Graduate Thesis Or Dissertation

Geographic variation in distribution and cover of principle native and non-native plant species along gradients of topography, climate, and disturbance in protected-area sagebrush steppe communities of the Columbia Plateau

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  • The sagebrush steppe ecosystem of the Columbia Plateau has become degraded by a long history of alternative land use and associated perturbations. Protection of remnant stands of intact sagebrush steppe currently relies upon their preservation within the nation's network of parks and protected-areas. The John Day Fossil Beds National Monument, located in central Oregon, and Craters of the Moon National Monument and Preserve, located in southeast Idaho provided a unique opportunity to examine the pattern of plant species distribution and invasion dynamics in two Columbia Plateau protected-area landscapes with a mixed history of alternative land management and protection. Non-metric multidimensional scaling and nonparametric multiplicative regression were applied to data from the National Park Service's Inventory and Monitoring program to investigate correlations of native and non-native plant species to environmental and landscape variables. Understanding how these patterns change at the landscape scale and identifying variation in these patterns between landscapes may improve efficacy in resource management planning. Principle native species reviewed included sagebrush species (Artemisia spp.), broom snakeweed (Gutierrezia sarothrae), currants (Ribes spp.), desert sweet (Chamaebatiaria millefolium), dwarf goldenbush (Ericameria nana), green rabbitbrush (Chrysothamnus viscidiflorus), bluebunch wheatgrass (Pseudoroegneria spicata), bluegrass species (Poa spp.), sandberg bluegrass (Poa secunda.), wheatgrass species (Agropyron spp.), Great Basin wildrye (Lymus cinereus), and squirreltail (Elymus elymoides). Principle non-native invasive species reviewed included cheatgrass (Bromus tectorum), medusahead (Taeniatherum caput-medusae), and bulbous bluegrass (Poa bulbosa), tumble mustard (Sisymbrium altissimum), and tansy mustard (Descurainia spp.). The distribution and relative cover of principle species within the John Day Fossil Beds National Monument were found correlated to combined effects of slope and aspect, representing a transition from steep south-facing slopes to steep north-facing slopes. Species cover and distribution were also found to be correlated to crop year precipitation, the amount of rain and snow falling between October and May. Individual species response along topographic gradients revealed higher relative cover of B. tectorum on the more xeric, south-facing slopes and an increase in the cover of P. spicata on more mesic, north-facing slopes. The relative cover of G. sarothrae and T. caput-medusae were found to increase with increasing crop year precipitation. The distribution and relative cover of principle species within Craters of the Moon National Monument were found correlated to a north to south spatial separation of sampling frames. This gradient represented a transition from higher elevation to lower elevation, decreasing moisture availability, and increasing proximity to alternative land use (i.e. grazing, agriculture) and transportation corridors. Individual species response along these topographic and environmental gradients revealed higher relative cover of non-native invasive species in southern portions of the monument and with positive correlation to the more xeric and disturbed portions of the Monument. The results of this study have increased the understanding of species cover distribution across environmental and topographic gradients within protected sagebrush steppe landscapes while providing insight into the applicability of resilience theory to Columbia Plateau ecology.
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