Dynamics of an old evergreen coppice in southwestern Japan with special focus on a typical coppice species (Castanopsis cuspidata) and a climax species (Distylium racemosum)

摘要

We investigated stand dynamics of an abandoned evergreen coppice (c.a. 100 years old) over the course of 21 years in south Kyushu, Japan. The study stand showed a change in species composition from being dominated by Castanopsis cuspidata to Distylium racemosum, that is, from a typical coppice species to a typical climax species of the region. However, the relative dominance of Castanopsis spp. appeared to remain very high in the study stand compared to that in the Aya Research Site, a typical old-growth forest in the region, due to abundant C. cuspidata canopy trees of coppice origin. This suggests that the species composition of the study stand remained distinct from that of climax forests in the region. On the other hand, D. racemosum did not show a significant change in diameter at breast height (DBH) class frequency distribution from 1996 to 2017, probably due to the slow growth of this species. However, generalized linear models (GLMs) were used to identify the factors affecting better DBH growth of this species in the gap, indicating the potential for further development of the population structure when small trees are released from suppression of canopy trees. This suggests, inversely, that the development of the D. racemosum population was heavily suppressed by abundant C. cuspidata canopy trees of coppice origin that survived to the age of nearly 100 years. Further, large typhoons are suggested to cause severe canopy disturbances that remove canopy trees of C. cuspidata, which might be important for promoting further forest succession, even for a nearly 100-year-old evergreen old coppice.