江西九连山亚热带常绿阔叶林优势种空间分布格局

Abstract

Population structure and spatial pattern are important characteristics of plant community which can reveal ecological characteristics of a species.Numerous mechanisms of population distribution pattern have been examined in tropical rain forests,however,there are only a handful of similar studies conducted in a subtropical evergreen broad-leaved forest.In this study,a plot covering 4 hm2(200 m×200 m) was established in a subtropical evergreen broad-leaved forest in the Jiulian Mountain National Nature Reserve.All trees with a diameter at breast height of at least 1 cm were mapped and the species identified.Point pattern analysis was applied to analyze the influence of environmental heterogeneity on tree spatial distribution.The focus is on four dominant species: Castanopsis lamontii,C.carlesii,Diospyros morrisiana and Eurya loquaiana at different growth stages(saplings,juvenile and mature trees).Using the univariate O-ring statistic,we explored the differences of the population patterns with or without considering environmental heterogeneity.Additionally,the bivariate O-ring statistic was also used to examine spatial associations at different growth stages for each dominant species.The results show that environmental heterogeneity significantly affects tree spatial distributions,most trees showing significant aggregated in the plot.All the four dominant species presented obvious habitat preferences at larger scales.When using the null model of complete spatial randomness(CSR) without environmental heterogeneity effects,the dominant species were almost aggregated across all studied scales(0—30 m).However,the degree of aggregation distribution become weaker with increasing tree diameter.However,aggregation was only evident at short-distances if the environmental heterogeneity effect was eliminated by the null model of a heterogeneous Poisson process(HP).Saplings and juvenile trees showed a significant positive association at all scales from 0 to 30 m for each dominant species.For C.lamontii,there was a negative correlation between mature trees and saplings at scales of 3—4 m.Their association tended to show no correlation at smaller or larger scales(1—3 m,6—30 m).The association of juvenile trees and adult trees showed a similar tendency.There was almost no correlation between saplings and mature trees for C.carlesii.Similarly,mature trees and juvenile trees also showed no correlation at scales≤4 m while their association tended to be positive at larger scales of 5—30 m.D.morrisiana,saplings were significantly and positively associated with juvenile trees at scales≤30 m,as were juvenile trees and mature trees.Generally there was a negative correlation between saplings and mature trees at scales≤1m,but their association tended to show no correlation at scales of 1—5 m and presented a positive correlation at scales of 6—21 m and 26—30 m.Regarding E.loquaiana,a significantly positive correlation was found among different growth stages at scales≤30 m.Dominant tree species facilitated coexistence of other species through emptying space for colonization,which is probably attributed to density dependence or the Janzen-Connell effect,however,coexisting dominant shrub species did not show these effects.