Multi-scale Study On Habitat Differentiation Of Semi-humid Evergreen Broad-leaved Forest’s Dominate Tree Species In Central Yunnan

The semi-humid evergreen broad-leaved forest is the representative vegetation type in Central Yunnan.Due to long term deforestation,burning,and understory grazing,the primitive forests of this zonal vegetation are distributed very limited.The study on the habitat characteristics of this kind of vegetation will help to protect and restore it.Castanopsis delavayi and C.orthacantha are the two main dominant species in the semi-humid evergreen broad-leaved forest.In this paper,we applied the Ecological Niche Model,the numeric classification and ordination of the communities,and analysis on habitat features related to tree species to reveal habitat differentiation of these two species.There were three scales that were considered respectively,the ecological geographical distribution of species,the community differentiation,and the habitat differentiation of the tree species.,to conduct a quantitative study on the habitat differentiation of C.delavayi and C.orthacantha.The results were as follows:（1）At geographical distribution scale,the greatest factor influenced on the distribution of C.delavayi was altitude（1400 m–2700 m）,followed by the Mean Temperature of Coldest Quarter（MTCQ）,Temperature Seasonality（TS）,and Annual Mean Temperature（AMT）.The optimum range of MTCQ was 6.5℃-13℃,the optimum TS was 400-520,and the optimum range of AMT was 9℃-16.5℃.C.delavayi was mainly distributed in the Middle of Yunnan,and it had a tendency to expand northward.The most important factor influencing the distribution of C.orthacantha was also altitude,followed by MTCQ,the Precipitation of Driest Month（PDM）,and Soil Silt Particles（SILT）.The optimum range of altitude was 1500 m-2600 m.The optimum MTCQ was 6.5℃-12℃,the optimum PDM was 11mm-15mm,and SILT was 31-39.C.orthacantha was mainly distributed in the Middle of Yunnan,and it had a tendency to expand southward.The two species’high suitable areas overlap by more than 50%.（2）At community level,the results of cluster analysis showed that there were five groups of C.delavayi+C.orthacantha communities in three forests of Luquan County,Xishan,and Jizu mountain,C.orthacantha+Lyonia ovalifolia community;C.orthacantha+Lithocarpus dealbatus community;C.delavayi+Keteleeria evelyniana community;C.delavayi community and Lithocarpus dealbatus community（Mixed C.orthacantha）.According to the plot information of each group,the C.delavayi community mainly concentrated in the altitude of 1930m-2590m,with a slope of 3°-45°,and grew on shadow slope.The communities of C.orthacantha mainly concentrated in the altitude range of 2050m-2810m,the optimum slope was over 20°,and grew on sunny and shadow slope.The ordination results showed that the C.delavayi communities were more concentrated on narrow altitude range,and the C.orthacantha communities were distributed sparsely at lower or higher altitude.The C.delavayi communities were drier than the C.orthacantha communities.The important factors of the community distribution were elevation above see level and slope gradient.Total community coverage changed with the altitude gradient,but community height changed with the slpoe gradient.（3）At tree species individual habitats,the optimum elevation of C.delavayi individual was 2500m-2700m,and the slope gradient range was 15°-25°.In the southeast aspect,there were the maximum number and population density.It occurred more on the convex terrain（-14<TPI<11）and on the partially wet soil.It grew well in the area with moderate stable slope and the highest solar annual radiation(1.9-2.3MJcm^-2a^-1).The optimum elevation of C.orthacantha was 2500m-2700m,and the gradient of the slope was 5°-15°.Large number of individuals was found on northern slope.It usually occurred on the concave terrain（11<TPI<36）.On the place with moisture saturation soil,it grew well.Meanwhile,it prefer moderate stable slope,and the highest solar annual radiation value(1.9-2.3MJcm^-2a^-1).（4）The ecological geographical distribution of C.delavayi and C.orthacantha showed the habitat differentiation.C.delavayi was dominated by altitude and temperature,and C.orthacantha was dominated by altitude,temperature,and precipitation.At the scale of the communities,the elevation was the main factor driving the habitat differentiation,followed by the slope,and the precipitation.On the tree species habitats,the dominants of habitat differentiation were uncertain.But the specific information of habitat was indicated.The characteristics of large scale habitat differentiation can be applied to small scale habitats,and the characteristics of small scale habitat differentiation can be used as a verification and supplement for large scale habitats.（5）The study on the habitat differentiation at the multiple scales indicated that the ecological geographical distribution pattern clearly defined the contribution rate of the bioclimatic factors,and delineated the optimum range,then it could be used to determine the ecological suitable area.Community differentiation were interpreted by the correlation of the environmental gradient variables and community features.The specific value of information can directly reflect the ecological response of the community to environmental differentiation through ordination diagram.As for individual trees,there was a more subtle ecological interpretation of the habitat differentiation of the tree species,but it provided a verification for the previous two scales.The three scales of habitat differentiation had verified the qualitative description of the previous study,and would provide scientific guidance for the restoration and reconstruction of the two forests.