Decoupled functional and phylogenetic diversity provide complementary information about community assembly mechanisms: A case study of Greek forests

Abstract

Understanding the mechanisms of community assembly is of great importance to biogeography and ecology. Simultaneous investigation of the functional and phylogenetic facets of diversity has been proposed as a useful approach that allows inferences about such mechanisms. This study applies such an approach to explore diversity and structure within and among the main plant community types of mountainous forests in northern and central Greece. Functional and phylogenetic diversity and structure were measured in 25 community types of broadleaved deciduous and mountainous coniferous forests. Functional richness and Faith’s phylogenetic diversity were used to assess diversity, while mean pairwise functional and phylogenetic distances were used to investigate structure. Relationships between both facets of diversity and structure, as well as community types, were tested using boosted regression trees separately for all vascular plant taxa and taxa occurring in the forest understorey. Phylogenetic diversity was positively correlated with functional diversity, but phylogenetic structure was not a good predictor of functional structure. The understorey dataset revealed non-random structure for more vegetation plots than the dataset with all taxa. Habitat effects, represented by community types, were found to be better predictors of functional structure than phylogenetic structure, highlighting the need to account for habitat variability in studies of community assembly. In our study system, the two diversity facets provide complementary information on the structure of community types since most of the vegetation plots studied were found statistically significantly structured for one diversity facet (functionally clustered or phylogenetically overdispersed) and random for the other. Our results indicate that functional and phylogenetic measures provide different insights into the mechanisms driving the assembly of the forest community types studied.