Maintenance of tree phylogenetic diversity in a highly fragmented rain forest

1. Deforestation and forest fragmentation can drive species to local extinction, potentially changing the phylogenetic community structure and diversity of remaining assemblages. We tested this hypothesis analysing a large vegetation data set from a highly fragmented rain forest. 2. We assessed 9000 trees (both saplings and adults) from 268 species in 45 rain forest patches (ranging from < 1 to 700 ha) in three landscapes with different deforestation levels (4%, 11%, and 24% forest cover) in Los Tuxtlas, Mexico. We tested whether species density (i.e. number of species per unit area) and phylogenetic structure and diversity differed among landscapes, whether they were related to patch area, and whether the relationships differed among landscapes. 3. Overall, the observed differences in sapling and adult species densities across forest patches and landscapes (e. g. lower species densities in smaller patches) resulted in few and very weak changes in the phylogenetic community structure and diversity. Our results indicate that local extirpation of tree species may occur randomly or uniformly (but not in a clustered manner) throughout the phylogenetic tree, supporting the hypothesis of low phylogenetic conservatism of traits associated with vulnerability to forest fragmentation in the Neotropics. 4. Synthesis. This study indicates that in highly deforested and fragmented rain forests, the local extirpation of tree species does not occur across entire lineages. These novel and hopeful findings have direct implications for the ecology and conservation of fragmented rain forests. The maintenance of phylogenetic diversity in highly fragmented landscapes suggests that ecosystem function and stability may be maintained despite the loss of a number of tree species. We argue that in this unique Neotropical region, both large and small rain forest patches are critical for conserving regional tree evolutionary history.