The Effects Of Alien Species On Plant Diversity Patterns Along An Elevational Gradient In MT.Tianmu

As an important part of global change,the invasion and diffusion of alien plants are the key driving factors influencing changes in biodiversity and ecosystem functions.Exploring the elevational pattern of alien plant diversity and its influence on native biodiversity is of great significance to macroecology and biodiversity conservation.This work took Tianmushan National Nature Reserve in Zhejiang Province as the study area.This reserve is located in an area with rapid economic development recently,with rich document in herbarium specimen collection and plant surveys and long history of human activities.Data from the flora of Mt.Tianmu,field surveys,herbarium specimen records and the filed investigations from citizen scientists were compiled and used to map elevational distribution ranges of all alien and native plants.In this study,I compared the elevational patterns of native and alien plant taxonomic and phylogenetic diversity,evaluated how alien plants affect native plant diversity,community composition and phylogenetic structure,and analyzed the main drivers of these diversity patterns,including climate and human disturbance.The main results are below:(1)The flora characteristics of alien plants and native plants were different,mainly reflected in family and genus composition,life form spectrum and distribution type.The proportion of woody plants and tropical distribution genera increased significantly in the alien flora.With the increase in elevation,the abundance of alien plants showed a decreasing trend,mainly concentrated in low-elevation areas with strong human interference.The abundance of native plants showed a unimodal pattern,reaching a peak at 500-600 m elevation.Annual mean temperature,precipitation seasonality and precipitation in the driest month are the main environmental factors limiting plant richness at high elevations.(2)Alien plants increased the β diversity of the community,changed the replacement rule of plant species along the elevational gradient,and increased the spatial heterogeneity of plant diversity.It reduced phylogenetic β diversity and made species at the same elevation more evolutionarily relative,leading to phylogenetic homogeneity.As for the effects of alien species on phylogenetic structure,when estimated with the Net Relatedness Index(NRI),the aggregation trend of community phylogeny was significantly reduced,but there was no significant difference when the Nearest Taxon Index(NTI)was used,and those results differed among different life forms.To conclude,this research demonstrated the elevational gradient pattern of exotic plant diversity and its impact on mountain ecosystems,analyzed the changing rules of species diversity,phylogenetic diversity and phylogenetic community structure,and emphasized the effects of climate and human activities on alien and native plant diversity distribution in subtropical mountain ecosystems.This work provided a scientific basis for understanding the ecological and evolutionary mechanisms behind regional alien plant diversity mediated by human beings.