Maintenance of constant functional diversity during secondary succession of a subtropical forest in China

Questions Does the importance of biotic interactions between tree species increase during secondary forest succession? Do functional trait values become increasingly divergent from early towards late successional stages and how is functional diversity affected by trait identity, species identity and species richness effects? Location Gutianshan National Nature Reserve, Zhejiang Province, southeast China. Methods Based on 26 leaf and wood traits for 120 woody species, we calculated functional diversity, using Rao's formula for quadratic entropy, trait dissimilarity, defined as half the mean trait-based distance of all species in the community, and functional evenness, defined as the degree to which functional diversity is maximized. We employed randomization techniques to disentangle the effects of trait identity, species identity and species richness on these three components of functional diversity. Results Against expectations, functional diversity did not show any successional trend because the communities compensated for a loss in trait dissimilarity by distributing the trait values more evenly among the resident species, thus increasing functional evenness. Randomization tests showed that functional diversity was not affected by trait identity, by species identity or by species richness, which indicates that functional diversity was neither determined by particular single traits or by single species with outstanding trait values. Conclusions The constant functional diversity suggests constant functionality in this subtropical forest, which might temporally maintain stable immigration conditions during the course of succession, and thus provides an explanation why these subtropical forests become more species-rich with time.