Community Characteristics And Spatial Heterogeneity Of Functional Traits In Coniferous-Broadleafed Mixed Forest Dynamics Plot In Xiaolong Mountain,Gansu Province

Xiaolong Forest Region in Gansu province is one of the most well-preserved areas in the warm temperate-subtropical transition zone of China.Its therefore,provide a natural experimental base for exploring species with intra-specific traits variation(ITV)of wood density in adapting to habitat factors.Therefore,all individuals with diameter at breast height(DBH)≥1 cm were mapped,tagged,and measured in the 6 hm2(300m×200m)forest dynamics plot in Xiaolong Forest Region.Firstly,the species composition,community structure,and habitat preference of dominant species were analyzed.Then,the wood density of all stems DBH≥10cm in the plot were sampled and measured.To determine the degree of variation in wood density within the plot,we used variance decomposition to partition total variance into quadrats(20m ×20m),species,and individuals levels.The relative importance of different habitat factors on the wood density spatial distribution base on community weighted mean(CWM)and community weighted variance(CWV)was studied by using multiple regression analysis.1.A total of 29,251 individuals(41,735 stems)belonging to 33 families,65 genera,and 124 species were identified.The 28 species with importance values ≥ 1 contributed 82.9 % to the total number of individuals.The first four species with the highest importance values were Quercus aliena var.acuteserrata,Betula platyphylla,Lindera aggregata var.playfairii,and Corylus heterophylla.The overall structure of DBH size class of all stems in the plot showed an inverse ‘J’ type which indicated a successful regeneration tendency in the understory.The result of indicator species analysis found that 11 species showed significant habitat preferences,and two species(Ostrya japonica and Acer tetramerum)showed most obvious preferences.The redundancy analysis and partial methods demonstrated that the topographic factors played more important roles in determining species distribution than edaphic factors.2.The variation in wood density was mainly contributed to the differences among species in the Xiaolong dynamics plot,where interspecific variation(71.70%)in wood density was higher than intraspecific variation(28.30%).The influence of abiotic factors on the wood density in quadrats was greater than that of biotic factors.The CWM of wood density showed significant associations with topographic(e.g.elevation)and edaphic(e.g.pH)variables.The quadrats with higher CWM values usually had lower soil pH but higher elevation.Further,the CWV of wood density is positively related to soil pH.Finally,the intraspecific variation had no significant effect on the CWM of wood density,but a significant effect on the CWV of wood density.Thus,there were higher CWV values if we are taken account of intraspecific variation,which indicated an important role of ITV in community assembly.