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Abstract
In this dissertation, I describe the relationships between mature trees and seedlings in Northeast Georgia temperate forests, with a focus on how tornado disturbance can alter plant-soil relationships. I used field observations to assess spatial patterns between trees and same-genus seedlings in a Piedmont forest. A greenhouse experiment was used to examine differences in plant-soil feedbacks between tornado-damaged and intact Southern Appalachian forest areas. That experiment was followed by a two-part field transplant experiment which assessed the role of soil biotic feedbacks in a tornado-damaged landscape. In the first study, I observe patterns of seedling mortality near mature trees of the same genus in a mapped Piedmont forest. I use a spatially-explicit approach to examine shifts in seedling spatial patterns and effects of neighboring trees on seedling performance. The findings are consistent with negative distance dependence patterns at the genus level. Shifts in seedling spatial distributions, seedling survival rates, and seedling survival probabilities supported the hypothesis that seedlings in this forest are negatively impacted by the influence of closely related trees. In the second and third studies, I document changes to plant-soil feedbacks in a tornado track in the Southern Appalachian Mountains. The second chapter uses a greenhouse study to examine plant-soil relationships for common Southern Appalachian tree species and whether those relationships are neutral in tornado-damaged patches. The results suggest that plant-soil feedbacks are not neutral, but instead highly variable after severe wind disturbance. The nature of plant-soil feedback changes depended upon species identity. The third chapter uses a two-part greenhouse and field experiment to compare effects of soil biotic conditioning and the abiotic environment on seedling growth and survival in tornado-damaged forest areas. Four years after a tornado, plant soil interactions for common southern Appalachian seedlings were to be the same in both intact- and tornado-damaged forest areas. While some plant-soil feedbacks are visible in the field, they were secondary determinants of seedling performance. Seedling survival was more affected by abiotic environmental characteristics regardless of soil inoculum origin. Overall, plant-soil feedbacks calculated from seedlings grown in the greenhouse did not match those calculated from field-transplanted seedlings.