Relationship Between Vertical Structure And Plant Species Diversity In An Evergreen Broad-leaf Forest In Tiantong,Zhejiang Province

The forest vertical structure generally refers to the vertical arrangement of all vegetation above the ground.It can directly change the light intensity at different heights in the forest,adjust the temperature and humidity of the understory soil and air,and then affect the seed germination and seedling regeneration understory.Finally,it could adjust theα-diversity of the community through two ways:1)change the overall niche space in the forest.The higher the canopy height of the community,the larger the vertical niche space,and the higher the number of species that the community can accommodate.2)Change the vertical niche filling degree.When the inner space below the canopy is occupied by various species,the vertical niche is fully utilized,and the number of species contained in the community may be higher.At the same time,the greater the difference in vertical structure among communities,the greater the spatial difference of vertical niche,which may eventually affect theβ-diversity of community species composition differences.Therefore,the forest vertical structure may have a great influence on theα-andβ-diversity in forest communities.However,due to the limitation of traditional survey methods,it is not easy to accurately measure the forest vertical structure,which significantly limits our understanding of the relationship between vertical structure and local community diversity.Based on the above,this study was conducted in a 20-hm~2 subtropical evergreen broad-leaf forest permanent plot in Tiantong,Zhejiang Province.It measured the forest vertical structure based on the high-precision point cloud data obtained by UAV-Li DAR.Based on the species composition information of quadrats of different scales,the relationship between vertical structure andα-andβ-diversity of plant communities was assessed by redundancy analysis,regression analysis and variance partitioning analysis,compare the relative importance of vertical structure and ground-level habitat to two types of diversity,and explore the relationship between height structure and internal structure and species diversity.The main results are as follows:（1）There was a significant negative correlation between vertical structure andα-diversity in the Tiantong plot.The more complex the vertical structure was,the lowerα-diversity was.At different plot scales,the vertical structure had a large explanation proportion（21%—70%）for theα-diversity in the plot,which was equivalent to the explanation proportion of ground-level habitat.Both types of vertical structure factors were significantly and negatively correlated withα-diversity,with higher explanations for forest height structure（R~2=0.28—0.45）and lower explanations for forest internal structure（R~2=0.013—0.16）.At different plot scales,the explanation degree of height structure onα-diversity was always greater than that of internal structure.（2）There was a significant positive correlation between vertical structure difference andβ-diversity in the Tiantong plot.The greater the vertical structure difference among communities,the greater the species composition difference.The vertical structure had a larger explanation proportion（28%—58%）for theβ-diversity in plots,which was slightly higher than that of ground-level habitat.The vertical structure also deepened our understanding of the spatial structure in previous studies,among which 26.2%—36.0%of the spatial structure’s influence onβ-diversity comes from vertical structure.Community differences of structure factors of two kinds were positively correlated withβ-diversity,and the explanation rates of height structure differences and internal structure differences toβ-diversity were R~2=0.18 and R~2=0.07,respectively.The explanation degree of height structure on theβ-diversity was always greater than that of internal structure at different plot scales.With the increase of plot scale,the explanation degree of height structure onβ-diversity decreased,and the internal structure gradually increased.In summary,this study accurately measured the vertical structure of the Tiantong plot for the first time by UAV-Li DAR.We proved that the vertical structure,which was often neglected in previous studies,had a strong correlation with theα-andβ-diversity.This correlation mainly came from the influence of canopy height.These results indicated that the vertical structure,especially the canopy height,might be one of the main driving forces of the species diversity pattern of forest plant communities.At the same time,we found a negative correlation between vertical structure andα-diversity in the Tiantong plot,which implied that there might be a complex interaction between vertical structure and species diversity.For example,higher canopy height could strengthen the asymmetric competition among tree species,decreasing the number of coexisting species.Lower canopy height might also be associated with higher individual density,thus increasing the number of potential species.Therefore,this study confirmed the importance of vertical structure to forest plant species diversity and updated the conventional understanding of the impact of vertical structure on species diversity.It provided a new idea for further exploration of the influence mechanism of vertical structure on forest species diversity.