| Semi-humid evergreen broad-leaved forest(SEBF)is a horizontal zonal vegetation in the central Yunnan plateau,and it is one of the representative and unique types of evergreen broad-leaved forest in western China.Under the influence of monsoon circulation and mountain topography,there is spatial heterogeneity in the geographical distribution of SEBF.In this study,the distribution pattern and its dominant environmental factors of SEBF are analyzed from five aspects: geographical distribution,community distribution,community structure,community species diversity and plant functional characters.The results are as follows:(1)On the geographical distribution scale,there are obvious meridional differences in the potential high-suitable-growth areas of six SEBF constructive species.The highsuitable-growth areas are concentrated in the east and west,and the distribution area in the central region is relatively small.The difference of topography and precipitation is the main factor leading to its niche differentiation.(2)The SEBF in central Yunnan is the most seriously disturbed by human activities.The number of large patches in this area is relatively small,but the number of patches is large,the shape of patches is complex,and the patch connectivity is the lowest,while the SEBF in eastern and western Yunnan is relatively well preserved.Population density and road density are important environmental factors that affect the distribution pattern of vegetation landscape in SEBF.(3)The 295 relevés of SEBF were divided into 26 community types by TWINSPAN.The results of CCA and DCCA showed that the community differentiation was mainly influenced by potential evapotranspiration,aridity index,annual average temperature and precipitation in the coldest season.(4)The 162 plots of SEBF were clustered into 8 groups by UPGMA hierarchical clustering.,The population structures of most constructive species in different SEBF groups were unimodal.There were more seedlings of Pinus yunnanensis in SEBF mixed with P.yunnanensis.The Castanopsis orthacantha Community and C.delavayi Community,which contain more large trees,its population age structure were belong to the declining type.(5)The richness index S and diversity index H of SEBF increased with the elevation.With the increase of longitude,the richness index S declined at first and then rised up,meanwhile the diversity index of other species had no significant change.With the increase of latitude,the richness index S increased significantly,but the species diversity index decreased at first and then increased.RDA ordination results show that the distribution pattern of community species diversity was greatly influenced by annual average temperature,altitude,slope and population density.(6)The leaf area of the five dominant tree species in SEBF,Cyclobalanopsis glaucoides,Lithocarpus dealbatus,Castanopsis delavayi,Cy.delavayi and C.orthacantha,was smaller in central Yunnan(101 E°-102 E °),and higher in latitude areas of 24 N°-25 N°,as well as in altitude areas of 2400m-2700 m.The leaf density was the highest in central Yunnan.The important environmental factors influencing leaf functional traits were topographic factors and climatic factors. |
