Castanopsis Fargesii Decline And The Effect On Seedling Recruitment On Mt. Jinyun

Forest decline is a widely concerned ecological issue. Castanopsis fargesii, a dominant species of the evergreen broad-leaved forest in Mt. Jinyun, declined severely since 2008. This has brought great threats to the ecological security of Jinyun National Nature Reserve and Chongqing metropolitan area. In this study, species composition and structure of C. fargesii communities, as well as the decline of C. fargesii, the regeneration of C. fargesii community and the impacts of forest gap after C. fargesii decline on seedling recruitment, were investigated in a 0.5 hm2 long-term monitoring plot. Major findings were summarized as follow:①A total of 69 species of vascular plants, belonging to 32 families and 48 genera, was recorded within the 0.5 hm2 plot. Within the 69 species, 59 were evergreen broad-leaved trees, with 7 species being deciduous trees and 3 species being conifers. The dominance of the evergreen broad-leaved trees are over 91%. C. fargesii, Machilus pingii and Symplocos setchuanensis were also the dominant species in the C. fargesii community. The Relative Basal Area(RBA) of C. fargesii accounted for 48.3%.②C. fargesii decline is a normal phenomenon on Mt. Jinyun, and the decline was related to tree height and diameter at breast height(DBH). C. fargesii decline occurred only for the large individuals(H>8m, DBH>10cm). 49 individuals out of 58, accounting for 84.5% showed levels of decline. Declined individuals showed a random spatial distribution at the 0~20m scale. However, at the 20~25m scale, declined individuals showed an aggregated spatial distribution.③A total of 2944 seedlings was recorded within the study plot. The spatial distribution of seedlings was aggregate at the 0~15m scale, and random at the 15~16m scale, and uniform at the 16~25m scale.④C. fargesii decline created forest gaps and caused significant changes of understory light environment. The growth of C. fargesii seedlings has a significant positive correlation with light intensity and soil humidity. The height growth of seedlings older than 6 years differed significantly when grown under forest gap and under canopy. Similarly, the height growth of seedlings older than 10 years showed ever larger differences.⑤The distribution of C. fargesii DBH class showed an inverse-J type, suggesting that C. fargesii community regenerates continuously. But in recent 5 years, the number of C. fargesii seedlings has decreased, pointing to potential crisis for the recruitment of C. fargesii.