Community Assembly and Vegetation Patterns Across Space and Time in the Longleaf Pine Ecosystem

Community assembly is the process in which species are filtered into ecological communities. Multiple processes, which often operate at different spatial and temporal scales, are thought to act synergistically to influence the number and identity of species in local communities. Thus, a key challenge in ecology is to identify those processes and determine their relative importance. Here, I document vegetation patterns in the longleaf pine ecosystem and quantify the relative importance of multiple ecological processes structuring those patterns. Chapters 2 and 3 explore how fire frequency, soil properties, and drought have influenced species richness and composition patterns across ~ 20 years in longleaf pine plant communities located in southeastern North Carolina. This work also informs land management agencies on best practices for implementing prescribed fire to maintain plant species richness. Chapter 4 uses 849 vegetation plots to determine how soil properties, climate, and biogeographic history simultaneously shape species richness across the longleaf pine range. This work reflects on where species richness is highest and identifies what processes drive differences in species richness across latitude. Chapter 5 uses species co-occurrence metrics to quantify the relative importance of stochastic processes in assembling longleaf pine plant communities by examining whether competition, environmental filtering, and stochastic processes shift in relative importance across an environmental gradient. Chapter 6 synthesizes the processes that assembly longleaf pine communities and then extends those findings by drawing parallels to other species-rich grasslands. Local environmental filtering (e.g., soil properties) emerged as the most consistent and important factor structuring both species richness and species composition patterns across time and space. However, competition, climate, stochastic processes, fire frequency, and biogeographic history explained additional variation in species richness and composition unaccounted for by soil properties. As predicted, the relative importance of processes changed with spatial scale: environmental filtering became more important at larger spatial grains, while competition, stochasticity, and fire frequency became more important as spatial grain decreased. Thus, these results suggest vegetation patterns and their drivers are scale-dependent and community patterns in the longleaf pine ecosystem are shaped concurrently and in an often complex fashion by multiple processes.Doctor of Philosoph