‐making in these steppe ecosystems. We found the foundation species focus a parsimonious strategy linking monitoring to decision‐making via biogeographic modeling.
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  • Rodhouse, T. J., Irvine, K. M., Sheley, R. L., Smith, B. S., Hoh, S., Esposito, D. M., & Mata-Gonzalez, R. (2014). Predicting foundation bunchgrass species abundances: model-assisted decision-making in protected-area sagebrush steppe. Ecosphere, 5(9), art108. doi:10.1890/ES14-00169.1
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  • 5
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  • 9
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  • Funding for this project was provided by the National Park Service Inventory and Monitoring Program, the John Day Fossil Beds National Monument, and the USDA Agricultural Research Service.



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