1. Logging is a major driver of tropical forest degradation, with severe impacts on plant richness and composition. Rarely have these effects been considered in terms of their impact on the functional and phylogenetic diversity of understorey plant communities, despite the direct relevance to community reassembly trajectories. Here, we test the effects of logging on functional traits and evolutionary relatedness, over and above effects that can be explained by changes in species richness alone. We hypothesised that strong environmental filtering will result in more clustered (under-dispersed) functional and phylogenetic structures within communities as logging intensity increases. 2. We surveyed understorey plant communities at 180 locations across a logging intensity gradient from primary to repeatedly-logged tropical lowland rainforest in Sabah, Malaysia. For the 691 recorded plant taxa, we generated a phylogeny to assess plot-level phylogenetic relatedness. We quantified 10 plant traits known to respond to disturbance (dispersal mode, fruit type, life-history mode, pollination syndrome, reproduction strategy and seed number) and affect ecosystem functioning (plant growth form, plant height, specific leaf area and wood density), and tested the influence of logging on functional and phylogenetic structure. 3. We found no significant effect of local- or landscape-scale forest canopy loss, or configuration of logging roads on species richness. By contrast, both the trait dispersion index (FDis) and net relatedness index (NRI) for phylogenetic dispersion showed strong gradients from clustered towards more randomly-assembled communities at higher logging intensity, independent of variation in species richness. All functional traits showed significant phylogenetic signals, indicating strong concordance between functional and phylogenetic dispersion. 4. Synthesis. We found a strong logging signal in the functional and phylogenetic structure of understorey plant communities, over and above species richness, but this effect was opposite to that predicted. Logging increased, rather than decreased, functional and phylogenetic dispersion in understorey plant communities. This effect was particularly pronounced for functional response traits, which directly link disturbance with plant community reassembly. Our study provides novel insight into the way logging affects understorey plant communities in tropical rainforest and highlights the importance of trait-based approaches to improve our understanding of the broad range of logging-associated impacts.

Plot characteristics for understorey vegetation plots in BorneoThis csv file contains the full database of characteristics for each of 180 vegetation plots including logging metrics, environmental variables as well as taxonomic, functional and phylogenetic diversity indices for understorey plants in Borneo.PlotData.csvSpecies trait data for understorey plant species in BorneoThis csv file contains the complete list of species (691) sampled across 180 vegetation plots (2 x 2m) located at the Stability of Altered Forest Ecosystems (SAFE) project in Sabah, Malaysia, including their allocation to a range of plant functional traits as well as a distinction between native or exotic species origin.SpeciesTraitData.csvMatrix of biomass values for 691 species in 180 understorey vegetation plots in BorneoThis csv file contains a matrix of biomass values for 691 plant taxa sampled across 180 vegetation plots (2 x 2m) located at the Stability of Altered Forest Ecosystems (SAFE) project in Sabah, Malaysia.PlotSpeciesData.csv