Data from: Using plant functional traits and phylogenies to understand patterns of plant community assembly in a seasonal tropical forest in Lao PDR

Plant functional traits reflect different evolutionary responses to
environmental variation, and among extant species determine the outcomes
of interactions between plants and their environment, including other
plant species. Thus, combining phylogenetic and trait-based information
can be a powerful approach for understanding community assembly processes
across a range of spatial scales. We used this approach to investigate
tree community composition at Phou Khao Khouay National Park
(18°14’-18°32’N; 102°38’- 102°59’E), Laos, where several distinct forest
types occur in close proximity. The aim of our study was to examine
patterns of plant community assembly across the strong environmental
gradients evident at our site. We hypothesized that differences in tree
community composition were being driven by an underlying gradient in soil
conditions. Thus, we predicted that environmental filtering would
predominate at the site and that the filtering would be strongest on
sandier soil with low pH, as these are the conditions least favorable to
plant growth. We surveyed eleven 0.25 ha (50x50 m) plots for all trees
above 10 cm dbh (1221 individual trees, including 47 families, 70 genera
and 123 species) and sampled soils in each plot. For each species in the
community, we measured 11 commonly studied plant functional traits
covering both the leaf and wood economic spectrum traits and we
reconstructed a phylogenetic tree for 115 of the species in the community
using rbcL and matK sequences downloaded from Genebank (other species were
not available). Finally we compared the distribution of trait values and
species at two scales (among plots and 10x10m subplots) to examine trait
and phylogenetic community structures. Although there was strong evidence
that an underlying soil gradient was determining patterns of species
composition at the site, our results did not support the hypothesis that
the environmental filtering dominated community assembly processes. For
the measured plant functional traits there was no consistent pattern of
trait dispersion across the site, either when traits were considered
individually or when combined in a multivariate analysis. However, there
was a significant correlation between the degree of phylogenetic
dispersion and the first principle component axis (PCA1) for the soil
parameters. Moreover, the more phylogenetically clustered plots were on
sandier soils with lower pH. Hence, we suggest that the community assembly
processes across our site may reflect the influence of more conserved
traits that we did not measure. Nevertheless, our results are equivocal
and other interpretations are possible. Our study illustrates some
difficulties in combining trait and phylogenetic approaches that may
result from the complexities of integrating spatial and evolutionary
processes that vary at different scales.