庐山常绿阔叶林不同生长阶段林木空间结构特征及其评价

Spatial structure characteristics and its evaluation of evergreen broadleaved forest at different growth stages in Lushan Mountain, Jiangxi Province of eastern China

【目的】分析林木不同生长阶段的空间结构特征有利于认识林分更新及其稳定性,为优化林分空间结构及自然植被恢复等提供参考依据。【方法】以庐山常绿阔叶林为研究对象,将林木生长划分为幼树(1 cm≤DBH <5 cm)、小树(5 cm≤DBH <10 cm)、中树(10 cm≤DBH <20 cm)和大树(DBH≥20 cm)4个阶段,选用混交度、大小比数、密集度、角尺度4种空间结构参数构建空间结构综合指数,采用熵权法进行权重赋值。【结果】(1)幼树、小树、中树、大树的株数占林分总株数的比例分别为72.7%、16.8%、6.5%和4.0%,林分径级结构整体上呈倒“J”型。(2)幼树、小树、中树、大树的平均混交度分别为0.609、0.746、0.815和0.822,平均大小比数分别为0.545、0.268、0.132和0.089,平均密集度分别为0.852、0.895、0.871和0.842,平均角尺度分别为0.576、0.563、0.553和0.507;随着径级的增大,林木的混交、生长优势程度不断增大,密集程度先增大后减小,分布格局逐渐由聚集分布转变为随机分布。(3)小树、中树、大树的大小比数的权重均超过75.0%,优化其空间结构主要应调控其林木分化程度;幼树混交度和大小比数的权重分别为0.364和0.388,优化其空间结构则主要调控林木混交程度及分化程度。空间结构综合指数为大树(0.054)<中树(0.082)<小树(0.117)<幼树(0.265)。【结论】庐山常绿阔叶林中林木随着径级的增大其空间结构逐步得到改善,大树的空间结构最好,幼树的空间结构最差;针对不同生长阶段林木空间结构特征,可以采取不同的经营措施以优化其空间结构。

[Objective]The analysis of stand spatial structure at different growth stages is conductive to understanding stand regeneration and stability,which can provide reference for optimizing stand spatial structure and natural vegetation restoration.[Method]In the study,the evergreen broadleaved forest in Lushan Mountain,Jiangxi Province of eastern China was taken as the research object.The tree growth was divided into four stages:sapling(1 cm≤DBH<5 cm),small tree(5 cm≤DBH<10 cm),middle tree(10 cm≤DBH<20 cm)and large tree(DBH≥20 cm).The comprehensive index of spatial structure was constructed by four kinds of spatial structure parameters:mingling,neighborhood comparison,crowding degree and uniform angle index.The weight was assigned by entropy weight method.[Result](1)The proportions of sapling,small tree,medium tree and large tree were 72.7%,16.8%,6.5%and 4.0%,respectively.The diameter class structure of the stand was generally inverse‘J’type.(2)The average mingling of sapling,small tree,middle tree and large tree were 0.609,0.746,0.815 and 0.822,respectively.The average neighborhood comparison of them was 0.545,0.268,0.132 and 0.089,respectively.The average crowding degree of them was 0.852,0.895,0.871 and 0.842,respectively.The average uniform angle index of them was 0.576,0.563,0.553 and 0.507,respectively.With the increase of diameter class,the degree of mingling and growth dominance of trees increased,and the density of trees first increased and then decreased.The distribution pattern gradually changed from aggregation distribution to random distribution.(3)The weight of neighborhood comparison of small tree,medium tree and large tree was more than 75.0%.The way of optimizing spatial structure should mainly regulate the degree of forest differentiation.The weight of mingling and neighborhood comparison of sapling were 0.364 and 0.388,respectively.To optimize its spatial structure,the degree of forest mingling and differentiation should be mainly controlled simultaneously.The comprehensive index of spatial structure was large tree(0.054)<middle tree(0.082)<small tree(0.117)<sapling(0.265).[Conclusion]The spatial structure of evergreen broadleaved forest in Lushan Mountain was gradually improved with the increase of diameter class.The best spatial structure was the large tree and the worst was the sapling.According to the spatial structure characteristics of trees at different growth stages,different forest management measures can be taken to optimize the spatial structure.