Evidence has shown that saplings are more spatially aggregated than adults. This often results from dispersal limitation (neutral process) and habitat association (niche process). Understanding the mechanisms that maintain biodiversity in communities critically depends on our ability to decompose the variation of diversity into the contributions of different processes affecting it. In this study, we simplified the floristic complexity into two functional groups, and related to collected topography, soil, and disturbance variables in a 25-ha stem-mapping plot of the Lienhuachih subtropical evergreen broad-leaved forest in Central Taiwan. The coordinates of neighbor matrices (PCNM) method was used to disentangle the contributions of the effects of pure environmental, pure spatial, and spatially structured environmental processes on the distribution of richness, abundance and species composition of pioneer and non-pioneer saplings.
Results/Conclusions
Results showed that (1) the environment and space jointly explained 49.98%, 49.07% and 12.56% of the variation in richness, abundance and species composition for pioneer saplings, and 65.83%, 65.87% and 32.87% of that for non-pioneer saplings; (2) the richness and abundance of pioneer saplings were dominantly controlled by pure spatial effect (30.95%, 30.74%), secondarily controlled by spatially structured environment effect (18.00%, 16.95%); the richness and abundance of non-pioneer saplings were dominantly controlled by SSE effect (33.09%, 35.55%), secondarily controlled by PS effect (30.76%, 29.01%), and then pure environment effect (1.99%, 1.31%); the species composition of pioneer and non-pioneer ones were dominantly controlled by spatially structured environment effect (5.45%, 21.87%), secondarily controlled by pure spatial effect (4.19%, 7.95%), and then pure environment effect (1.93%, 2.05%); (3) variation partitioning of environmental variables: disturbance variable of the richness and abundance of pioneer saplings explained the most environmental variations than soil and topographic variables. Topographic variables explained the most environmental variations than other two variables for non-pioneer saplings. But soil variables explained the most environmental variations of species composition of both two functional groups. (4) broad-scaled spatial variation dominated the spatial distribution of diversity of both pioneer and non-pioneer saplings, and fine-scaled spatial variation showed stronger effect on pioneer saplings than non-pioneer ones. In a rough terrain and frequently disturbed forest, dispersal limitation (spatial) is important for the richness and abundance of both two groups. In terms of the environmental control, disturbance effect dominated the richness and abundance of pioneer saplings, topography effect dominated the richness and abundance of non-pioneer ones, but soil effect dominated the species composition of both two functional groups.