Understanding the spatial distribution of species diversity is one of the central issues in community ecology. Environmental conditions, dispersal limitation, and disturbance have been suggested to be important processes influencing spatial patterns in species diversity. At local scales, however, species distribution and habitat factors always show comparable spatial aggregation, making it difficult to understand how different processes regulate the spatial distribution of diversity and species composition. 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. Spatial analysis method of principal coordinates of neighbor matrices was used to disentangle the contributions of these processes at different spatial scales. And canonical correspondence analysis was conducted to know the relationship between pioneer vs. non-pioneer saplings and environmental variables.
Results/Conclusions
The results suggested that: (1) fine-scale spatial patterns are more important for pioneer than for non-pioneer species; (2) dispersal limitation showed stronger effects on non-pioneer saplings than pioneer saplings; and (3) soil chemistry explained the greatest variations for both two functional groups, followed by disturbance for the pioneer group, topography for the non-pioneer group, and then soil texture and moisture content. Results of canonical correspondence analysis indicated that species distributions were significantly correlated with topographic, soil and disturbance variables. It was also evident that plant species, geomorphic processes, and disturbance have different effects on the physical and chemical properties of soils.
Overall, we inferred that environmental control was the main process that regulates spatial distribution of species diversity for both pioneer and non-pioneer saplings. Disturbance effects contributed to fine-scale spatial variations for pioneer saplings, whereas topographic and soil effects contributed to broad scale spatial variations for non-pioneer saplings. Concurrently, dispersal limitation was also an important process influencing spatial distribution of species diversity for both functional saplings, especially non-pioneer saplings. Results also emphasized the role of the disturbance process in maintenance of pioneer species composition, which simultaneously structured plant diversity. Although species distributions were significantly correlated with topography, soil and disturbance, we concluded that both topographic factors and plant species could also exert strong control over soil chemical and physical properties, thus influencing vegetation-soil patterning.