西藏色季拉山急尖长苞冷杉原始林粗木质残体空间格局分析

Spatial distribution patterns of coarse woody debris in the Abies georgei var. smithii pristine forest in the Sejila Mountain

粗木质残体(Coarse woody debris,CWD)的空间格局反映了森林群落的死亡格局和干扰格局,在一定程度上体现了群落内林木的死亡过程。采用相邻网格法对色季拉山急尖长苞冷杉(Abies georgei var.smithii)原始林1 hm^2固定样地内CWD进行调查,从CWD类型、腐烂等级、径级3个方面对CWD空间分布格局进行分析。结果表明:样地内CWD总密度为582株/hm^2,倒木占55.33%,是CWD的主要输入形式。CWD密度在腐烂等级上的分布可用多项式拟合(R^2=0.9973),在径级上的分布可用指数衰减模型拟合(R^2=0.9746),且在不同类型、腐烂等级及径级上的分布差异较大。在50 m尺度内,CWD整体表现为小尺度的集群分布和中、大尺度的随机分布。在3种CWD分类中,仅有大枯枝、Ⅰ级腐烂、径级ⅠCWD在小尺度或中尺度表现为较强的集群分布,其余则均以随机分布为主,只是在个别尺度达到或接近集群分布。不同类型CWD间整体关联不显著,只有枯立木与大枯枝在0—21 m尺度内达到显著负关联。CWD空间分布格局是急尖长苞冷杉原始林的重要结构特征,在很大程度上决定着林下植物群落及林型自然更新格局。

The spatial pattern of coarse woody debris(CWD)reflects the death and disturbance patterns of forest communities,and to some extent,the death of forest trees.The adjacent grid method was used to investigate the CWD,in a 1 hm^2 fixed plot,of the original Abies georgei var.smithii forest in the Sejila Mountain and analyze the spatial distribution of CWD from three perspectives:CWD type,decay grade,and diameter grade.The results showed that the total density of CWD in the plot was 582 plantshm^2,among which the inverted wood,the main form of CWD,accounted for 55.33%.The distribution of CWD density at the decay level can be fitted by a polynomial(R^2=0.9973),while the distribution at the diameter level can be fitted by an exponential decay model(R^2=0.9746),which is greatly affected by its types,decay grades,and diameter classes.Over a 50 m area,the overall performance of CWD displays a cluster distribution at a small scale and random distribution at medium and large scales.Among the three CWD classifications,only the large dead branches,the first grade decay,and the diameter level I CWD displayed a strong cluster distribution at a small scale or mesoscale and the rest were basically distributed randomly,but only reached or approached the cluster distribution at individual scales.The overall correlation between different types of CWD was not significant,and only the dead standing trees and large dead branches reached a significant negative correlation over a 0—21 m scale.The spatial distribution pattern of CWD is an important structural feature of the primitive forest of Abies georgei var.smithii,which largely determines the natural regeneration pattern of understory plant communities and forest types.