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Fiona Noonan Thesis Final

March 11 @ 3:00 pm - 4:00 pm MST

Shifting disturbance regimes, shifting ecotones: The influences of wildfire, climate, and restoration on Northern Great Basin plant species distributions

Abstract: Distributions of important rangeland species in the Great Basin—including sagebrush (Artemisia spp.), conifers (Juniperus spp., Pinus spp.), and invasive annual grasses (e.g. Bromus tectorum)—are shifting due to changes in fire regimes, invasive species dynamics, human land use, and the climate. Characterizing how these overlapping disturbances influence species abundance and distribution is critical for land management decision-making, but the specific interactions between these disturbances and sagebrush systems remain poorly understood. Longstanding observations of conifer expansion and invasion by annual grasses like Bromus tectorum provide evidence of shifting ecotones in the sagebrush-steppe and present associated management challenges. These changes, which both respond to disturbance events and are themselves forms of biotic disturbance, stand to alter the fundamental composition and configuration of sagebrush ecosystems. However, without knowing precisely how or where these changes will occur, most management responses have been reactive rather than proactive. To address this gap, I will model species distributions of common rangeland species in the Northern Great Basin in conjunction with the Bureau of Land Management, the single-largest land manager in the region. This management-oriented approach will ensure my research is informed by real-world concerns while also advancing the use of disturbance-informed, landscape-scale species distribution models. My research will expand on an existing sagebrush species distribution model that improves species predictions by accounting for human-induced factors, such as fire history and restoration treatments. I will build on this fire-and-restoration-informed approach by employing a joint species distribution model, which can account for species co-occurrences and interactions in addition to abiotic disturbance predictors such as fire size and frequency. By incorporating a more robust suite of fire variables and species dynamics into my species distribution model, I expect to further improve predictions of common rangeland species distributions. These results should, in turn, capture the consequences of post-disturbance successional dynamics under changing fire, climate, and invasive species regimes. Additionally, model outputs can inform coordinated conservation actions to maintain and enhance sagebrush ecosystems’ resistance and resilience to ongoing disturbance regime shifts, both now and into the future.

Advisor: Megan Cattau

Co-Advisor: Trevor Caughlin, Jodi Brandt, Brittany Brand