Effects Of Topographic Heterogeneity On Quantity Characteristic Of Woody Plants Community In Jianfengling Tropical Montane Rainforest

Species coexistence is one core content of community ecology.It is increasingly recognized that one of the critical challenges is to evaluate the respective contributions of different environmental factors to species coexistence.In this study,the 60 hm² tropical montane rainforest plot of Jianfengling was classified into four topographies?low valley,steep slope,upper valley,ridge?based on elevation,convexity and slope of each of the 20 m×20 m quadrats by fuzzy C-mean clustering method.Based on the first census in the Jianfengling 60 hm2 tropical montane rainforest plot,we compared differences in community composition and structure,species diversity,aboveground biomass under different topographic conditions.Using Torus-translation tests,we compared the habitat associations of 230 common species from two different perspectives of abundance and aboveground biomass.To preliminarily explore how species-habitat associations change during their three growth stages in Jianfengling plot,habitat associations of 42 dominant canopy trees were tested.It is aimed to provide scientific basis for further study of species coexistence in tropical montane rainforest.The main results are listed as follows:?1?Tree density in the steep slope and ridge were significantly higher than in low valley and upper valley with P<0.05.Many light-demanding species were more abundant in the steep slope and ridge,while shade tolerated species Blastus cochinchinesis and Pinanga baviensis were found in the top 10 dominant species in two valley types.All of these inferred that available light may be one key environmental factor that affects the plant distribution in Jianfengling plot.The species richness and Shannon-Winner index in the steep slope and ridge at 20 m × 20 m scale were significantly higher than those in the two valleys?P <0.05?,while there were no significant difference between the two valleys or between the steep slope and ridge?P <0.05?.The Simpson index was significantly larger in the steep slope and ridge than in the upper valley,and it was the least in the low valley?P <0.05?.Pielou's evenness index was the largest in the steep slope and the lowest in the low elevation valley,and it was significantly higher in the steep slope and ridge than the two valleys?P <0.05?By comparing species-area relationships among these four topographies,when the sampling area was more than 5000 m²,the number of species in the low valley was the largest.But there were no differences among other three topographies,because the numbers of species of them fell within the expected values of the steep slope ±1.96íSE.By comparing the cumulative species-individual relationships among these four topographies,the cumulative rate of the low valley was the largest.In the plot the average aboveground biomass,vegetation biomass and carbon pool of woody plants were 368.8 Mg·hm^-2,457.3 Mg·hm^-2,228.6 Mg·hm^-2,respectively,which showed that the Jianfengling tropical montane rainforest had higher vegetation biomass.In the low valley aboveground biomass(322.3 Mg·hm^-2),vegetation biomass(399.5 Mg·hm^-2)and carbon pool(200.0 Mg·hm^-2)were the lowest,but they were highest in the ridge,with 408.5 Mg·hm^-2,506.5 Mg·hm^-2,253.3 Mg·hm^-2,respectively.The aboveground biomass,vegetation biomass and carbon pool in the steep slope and ridge were significantly higher than those in two valleys?P<0.05?,which also showed that the light affected the plants distribution pattern in Jianfengling plot.?2?Using Torus-translation tests,we examined the relationships between micro-topography and the distribution of 230 wood species with number of individuals larger than 60 and DBH?1 cm in the plot.In terms of species abundance,207?90% of all?of 230 common species showed significant associations with the topographies,and the extent that species-topography associations contributed to species coexistence was 24.5%.In terms of species aboveground biomass,172?74.8% of all?of 230 common species showed significant associations with the topographies,and the extent that species-topography associations contributed to species coexistence was 19.7%.The habitat associations of species were significantly different based on abundance and biomass analyses,which indicated that more abundance do not mean more biomass,and less abundance do not also mean less biomass.Therefore,we should explore the impact of ecological processes on species coexistence from different perspectives.From these two perspectives,we found that topography was one of the important environmental factors that determined species distribution in Jianfengling 60 hm2 plot.Topographic habitat heterogeneity has important contribution in maintaining species diversity in this tropical montane rainforest.?3?Torus-translation tests were conducted for 42 dominate canopy species ranked in the top 30 in aboveground biomass in one or more topographies across different growth stages.The results indicated the number of species significantly associated with topographies was 28 for the saplings,34 for the juveniles and 24 for the adults based on abundance,while based on aboveground biomass it was 28,32,23 correspondly.In terms of positive associations,more than half of significant associations with the same topography for the saplings were the same for juveniles,but few of the associations were sustained for the adults.These results indicated species ecological habitat preferences were different for developmental stages.In terms of negative associations,most of the associations at the saplings were maintained from the saplings to the juveniles within the same habitat,but only just 23% of associations with that habitat were further maintained for the adults.It indicated that topographic limitation on most species showed consistency from the saplings to the juveniles,but differed for the adults.And it is interesting that the extent of topographic habitat heterogeneity contributed to 42 canopy species coexistence was 23.2% for the saplings and 29.2% for the juveniles,but only 13.1% for the adults based on abundance,while based on aboveground biomass it was 20.8%,28.0% and 11.3%,correspondly.It showed that for the saplings and juveniles,habitat filtering played an important role,but for the adults,niche differentiation gradually played a more important role in species coexistence.