Niche characteristics of herb populations within three forest types in hilly red soil region of southern China

The niche theory has been successfully used to explain competition mechanisms among the coexisting species in natural communities, which is significant for understanding of the coupling between plant community construction and environmental factors. The niche characteristics of herb populations were examined within coniferous forest(CF), broad-leaved forest(BF) and mixed broadleaf conifer forest(MF) in hilly red soil region of southern China, using Levins niche breadth, Pianka index of niche overlap and niche similarity formula, from the perspective of the growth status in different forest communities in herbage species. Results showed, the mean niche breadth of all herbage species in the studied forest communities was in order CF(0.572)>MF(0.508)>BF(0.424). The niche breadth of Tetrastigma formosanum, Lophatherum gracile, Dryopteris sp., Serissa japonica and other herbaceous plants in CF were higher than that in MF and BF. The niche overlap did not always correlate to niche breadth. Larger niche overlap or even completely overlapping might occurr between the species with narrow niche breadth. There was a significant positive correlation between the niche breadth and the important value of the main herbaceous plants in CF and BF(P<0.01),with the correlation coefficients of 0.758 and 0.918, respectively. There was a significant negative correlation between the niche breadth and the important value of the coefficient of variation of herbage species in three forest communities(P<0.01), with the correlation coefficients of -0.996, -0.967 and -0.963, respectively. Our study suggested the CF and MF were still in an instability state at present stage of community succession due to high niche overlap among herb populations and high spatial heterogeneity of environmental resources in study region.