Abstract
The objective of this study was to infer the most important gradients influencing species composition and abundance of colonizing native trees (CNT) in an unthinned Japanese cedar (Cryptomeria japonica D. Don) plantation in northern Japan. A 0.84-ha (60×140m) plot was established in the stand and was subdivided into a total of 42 subplots (20×10m each). For each tree >3cm in diameter at breast height (DBH) in each subplot, we recorded the species and DBH. Path analysis with structural equation modeling was performed to analyze the correlation and causal relationships between slope characteristics, soil properties and vegetation attributes of the set of subplots. Species composition of CNT was strongly affected by site conditions along relatively short gradients of slope aspect and soil water content, but stand height had little effect on species composition. In contrast, the abundance of CNT was strongly affected by site conditions along relatively short gradients of slope aspect and soil water content, and stand height also significantly affected abundance. The contrasting patterns of variation between species composition and abundance of the CNT may reflect the fact that the mortality rate of CNT at the adult tree stage varies according to vertical stand structure rather than to interspecific differences in survival patterns. In conclusion, recruitment patterns from the juvenile tree stage for each species were related principally to species composition and abundance of CNT, and site-specific mortality at the adult stage was also significantly related to the abundance of CNT.
