Abstract:

Aims Many mechanisms of forest patterns have been examined in tropical rain forest; however, there are only a handful of similar studies on subtropical broad-leaved evergreen forest. Our objective is to analyze the main mechanisms of distribution pattern of Castanopsis eyrei and Schima superba in GTS (Gutianshan) forest plot.

Methods Based on a stem map of a 24 hm² permanent plot in the middle subtropical broad-leaved evergreen forest at Gutianshan National Reserve, we analyzed the distribution pattern of the dominant species C. eyrei and S. superba in saplings, juvenile trees, adult trees, large trees and old trees using spatial point pattern analysis. We also examined spatial associations among different growth stages.

Important findings Castanopsis eyrei and S. superba had a clustered distribution across a range of scales (0-100 m). Saplings, juvenile trees and adult trees tended to be more clumped than big trees. Old trees tended to be somewhat more clumped than big trees. Our results suggested that the two species have obvious habitat preferences at larger scales. For C. eyrei, saplings were significantly positively associated with juvenile trees at scales ≤ 100 m, as were saplings and adult trees, juvenile trees and adult trees, adult trees and big trees. Generally there was no correlation between big trees and old trees at scales ≤ 10 m, whereas their association tended to be positive at larger scales (10-100 m). Generally there were negative or no correlations between other size classes. For S. superba, the saplings were significantly positively associated with juvenile trees at scales ≤ 100 m, as were saplings and adult trees, juvenile trees and adult trees. Generally there were negative or no correlations between juvenile trees and old trees, adult trees and old trees, big trees and old trees, saplings and big trees, juvenile trees and big trees, adult trees and big trees. Generally there was negative correlation between saplings and old trees at scales ≤ 20 m, whereas their association tended to be positively at larger scales (25-100 m). These results suggested that dominant species facilitated coexistence of other species through emptying space for colonization of other species, which is probably attributed to density dependence or the Janzen-Connell effect. Both processes depended on species in intensity and acting time.

Key words: GTS (Gutianshan) forest plot, mid-subtropical-broad-leaved evergreen forest, point pattern analysis, spatial association, spatial distribution patterns