Community structure in relation to microtopography in a montane evergreen broadleaved forest in Chebaling National Nature Reserve

Microtopographic factors have a great effect on species composition and diversity patterns of forest communities.Understanding the relationship between microtopographic factors and species patterns will have significant implications for forest conservation and sustainable management.Based on field data collected within a 2-hm2 permanent plot(50 subplots)in the lower subtropical evergreen broadleaved forest in Chebaling National Nature Reserve,Guangdong,China,variations in community structure in response to microtopographic changes were analyzed in five transects from the ridge to the valley that were divided according to sample plot layout,elevational difference,and moisture potential gradient.With contiguous grid quadrat sampling method,species were censused by height,abundance,and percent cover for the understory layer and by height and diameter at breast height(DBH)for the tree layer.Microtopographic attributes including elevation,slope position,aspect and slope degree were also recorded on a subplot basis.The results showed that microtopographic factors had a strong influence on community structure and species distribution.Transect-based mean height and DBH and the proportion of individuals belonging to larger height and DBH class decreased from the ridge to the valley,while species diversity increased gradually.Multi-response permutation procedures(MRPP)indicated that species composition among various transects varied significantly(P 0.0001),and the presence of dominant species and their density also differed greatly.Although tree density varied,both Castanopsis carlesii and Styrax suberifolia were dominant species on all transects.Canonical correspondence analysis(CCA)further confirmed that species had an obvious distribution trend with topographic condition.Photophilous species including Castanopsis carlesii,Castanopsis eyrei,and Lithocarpus glaber tended to distribute on the upslope,while species adapting to warm and humid habitats such as Liquidambar formosana,and Neolitsea chuii became dominant on the valley transects.The Castanopsis eyrei distribution reflected habitat conditions of a higher elevation,whereas the position of Liquidambar formosana and Acer cinnamomifolium in the CCA ordination diagram had an obvious shorter distance to the centroid of downslope.Species including Castanopsis carlesii and Styrax suberifolia,which were widely distributed in the sample plots,occupied important positions in the center of the diagram,indicating the variation in distribution was not obvious with the change of environmental gradient.This study elaborated the response of community composition and structure of a montane evergreen broadleaved forest to microtopographic changes,and will have significant implications both theoretically and in practice for regional biodiversity conservation and vegetation restoration.