Research On Dynamic Relationship Between Vertical Structure And Species Diversity Of Evergreen Deciduous Broad-leaved Forest Community In Tianmu Mountain By Yikai Lou

As the basis of human survival and development,biodiversity is losing at an unprecedented rate.Understanding the composition mechanism of biodiversity in forest communities is of great significance to the protection of forest biodiversity and sustainable forest management.Based on the survey data of 1hm~2 evergreen deciduous broad-leaved mixed forest plot at the center of Tianmu Mountain in Zhejiang Province in 2012 and 2018,we assessed species biodiversity by K-means clustering method,the individuals with diameter at breast height(DBH)≥1 cm were divided into different forest layers according to tree height,and the features of species richness,species abundance,floristic composition and species diversity in each layer were computed,compared,and contrasted.In addition,the direct and indirect biodiversity impacts were also evaluated by using path analysis,namely,the quantity of decision coefficients,combined with the analysis of the impact of rare species and occasional species on community and each layer.The objective of the study was to reveal the influence of vertical structure on community species diversity in an evergreen deciduous broad-leaved forest community.The results demonstrated that:(1)The forest community had multiple-layered vertical structure,among which there were 4,390woody plants of 2012 with DBH≥1 cm,belonging to 39 families,74 genera and 125 species,and 4406woody plants of 2018 with DBH≥1 cm,belonging to 39 families,76 genera and 119 species.The forest community can be divided into five layers in vertical level:shrub layer,sub-canopy layer,lower canopy layer,middle canopy layer and upper canopy layer.(2)From bottom to top layers,the space of tree height between each layer appeared small at first and then large,and the DBH of each layer increased obviously with the trend of inverted“J”,as well as the species richness and abundance decreased apparently.During 2012-2018,the average tree height and average DBH of the whole community have increased by 20.00%and 8.93%respectively.The growth rate of average tree height and average DBH of each forest layer was as follows:sub-canopy layer>shrub layer>middle canopy layer>upper canopy layer>lower canopy layer.In terms of floristic composition,the geographical distribution of families and genera in the whole forest community and each layer is approaching from temperate distribution to tropical distribution.Among them,the geographical distribution of families and genera in shrub layer and sub-canopy layer is mainly tropical distribution,while the lower,middle and upper canopy layers are mainly temperate distribution.(3)The overall species diversity of mixed forest community in Tianmu Mountain changed little from2012 to 2018,and all three indexes showed an upward trend,among which Shannon-Weiner index,Pielou index and Simpson index increased by 0.24%,1.47%and 0.83%respectively.The absence of forest layer had a certain impact on the whole community more or less.Along the forest layer,the number of common species among different layers gradually decreased but the number of endemic species gradually increased.In addition,the number of common species and endemic species between two adjacent forest layers are also appeared similar trend.There were a certain number of endemic species in each forest layer.The difference of species composition between forest layers improved the species diversity of the community and played a key role in maintaining the species diversity of the community.(4)Shrub layer was the largest contributors to the community overall species diversity index from2012 to 2018 through path analysis of biodiversity of different layers to community overall biodiversity.And the decision coefficient of shrub layer towards overall species diversity of community that Shannon-Wiener index,Pielou index and Simpson index in 2012 was 0.726,0.753,and 0.760,respectively and in2018 was 0.845,0.651 and 0.755 respectively.The decision coefficient of shrub layer was much higher than the other four forest layers,which was major decision variables to maintain the species diversity of the whole community.Besides,the development degree of shrub layer had a decisive and increasing influence on the complexity,uniformity and diversity of mixed forest community.(5)Rare species and occasional species in 2012 and 2018 accounted for 63.49%and 63.03%of the total species in the community respectively,but only 6.85%and 6.06%of the total individuals in the community respectively.Meanwhile,the rare species and occasional species occupied a large amount of species richness in the whole community and each forest layer,and the lack of rare species and occasional species resulted in the decrease of species diversity of both the whole community and each layer,which also had an impact on Margalef richness index,Shannon-Wiener index and Simpson index from large to small.In conclusion,the vertical structure of the community was critical in maintaining the overall species diversity of the given forest community.The shrub layer played a decisive role in the composition of overall species diversity,besides the number of occasional and rare species also played a key role on the composition,thus,species diversity of the community.