| Reinforced by current climate change,the severe threat caused by human dis-turbance on warm temperate forests has made it one of the most vulnerable com-ponents of the global forest ecosystem.Thus,exploring the coexistence mecha-nism of reginal forest is significant for the biodiversity conservation.Besides,the establishment of forest dynamic plots has provided conditions for exploring the coexistence of species at each scale.This research is based on the data of living trees that grow in 20 ha forest dynamic plot of warm temperate deciduous broad－leaved forest located in Donglingshan,Beijing.It also combines the survey data of coarse wood debris and uses different null models,which are employed to ana-lyze the spatial pattern and the universality of the niche differentiation and nega-tive density dependence(distance dependence and density dependence)in Donglingshan.The aim is to comprehend the role of niche differentiation and neg-ative density dependence in biodiversity conservation and species coexistence in different regions.The main results are summarized as follows:1.The dynamic plot of Donglingshan shows that the temperate component of woody plants is prevailing and the species composition is dominated by deciduous broad-leaved trees.Compared with other dynamics large-scale forests in China,the species richness and abundance of living species are significantly lower than those in the southern subtropical(Dingushan),mid-subtropical plots(Gutianshan),but higher than temperate dynamics plots(Changbaishan).Meanwhile,there was a significant difference in species richness and abundance among different plots in DLS.The levels of vegetation composition was clear,the overall size pattern was gro.Awth-oriented,and the inventory of saplings were abundant,which indi-cated that the community had a good regeneration.Coarse woody debris pattern were as follows:Populus davidiana shows the greatest number of individuals,fol-lowed by Betula dahurica,Quercus wutaishanica and Acer mono.The canopy trees composition of coarse woody debris were predominated in the plot.Besides,the abundance decreased as the size increased,and the size of 5-10 cm with sig-nificant advantages in the abundance.2.The spatial point pattern was used to analyze the distribution pattern of common species in the plot.And the result is that the overall spatial pattern of the living trees was aggregated.As the scale increased,it is from aggregation to sto-chastic;the distribution of living trees also showed an developing pattern,plentiful saplings storage with regeneration in time.As the scale increased,the degree of species aggregation decreased and showed a negative correlation with life form,mean DBH,maximum DBH and species-abundance.The spatial pattern of coarse woody debris was similar to livi’ng trees,and showed aggregate distribution.As the scale increases,it gradually became to random.The coarse woody debris with size of 5-10 cm exhibited higher mortality than others.As the scale increased,the degree of species aggregation decreased and showed a negative correlation’with life form,mean DBH and maximum DBH,while it had a positive correlation with life form.3.The DLS plots was divided into four habitat types:low valley,high valley,low-ridge,and high ridge by multivariate tree analysis.According to the Kruskal-Wallis rank sum test,there was a significant difference between the species com-position and diversity among the four types of habitats.And more species were positively associated with low ridge and negatively associated with high ridge.According to the Totus-translation test,27 species of living trees showed obvious habitat associations,with 25 species present habitat preferences and 16 species present habitat exclusion;for coarse woody debris,with 11 species present habitat preferences and 8 species present habitat exclusion.Out of the 41 species that were detected to be positively associations,only 3 or 2 species showed identical habitat preferences or complete habitat exclusion at different life history stages.The hab-itat associations of most species would change during the growth process,indicat-ing that the niche differentiation at the adult stage is not formed in the time of the sapling.The contribution of niche differentiation to the species coexist is little.4.Based on the null model of independence and the nearest neighbor distance,the correlation of different life history stages was analyzed to deduce whether spe-cies’ spatial dynamics was drived by distance dependence.Living trees showed a strong scale dependence among different life history stages of spatial correlation.Under the small scale,there is the strongest correlation of individual growth stages.On the scale of 0-30 m,80%of the maximum intensity of inter-species association occurred less than 5 m among different life history stages,and 20%occured in the range of 5-10 m.Therefore,the relationship between species is predominantly constrained by distance and it became less connected as the scale increases.The impact of distance on fast-growing species showed greater than that on slow-grow-ing species at all stages.The coarse woody debris present a positive effect on the living trees.Under the scale less than 5 m,there is the greatest correlation,which indicated that the positive effect on living trees posed by the coarse woody debris was also constrained by the distance.In this study,case-control design of random labeling null model was used to leave out the interference caused by habitat heterogeneity.The spatial pattern dif-ferences at different life stages also were analyzed.The result shows that on the scale of 0-30 m,the density-dependent effect existed in each life stages.The larger size pattern was affected by the scale more severely compared to the smaller size.Fast-growing species were prone to be affected by scale at all stages compared to slow-growing species.Besides,the ways that small-size pattern and large-size pat-tern take advantage of habitat are quite distinct.There is a density-dependent effect no matter in small-size pattern or large-size pattern.As the scale became larger,the ways of utilizing habitat in those two patterns tended to be identical,while the density-dependent effect decreased.Which indicated that the density-dependent occurs among adjacent individuals.In general,the negative density dependence effect are common in DLS.They play an important role in maintaining species diversity by regulating the spatial patterns of community,regularizing the large tree space to some extent and re-stricting the grow of the most dominant species to make space and provide re-source for other species.Compared with the niche differentiation(habitat filtering),the contribution of negative density dependent to species coexist in Donglingshan is greater. |
