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Effects of Topography and Microclimate on Plant Community Structure in a Great Plains Refugial Forest
Forests harbor considerable biodiversity and regulate climate. However, climate change is restructuring forest vegetation distributions globally, resulting in some plants becoming mismatched with local environments and potentially precipitating species’ range shifts. We lack information on how macroclimatic changes, coupled with topography-driven environmental variation, will modify the local-scale microclimate that plants experience. Here, I assess community structure and function of forest overstory and understory plants in relation to topography-driven microclimatic variation in a refugial forest in the Great Plains. First, I evaluate the effects of topography and microclimate on overstory structure, diversity, and composition. Topography and microclimate strongly covaried along local elevational gradients, with the magnitude of microclimate variation paralleling regional-scale temperature and rainfall variation. Forest structure was more complex and alpha diversity was higher in moister, less-exposed habitats, with strong topography-driven beta diversity. Second, I quantified the influence of overstory and topography on understory microclimate conditions, and on understory plant diversity and composition. Overstory basal area and topography strongly influenced understory microclimate, providing environmental buffering for plants. Understory woody species density and diversity were higher in moist, less-exposed habitats, with substantial topography-driven species turnover. Conversely, C3 and C4 grass diversity was higher in exposed, high-light habitats, and other herbaceous plants exhibited high diversity across a range of topographic habitats. Third, I quantified leaf trait variation across three dimensions of functional trade-offs and assessed the extent to which they shaped trait variation across biological scales. I found woody species investing more resources in leaf productivity had less durable and drought-tolerant leaves with reduced photoprotection, translating to topography-driven, community-level durability-productivity and water limitation tolerance-productivity trade-offs. Forests along desiccation gradients may experience composition shifts, favoring species with durable, drought-tolerant traits. This dissertation illustrates the importance of topographic and microclimatic variation in driving forest plant diversity and distributions, suggesting topography-mediated microclimate refugia will be essential in sheltering plants from macroclimatic changes, and underscoring a need for microclimate monitoring globally to predict responses of forests to climate change.
McNichol, Bailey Holland, "Effects of Topography and Microclimate on Plant Community Structure in a Great Plains Refugial Forest" (2023). ETD collection for University of Nebraska - Lincoln. AAI30569054.