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As biodiversity becomes increasingly threatened by human activities, the need to broaden our understanding of factors that regulate the diversity of ecological communities also becomes more urgent. Diversity has traditionally been quantified with indices based on taxonomic species identities, which grant equal importance to all species and ignore variation in their physical characteristics and biological processes, which may be differentially important to ecosystem function. This problem has been countered with the development of phylogenetic diversity metrics based on the principle that closely related species tend to be more similar in morphology and physiology than distantly related species and thus occupy similar ecological niches. Tests for phylogenetic clustering and overdispersion provide clues about whether community assembly is driven by environmental filtering or competitive interactions. We used sampling data collected across 80 plots in an old-growth Appalachian forest (1979 and 2010) to analyze phylogenetic diversity among midstory (2.5–25 cm diameter at breast height) and overstory (>25 cm dbh) trees to further understand the role of local topographic variation in structuring communities. Midstory and overstory phylogenetic diversity was not significantly related to aspect (all r2 ≤ 0.02, P > 0.11) or slope steepness (all r2 ≤ -0.013, P > 0.36) in either year. We found that the within-plot species assemblages tended to be more phylogenetically clustered at higher elevations (all r2 ≤ 0.34, P < 0.001) in both years, and that this relationship was stronger among overstory trees. This suggests that tree communities at higher elevations experience an environmental filtering effect, resulting in phylogenetic clustering where mature communities contain closely related species with similar adaptations for surviving in xeric conditions. Lower elevation communities contain species that are on average more distantly related and likely represent a more diverse array of functional traits that help to minimize competitive interactions.
Ryan W McEwan
Primary Advisor's Department
Stander Symposium poster
Chapman, Julia I., "Tree Community Phylogenetic Diversity Varies with Topography in an Old-growth Appalachian Forest" (2016). Stander Symposium Posters. 782.