南盘江流域次生林中枯倒木的数量和结构特征

Quantitative and structural characteristics of fallen woods in a secondary forest in Nanpan River basin

枯倒木是森林演替过程中的必然产物,在维持森林生态系统的稳定、平衡和生物多样性中扮演重要角色。其形成原因和分解过程已有不少研究,但很少涉及数量和结构。本研究在中国西南地区南盘江流域的松栎混交林中建立3块面积分别为80 m×80 m、100 m×60 m和80 m×70 m的固定样地,依据现存状况将枯倒木分为DCs-Ⅰ、DCs-Ⅱ、DCs-Ⅲ、DCs-Ⅳ和DCs-Ⅴ5个分解等级,统计了每个分解等级的物种丰富度、株数和蓄积,并用林分空间结构参数(角尺度,uniform angle index,W;混交度,mingling,M;大小比数,domi-nance,U)分析它们的空间结构特征。结果表明:乔木的丰富度高,但株数少,对蓄积量的贡献大。灌木的丰富度低,但株数多,对蓄积量的贡献少;随着分解等级的增加,枯倒木的株数和蓄积呈增加或先增后减的趋势。种间的分解状况差异很大;枯倒木以中小径阶个体为主,大径阶个体较少;枯倒木的大小分化均衡(U=0.49~0.50),整体处于中低度混交(M=0.38~0.62)和轻微聚集(W=0.55~0.58)状态;随着分解等级的增加,枯倒木大小分化加剧。这些结果展示了南盘江流域次生林中枯倒木的组分、数量和空间结构特征,并暗示其分解程度与树种、个体大小以及空间属性相关,为粗木质残体的科学管理提供依据。

Fallen wood is an inevitable product during forest succession,which plays an important role in maintaining the stability,balance,and biodiversity of forest ecosystems.Many studies have explored the formation and decomposition process of fallen woods,but few referred to their quantity and structure.In this study,we investigated fallen woods in three plots with an area of 80 m×80 m,100 m×60 m and 80 m×70 m in a pine-oak mixed forest in the Nanpan River basin,Southwest China,.Fallen woods were divided into five grades(DCs-Ⅰ,DCs-Ⅱ,DCs-Ⅲ,DCs-Ⅳand DCs-Ⅴ)according to their decay statuses.Species richness,abundance,and volume were estimated and the characteristics of spatial structure were analyzed with the stand spatial structure parameters(i.e.,uniform angle index,W;mingling,M;Dominance,U).Trees had many species,but with few individuals,which greatly contributed to volume.Shrubs had many individuals belonging to a few species,and accounted for a small part of volume.The abundance and volume of fallen woods increased directly or first increased and then decreased with increasing decay grades.Species markedly differed from each other in decay.Middle and small-sized woods constituted the main body of fallen woods,and large-sized ones accounted for a small amount.On the whole,fallen woods were at a state of mediumlow mixing(M=0.38-0.62)and slight aggregation(W=0.55-0.58),and had a balance of size differentiation(U=0.49-0.50).With the increases of decay grades,the size differentiation of fallen woods became large.These results clearly demonstrated the characteristics of species composition,quantity and spatial structure of fallen woods in a secondary forest in the Nanpan River basin,and indicated that the decay of fallen woods was closely related to species identity,their quantitative and spatial attributes,providing a basis for the scientific management of coarse woody debris.