Abstract:

Canopy gaps, created by the death or disturbance of a mature tree, influence forest community structure. The opening of the canopy creates opportunity for species recruitment influencing species diversity in forest communities. However, the mechanisms that lead to species recruitment and the resulting diversity are still unclear. Factors that may affect species richness of canopy gaps include the gap area, species richness of adjacent areas (SSAA and SCAA represent the adjacent area where is the seed source of canopy gap and the adjacent area where species composition is spatially correlated with survivors in the canopy gap, respectively), topography, and soil nutrients. To test which factors significantly affect species richness, 11 parameters (canopy gap area, species richness of mature individuals in SSAA, species richness of all individuals in SCAA, slope, aspect, convexity, mean elevation, pH value, total nitrogen, total carbon, total phosphorus of each gap) were calculated for 84 canopy gaps in 20 ha Tiantong Dynamics Plot. The effect of SSAA and SCAA were quantified by species richness of mature individuals and richness of all free standing trees (DBH ≥ 1 cm) within 5 m and 4 m away from the edge of the gap, respectively. The size of adjacent area was defined as the area containing most of species present in the gap (≥75%) and having most significant effect on gap species richness. A generalized linear regression model was constructed for each random combinations of any subsets of 11 gap parameters. Our best model with lowest AIC_c showed that: only species richness of mature individuals in SSAA and the canopy gap area had a significant effect on the gap species richness. This result suggests that gap size and species richness of the seed source can directly influence species richness of canopy gaps. Additional factors may have an indirect influence and should be explored further.

Key words: gap size, species diversity, seed source, canopy gap area, Tiantong, forest community, dynamics plot