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Negative plant-soil feedbacks describe a phenomenon—resulting from interactions between plants and their soil biota, particularly fungal pathogens. These highly dynamic local above- and below-ground interactions may be a way that biodiversity levels are maintained: even if one plant species is a strong competitor, its pathogens suppress its dominance, allowing for the coexistence of multiple plant species. I am interested in how negative feedbacks play a role in determining plant community assembly patterns in a landscape-scale fragmentation field site (Lawrence, Kansas) for which I have over 30 years of historical vegetation data. I built a spatially-explicit cellular automata model of the spatial dynamics of one species, Ambrosia artemisiifolia (common ragweed) over time, across both continuous and fragmented landscapes. Using empirical data from 1985 to set initial conditions, I simulated 32 years of vegetation change and compared the spatial distribution of ragweed in the model to the actual spatial organization of plants from the field site vegetation surveys in 2017. Exploring the spread of ragweed over space and time I asked: as plant communities undergo succession, what spatial patterns of abundance will I observe if negative plant-soil feedbacks are a key driver of plant community composition? Further, how does fragmentation affect these patterns? The model shows that there is a wide range of negative feedback strengths that allow for percent cover levels that resemble the historical data. On the other hand, occupancy, the proportion of samples in which a species is present, requires a much more sensitive range of feedback strengths in order to resemble historical data. In order to yield realistic historical species abundance patterns in the absence of feedbacks, there must be high levels of generalized seed mortality due to other processes. While this model a step towards a more integrated above- and below-ground analysis of spatiotemporal patterns of plant community assembly dynamics, more variables such as abiotic factors, and temporal changes in feedback strength and direction throughout succession must be accounted for, as well as response variables that more accurately represent these patterns.
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Christiana, Lucy D., "Plant-Soil Negative Feedbacks as Drivers of Spatial Patterns of Abundance in a Successional Landscape: A Modeling Approach" (2019). Senior Projects Spring 2019. 45.