Spatial distribution pattern of tree individuals in the Schrenk spruce forest, northwest China
天山云杉种群空间格局与动态

The spatial dispersion pattern of individual trees in forest communities is one of the central topics in community ecology. The Schrenk spruce (Picea schrenkiana) forest is the most widely spreaded forest type in Xingjiang Province, northwest China. It has profound significance in soil and water conservation, timber harvesting, and climate regulation to the region. Understanding tree dispersion pattern is important to conserve and manage the forest sustainablly. Two sample plots in the Xingjiang Agriculture University's Experimental Forest, with the area of 2.52 hm~2 and 3.0 hm~2, were set up for field investigation. Species within each plot were identified, and number of species, tree height, tree age, and DBH (diameter at breast high) were recorded for each individual tree. The spatial distribution pattern of individual trees was further analyzed using the Ripley's K function. The results showed that Schrenk Spruce tree individuals distributed in an aggregative fashion. X~2 test showed that there was no significant deviation from the Poisson expectation to a distance of 10 m, but significant clumping pattern occurred beyond this distance, and it could reach 86 m. Two measures about the population distribution pattern, Ripley's K statistic and quadrat methods were compared and the result showed that the former was better. This suggested that random distribution at the local (nearest neighbor) scales gave way to the clumpy pattern at larger scales. Furthermore, dead Schrenk trees were significantly clumped at all scales. Two other common tree species in the Schrenk spruce forest, Betula tianschanica Rupr. and Salix tianschanica Rgl. were also distributed aggregatively, and the degree of aggregation is even higher than that of spruce trees. The aggregation of Betula and Salix is different in two sample plots because of the succession stage is different. The spatial distribution pattern of Schrenk Spruce was closely related to tree ages. The younger the trees, the more aggregative the distribution pattern tended to be. But the degree of aggregation of Spruce trees with ages larger than 150 years tended to be higher than any other age classes due to the forming of forest gaps. Individual tree distribution pattern could also be influenced by its regeneration characteristics and surrounding microenvironments. Further studies should be devoted to analyze the relationship between the spatial distribution pattern and these influencing factors.