The spatial pattern and canopy-understory association of trees in a cool temperate, mixed forest in western Japan

The spatial distribution pattern of trees and the association between canopy and understory individuals were examined with reference to the distribution of tree crowns in a cool temperate, mixed forest in Ohdaigahara, western Japan. Line transect and contact sampling methods were used to examine the pattern over various spatial scales. These methods are useful to detect patterns over a large study area. The dominance of Chamaecyparis obtusa on steep slopes forming large patches suggested that the distribution of this species is a consequence of landslides. Understory Fagus crenata showed a dumped distribution, and the relative coverage of this species was larger in canopy gaps than under a closed canopy. Understory individuals of Abies homolepis showed a positive association with canopy trees of F. crenata but a negative association with conspecific canopy individuals. These patterns suggested that F. crenata regenerates in canopy gaps and is replaced by A. homolepis. The dynamics of these two species are consistent with the process of gap dynamics. The effects of both small- and large-scale disturbance must be evaluated to understand the mechanisms of patch formation and the coexistence of forest tree species.