陕北黄土区林分空间点格局分析

Spatial Point Pattern Analysis on Forest Stands in Loess Slope,Northern Shaanxi

林分空间分布格局对陕北黄土丘陵沟壑区近自然植被恢复具有重要意义.在陕北吴起县阴坡坡向选取约5.0hm2的林地测得山杏、小叶杨以及榆树等乔木树种的树高、胸径等指标.分析林分的树高与胸径分布特征,并采用空间点格局方法分析山杏、小叶杨、榆树等种群的空间分布格局以及种群间的空间关联性.结果表明:(1)山杏、小叶杨及榆树均以中树和大树为主,幼树较少;(2)山杏、小叶杨及榆树种群在0—100m空间尺度内均为聚集分布,但山杏种群在r=70m时达到最大聚集强度,小叶杨与榆树种群在r=40m时达到最大聚集强度;(3)山杏与小叶杨种群在0—20m空间尺度内关联性不显著,在20—100m内呈显著正关联性,榆树与山杏、小叶杨种群在0—100m空间尺度内均呈显著负关联性.因此,该区近自然造林时小叶杨可混交在山杏林隙内,且山杏造林规模的最大半径为70m,混交在林隙内的小叶杨造林规模的最大半径为40m.山杏与榆树不可混交.

Stand spatial pattern plays an important role in near-natural vegetation restoration in the hilly Loess Plateau of Northern Shaanxi. A shady slope （5hm2） in Wuqi County, Shaanxi Province was selected to measure the height and diameter at breast height （DBH） of all trees including Armeniaca sibirica, Populus simonii and Ulmus pumila grew on it. Spatial point pattern method was applied in analyzing their spatial pattern and spatial associations. The results showed that：（ 1 ）the middle-aged and mature individuals were dominant in these species with few young individuals ; （ 2 ） the populations of A. sibirica, P. simonii and U. pumila showed on clumping distribution at the scale of 0-100m respectively, while A. sibirica population reached the maximum clumped intensities at the scale of 70m, and individuals of P. simonii and U. pumila reached the maximum clumped intensities at the scale of 40m; （3） the spatial association between A. sibirica and P. simonii was not significant at the scale of 0--20m, but that was significant positive correlation at the scale of 20--loom. By contrast, the spatial association among A. sibirica and U. pumila and P. simonii and U. pumila were significant negative correlation at the scale of 0--loom. These findings indicted that A. sibirica could mix with P. simonii, and the maximum radiuses of forestation scale of A. sibirica and P. simonii were 70m and 40m respectively, but A. sibirica should not mix with U. pumil.