From Genes to Ecosystems: Measuring Evolutionary Diversity and Community Structure with Forest Inventory and Analysis (FIA) Data

Forest genetic sustainability is an important component of forest health because genetic diversity and evolutionary processes allow for the adaptation of species and for the maintenance of ecosystem functionality and resilience. Phylogenetic community analyses, a set of new statistical methods for describing the evolutionary relationships among species, offer an innovative approach for assessing the health of forest communities from an evolutionary perspective. Forest Inventory and Analysis data are ideal for conducting phylogenetic community analyses for forest tree species at broad scales. FIA data from 100,000 plots across the conterminous United States were used to investigate the evolutionary characteristics of forest tree communities. This required generating a phylogenetic “evolutionary tree” of the 311 forest tree species inventoried by FIA, based on recent gene sequencing studies of several plant groups. Phylogenetic diversity was quantified for each plot; this statistic sums the evolutionary age of the species present, using the phylogenetic tree. This is a more meaningful way to quantify biodiversity than species richness because, rather than weighting all species on a plot equally regardless of relatedness, it measures their cumulative evolutionary age. General patterns at the ecoregion section scale were similar between mean plot-level species richness and phylogenetic diversity, but important differences also existed. Additionally, the analyses described each plot’s phylogenetic community structure, or whether the species were more clustered or dispersed across the 311-species reference evolutionary tree than expected by chance. The most phylogenetically overdispersed sections were located in the Interior West, while the most phylogenetically clustered included several in the Upper Midwest, New England, California and the Southeastern Coastal Plain. Communities that are phylogenetically clustered consist of more closely related species and therefore may be more susceptible to threats such as pests and climate change. Phylogenetically dispersed communities may be more resilient to these pressures, because greater evolutionary diversity is expected to translate into a greater likelihood that more species will be unaffected by, or will be adaptable to, environmental changes.