Phylogenetic community structure and phylogenetic turnover in the steep monsoon-effected lowland rainforest

Background/Question/Methods

The impacts of winter northeast monsoon reduce local temperature by bringing in cold air, increasing cloudiness and wind chilling. It remarkably influences the vegetation type in Taiwan. The Nanjenshan Forest Dynamics Plot lies on the tropical-subtropical transition zone. The forests of this plot are strongly affected by both seasonal monsoon and typhoons and characterized by extremely high density, low tree height and high degree of canopy openness. The distribution patterns of plant communities are associated with the wind stress gradient caused by the interaction between micro-topography and northeast aspect.

Phylogenetic beta diversity measures how phylogenetic relatedness changes across space. It provides an evolutionary approach to evaluate how community structure as a function of environmental gradients. The phylogenetic tree of Nanjenshan forest was constructed by combining three plant DNA barcodes (rbcL + matK + trnH-psbA). We compared analyses of phylogenetic community structure, phylogenetic diversity, beta diversity and phylogenetic beta diversity across windward and leeward communities in the Nanjenshan plot. The aim of this study is to find the phylogenetic turnover pattern of monsoon-effected communities at small spatial scale.

Results/Conclusions

The higher phylogenetic diversity and species richness were found in the windward communities. The windward communities tended to be dominated by the representatives of different clades, leading to phylogenetic overdispersion towards the tips of the tree. In contrast, the leeward communities showed phylogenetic structure tending toward neutral overall. The phylogenetic beta diversity measured using the nearest neighbor distance metric was lower than when measured using the mean branch-length metric. In addition, the phylogenetic beta diversity was low and beta diversity was relatively high. These patterns mean that the communities have high proportion of closely relative species. We argue that the forests retain multiple different clades to respond relatively rapidly to changing condition across the environmental gradients and the traits that confer fitness in the strong wind niche are evolutionarily labile in the Nanjenshan plot.