Negative density dependence (NDD) has been recognized as a driving mechanism that may underpin the maintenance of tree species diversity in tropical forests. Density-dependent survival tends to be prevalent among species at the seedling stage and is recognized as a potentially important mechanism for maintaining tree species diversity. However, there is little knowledge of how density dependence changes in fluctuating environments.
Dr. Lin Luxiang and his teachers of Xishuangbanna Tropical Botanical Garden (XTBG) conducted a study to examine temporal variations in the effects of local conspecific and heterospecific neighbours on seedling survival in the 20-ha Xishuangbanna tropical seasonal rain forest dynamics plot located in Mengla County, Yunnan province, southwest China (101°34′E, 21°36′N).
Using data on the survival of 7263 seedlings of 186 species in the 20-ha plot, the researchers tested for seasonal differentiation in density dependence and test whether local-scale negative density dependence was related to community-level species abundance.
The research results suggest that local-scale negative density dependence tends to be stronger in the dry than wet season in the Xishuangbanna tropical forest. The study provides further evidence that the density and identity of neighbouring individuals influence juvenile survival at both local and larger spatial scales in forest communities, and lends support to the idea that NDD influences the diversity and abundances of tropical tree species.
In addition, their results highlight the fact that simple models of negative density dependence, in which the strength of conspecific neighbour effects is consistent over time and across species, do not capture the variation observed in real-world communities.
The study was funded by the National Natural Science Foundation of China (31000201) and the National Science & Technology Pillar Program from the Ministry of Environmental Protection of China (2008BAC39B02).
The work entitled “Seasonal differentiation in density-dependent seedling survival in a tropical rain forest” has been published online in Journal of Ecology, DOI:10.1111/j.1365-2745.2012.01964.x