Multi-dimensional And Multi-scaled Diversity Distribution Patterns And Their Driving Mechanisms Of Fragmentated Forest Communities

Aim It remains a major challenge to understand the long-term trajectory of community assembly after habitat fragmentation.In real situation,the variance in time after disturbances and the heterogeneity of the initial conditions make it difficult to conduct the comparative study of community assembly trajectories in the fragmented and the intact systems.Here,I have overcome these problems in a novel way which uses a system of islands and adjacent continental habitats with common initial conditions of the plant community assembly.The system was created after the large-scale cutting of forests during the construction of the Xin'anjiang hydroelectric dam in 1959,forming fragmented landscapes in the Thousand Island Lake region.Half a century later,from the perspective of taxonomic,phylogenetic structure and functional traits,we explored the distribution patterns of the biodiversity,community assembly trajectories and the process of divergence of the forest communities on islands and adjacent continental habitats in the Thousand Island Lake region.Location Thousand Island Lake region,Chun'an County,Zhejiang Province,China.Methods We investigated woody plant communities on 26 islands and 26 adjacent mainland plots,and characterized 12 functional traits on the species level(total number of individuals of 91 woody plant species with DBH ?1cm > 46,000).In this study,(1)we calculated several functional indices(functional richness index,functional evenness index,functional divergence index and community-weighted mean value)and used generalized linear models to test the response of the functional traits,on the community level,of island and mainland sample plots to environmental gradients;(2)we used variance partitioning analysis to distinguish the major environmental and spatial drivers of compositional differences of species,and explored the relative contribution of dispersal limitation and habitat filtering between the community assemblies of island and mainland plots;(3)by adopting functional and phylogenetic structure metrics,we explored the relative contribution of habitat filtering and competitive exclusion between the community assemblies of island and mainland plots.Results We found that at the local scale,the effects of fragmentation per se were mainly reflected in the decline of taxonomic and functional ? diversity of the community,simplifying the community structure.At the regional scale,the effects were mainly reflected in the decline of ? diversity,the advantages of dominant species,the scarcity of rare species,and the slowing or even stagnation of succession.Among the 12 functional traits,10 showed significant divergences between the community-weighted mean values of island and mainland plots.Moreover,most traits changed significantly along gradients of soil fertility,which the change traits were also different between different habitats(island vs.mainland).In addition,the species composition of island plots was mainly affected by local environmental factors,suggesting the importance of environmental filtering,while the species composition of mainland plots was mainly affected by spatial factors.Finally,functional and phylogenetic structure dispersion values of most island and mainland plots did not deviate significantly from the random expectation.Main conclusions This study shows that habitat fragmentation per se has a strong negative impact on biodiversity.The trait-environment relationship in fragmented habitats was divergent.The lower biodiversity in fragmented habitats is the result of the comprehensive effects of habitat filtering,competitive exclusion,and dispersal limitation.These findings help to deepen the understanding of how habitat fragmentation affects community assembly.