Phylogenetic homogenization of Amazonian tree assemblages in forest islands after 26 years of isolation

Question: Losses in species richness and functional diversity of tree assemblages have often been observed in Neotropical fragmented landscapes, but the way in which tree phylogenetic diversity responds to forest insularization over decadal timescales remains unclear. Here, we examine how tree phylogenetic diversity and structure have responded to profound landscape alteration and subsequent non-random species losses within forest islands created within a vast hydroelectric reservoir. Location: Balbina Hydroelectric Dam Reservoir, Central Brazilian Amazonia. Methods: We used a large tree data set including 435 subplots of 0.05 ha each in 34 forest islands of variable sizes and three continuous forest sites in the Balbina Hydroelectric Dam, which contained 11,000 stems representing 365 species and 188 genera. In each subplot we quantified tree phylogenetic diversity and structure and investigated their relationship with landscape structure metrics and the proportion of species within specific functional groups. Results: We uncovered a reduction in phylogenetic diversity in small (