间伐对华北落叶松林林分结构稳定性的影响

为研究间伐对华北落叶松林分结构稳定性的影响，使得森林结构分布更加合理，对关帝山林区的华北落叶松采取不同抚育强度的间伐，测定林分内物种丰富度和生长指标，依托胸径计算不同间伐样地的角尺度、混交度和大小比数，分析间伐对林分物种结构和空间结构参数的影响，综合评价森林结构的稳定性。结果表明，随着间伐强度的增加，林分物种多样性各参数无明显变化规律，但当强度大于17%时整体物种多样性优于对照样地，角尺度呈先下降后上升再下降的趋势，混交度呈先上升趋于稳定后下降的趋势，大小比增加并趋于稳定。由此可知，17%以上的间伐强度能够改善林分整体物种结构，13%~17%的间伐强度适用于调整华北落叶松林分分布状态，间伐对于改善林分内树种组成结构具有积极促进作用，间伐使得林分内树木竞争减弱。

Effects of Thinning on the Stand Structure Stability of Larix principis-rupprechtii Forest

In order to study the effect of thinning on the stand structure of Larix principis-rupprechtii to make the distribution of forest structure more reasonable,thinning management with different intensities was conducted in the L.principis-rupprechtii forest occurring in Guandi Mountain.The diameter at breast height (DBH) of the trees and species richness in the stand were measured.The angle scale,mixing degree and size ratio of different thinning plots were calculated based on DBH.The influences of thinning on the structures of the stand specie and spatial structure parameters were analyzed.The stability of the forest structure was comprehensively evaluated.The results showed that with the increase of thinning intensity,there was no obvious change rule in the parameters of species diversity,but when the intensity exceeded 17%,the overall species diversity was better than the control plot; the angle scale decreased at first,increased and then decreased; the mingling degree increased at first,tended to be stable and then decreased; and the size ratio increased and tended to be stable.It can be concluded that over 17% thinning intensity can improve the overall species structure of the stand.Thinning intensities of 13%-17% are suitable for adjusting the distribution of L.principis-rupprechtii forest.Thinning can improve the composition of tree species in the forest,and make the competition of trees in the stand weaken.