天山云杉种群空间格局与动态

Spatial distribution pattern of tree individuals in the Schrenk spruce forest, northwest China

天山云杉(Picea schrenkiana)林是天山林区的重要针叶林。研究调查了两块分别代表天山云杉不同演替阶段的标准地,应用Ripley's K系数法研究了天山云杉种群空间格局与动态。结果表明:天山云杉是聚集型种群,天山云杉活立木、枯死木、天山桦(Betula tianschanica Rupr.)和天山柳(Salix tianschanica Rgl.)的空间格局均为聚集型;天山云杉枯死木的聚集强度大于天山云杉活立木的聚集强度;天山桦和天山柳的聚集强度大于天山云杉枯死木的聚集强度;天山桦和天山柳的空间格局随种群所处的演替阶段不同而不同,增长型种群在所有尺度上其空间格局都为聚集型,在大于70 m尺度上表现为均匀格局,而天山云杉成熟林中的天山桦和天山柳只在小尺度(0～4 0 m)上表现为聚集。随着天山云杉的生长,其聚集强度逐渐减小,聚集半径不断增大。从5 0 a以下天山云杉到5 0～10 0 a的天山云杉其聚集强度急速减小,这有利于天山云杉幼树获得足够的资源,是天山云杉幼树的一种生存策略或适应机制。15 0 a以上天山云杉的聚集强度增加,这是由于天山云杉生长到15 0 a左右时开始出现成熟后死亡,形成林窗有利于天山云杉林的更新。研究还对Ripley's K系数法和频次检验法进行了比较,Ripley's K系数法能够分析各种尺度下的种群空间格局,且不受样方大小?

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.