The Relationship Among Plant Diversity,Environmental Factors And Above-ground Biomass In Tropical Cloud Forest Of Hainan Island

Tropical montane dwarf forest is a typical tropical cloud forest.Testing the relationship between plant diversity,environment and ecosystem functioning can help the forest conservation and management with the compelling evidence of global change.In this paper,we aimed to explore the change of plant species diversity,functional diversity,phylogenetic diversity and environmental factors across the three tropical cloud forest communities in Bawangling,Jianfengling and Limushan of Hainan Island,by surveying the plant species diversity,functional diversity and environmental factors and constructing phylogenetic trees using the species data and Angiosperm Phylogeny Group ?(APG ?)phylogeny.We also tested the effects of species diversity,functional diversity,phylogenetic diversity and environmental factors on above-ground biomass.Results were listed as follows.1)The tropical cloud forest in JFL had the highest values of species abundance and richness whereas LMS had the lowest values.Both the Bray-Curtis and Jaccard dissimilarity coefficients had the different change at three scales with BWL had the lowest values.The functional evenness(FEve)within communities was the maximum while Rao's quadratic entropy(RaoQ)and the mean pairwise trait distance among communities were the minimum in JFL.BWL had the highest values of RaoQ and mean pairwise trait distance among communities,and the lowest values of FEve.LMS had the highest values of mean nearest-neighbor trait distance among communities.The index of functional richness(FRic)also had the different change at three scales with JFL had the lowest values.The mean pairwise phylogenetic distance within and across communities were the maximum in JFL,while the mean nearest-neighbor phylogenetic distance within communities was the minimum,indicating that there were two patterns including phylogenetic clustering and overdispersion in JFL.BWL had the highest values of Faith phylogenetic diversity(PD)within communities and mean nearest-neighbor phylogenetic distance among communities,showing phylogenetic structure was overdispersed.LMS had the lowest values of PD and mean pairwise phylogenetic distance within and among communities,suggesting that phylogenetic structure was clustered.The phylogenetic index of mean nearest-neighbor phylogenetic distance among communities changed differently at three plot sizes.2)We did not find significant differences in above-ground biomass between JFL community(185.8Mg/hm2)and LMS community(195.7 Mg/hm2).But the above-ground biomass in BWL and LMS communities were significantly higher than BWL.The biomass in JFL and LMS forests was mainly contributed by trees with diameter at breast height(DBH)over 30 cm(the proportion is 33.0%and 52.8%respectively).But the biomass in BWL forest was mainly contributed by trees with 5? DBH<10 cm and 10 ? DBH<15 cm(the proportion is 44.1%).3)The canopy openness,soil organic matter,total phosphorous,total nitrogen,available nitrogen,available phosphorous and slope were significantly different among the three tropical cloud forests.The principal component analysis(PCA)and correlation analysis revealed that canopy openness and available nitrogen were the key factors at 5 m× 5 m plot sizes;canopy openness and total phosphorous were the key factors at 10 m x 10 m plot sizes while canopy openness,total phosphorous and slope were the pivotal factors at 20 m × 20 m plot sizes.4)In generalized additive models analysis,the relationship between species richness and above-ground biomass showed a U-shaped curve.Functional richness was linearly correlated with above-ground biomass at 5 m×5 m plot sizes while the relationship of functional richness and above-ground biomass showed a bimodal curve at 10 m ×10 m and 20 m × 20 m plot sizes.The relationship between phylogenetic diversity and above-ground biomass showed an inverse U-shaped curve.What matters the most to above-ground biomass at the relative small scales was species richness and following by functional diversity and phylogenetic diversity,while the functional richness provided more explanations of variation than phylogenetic diversity and species richness at the relative large scales.The combination of the three plant diversity provided more explanations of variation in above-ground biomass than the single one.All three diversity components of plant diversity and environmental factors contributed to explain above-ground biomass and the explanation proportion increased with plot sizes.