辽东山区次生蒙古栎成熟林空间结构及个体竞争特征

Spatial structure and individual competition characteristics of secondary Mongolian oak mature forests in the mountainous area of eastern Liaoning Province,China

天然成熟林的群落结构是森林长期演替的结果,具有合理的结构、丰富的生物多样性和较高的生态功能。揭示成熟林的空间结构及其形成机制是科学开展森林经营活动的基本前提。本研究基于林分的径阶结构、角尺度、大小比数、混交度4个结构参数和Hegyi单木竞争指数,分析了辽东山区次生蒙古栎成熟林的结构特征和竞争关系。结果表明:在乔木层蒙古栎占显著优势;在演替层蒙古栎、紫椴和色木槭占优势;在更新层则以假色槭、紫椴和色木槭为主,蒙古栎更新幼苗极少。林分整体径级分布呈倒“J”型,优势树种蒙古栎的径级结构呈正态分布;林分水平空间结构整体呈随机分布,以蒙古栎为对象木的平均角尺度为0.505,大小比数为0.219,混交度为0.670。从空间结构二元分布看,随机分布的蒙古栎个体较其他分布类型具有更大的生长优势和较高的混交度,随机分布的优势、亚优势个体占林分全部个体的近一半,与周边的树木个体具有高度的混交;林分单木竞争指数随径级的增大而减小,当胸径达到20 cm以上时竞争指数趋于稳定(ΔCI<2)。蒙古栎单木邻域竞争半径为8 m,且竞争压力主要来源于种内,非蒙古栎个体所受竞争压力则主要来源于种间。本研究揭示了群落个体竞争对次生蒙古栎成熟林空间结构形成的重要作用。

The community structure of natural mature forests is determined by long-term forest succession,charac-terized by rational structure,rich biodiversity,and high ecological function.Understanding the spatial structure and formation mechanisms of mature forests is a fundamental prerequisite for forest management.We analyzed four struc-ture parameters,including diameter structure,angular scale,size ratio,and mixture degree,as well as the Hegyi competition index,of secondary Quercus mongolica(Mongolian oak)mature forests in the mountainous area of east-ern Liaoning Province.The results showed that Q.mongolica predominated the tree layer.In the sapling layer,Q.mongolica,Tilia amurensis,and Acer pictum were the dominant species.In the seedling layer,Acer pseudosieboldia-num,T.amurensis,and A.amurensis dominated,with very few Q.mongolica seedlings.The overall diameter distri-bution of the stand showed an inverse“J”shape,while the diameter distribution of Q.mongolica,the dominant tree species,followed a normal distribution.The horizontal spatial structure of the stand was generally randomly dis-tributed,with an average angle scale of 0.505,size ratio of 0.219,and mixture degree of 0.670 for Q.mongolica.From the perspective of spatial structure binary distribution,Q.mongolica individuals which had a random distribu-tion exhibited greater growth advantages and higher levels of mixing,in comparison to other distribution types.Randomly distributed dominant and subdominant individuals made up nearly half individuals in the stand,and showed a high degree of mixing with surrounding trees.The stand-level individual tree competition index decreased with in-creasing diameter classes.When the diameter at breast height exceeded 20 cm,the competition index tended to sta-bilize(ΔCI<2).The competitive radius of individual Q.mongolica trees was 8 m,with intraspecific competition as the main pressure.Other species experienced competition pressure primarily from interspecific sources.Our results suggested that competition played an important role in shaping the spatial structure of secondary Q.mongolica ma-ture forests.