Patterns of phylogenetic relatedness of angiosperm woody plants across biomes and life‐history stages

Abstract

AbstractAimThe tropical niche conservatism (TNC) hypothesis predicts that species in colder or drier climates should on average be more closely related to each other (more phylogenetically clustered) than those in warmer or wetter climates, but a global test of this prediction for local forest communities is lacking. In this study, we test this prediction by analysing a comprehensive dataset of forest communities that covers all forest biomes across the world. Furthermore, within a forest community, vegetation layers from understorey to canopy could be considered a gradient of biotic interaction, on one hand, and an environmental gradient, on the other hand. We assess trends of phylogenetic relatedness of tree species across strata of forests in different forest biomes across the world.LocationGlobal.MethodWe analysed 186 forest plots, each being 0.1 ha in size. For each forest plot, we divided stems into three stem‐size classes. Net relatedness index (NRI) and nearest taxon index (NTI) for angiosperm woody plant assemblages were calculated for each forest plot and for each stem‐size class of the plot. NRI and NTI of forest plots were related to temperature and precipitation in the framework of Whittaker's biome system.ResultsWhen both deep and shallow evolutionary histories of woody species were considered, angiosperm woody plants tended to be more closely related in colder and/or drier climates. Phylogenetic relatedness was greater (i.e. more phylogenetic clustering) among trees with larger stems than among trees with smaller stems at the global scale.Main conclusionsOur finding that species are more closely related towards colder and/or dryer biomes is consistent with the prediction of the TNC hypothesis. The pattern of increasing phylogenetic relatedness towards the upper canopy layer of a forest is stronger in temperate compared to tropical regions, suggesting stronger environmental filtering in the more stressful canopy environment.