杨桦次生林是冀北山地的典型森林类型，对区域生态环境建设与经济持续发展具有重要作用。研究以冀北黑龙山的杨桦次生林为例，利用角尺度、混交度及大小比数以及参数熵权修正层次分析法，对中龄林与幼龄林的结构及森林自然度进行比较分析。结果表明：幼龄林与中龄林的树种组成均较单一，中龄林的树种多样性指数较高，树种组成较好；中龄林的直径分布范围较大，林木个体分化程度明显；幼龄林与中龄林的树高结构均呈单峰型，幼龄林树高分布范围较小，林层分化不明显；幼龄林与中龄林的林分角尺度都呈聚集分布，但中龄林林木个体分布较趋于随机；中龄林与幼龄林均以零度混交比例为主，中龄林的林分整体混交度相对较好；幼龄林与中龄林林分大小比数分化差异不明显，林分不同大小比数分布频率较均匀。幼龄林森林自然度等级为4，属于乡土树种混交林状态，中龄林森林自然度等级为5，属于次生林状态。%Secondary poplar-birch forest is a typical forest type in mountain area of north Hebei, and plays an important role in ecological construction and economic development of the region. Secondary poplar-birch forest in Heilongshan, mountain area of north Hebei was studied, comparative analysis about structure and naturalness were conducted in the middle-aged forest and young forest, and three parame-ters-angle index, neighborhood comparison, mingling and entropy weight AHP-were used. The results show that the species composition of young forest and middle-aged forest were single, tree species diversity of middle-aged forest was higher, species composition was better;The diameter distribution range of middle-aged forest was larger, individual differentiation was obvious;The tree height structure of young forest and middle-aged forest both showed single peak type, the height distribution range of young forest was smaller, the layer differentiation was not obvious;The uniform angle index of young forest and middle-aged forest were aggregated distribution, but tree distribution of middle-aged forest was tended to random;The mingling degree of young forest and middle-aged forest were dominated by zero mixed proportion, the mingling degree of middle-aged forest was relatively well;The neighborhood comparison of young forest and middle-aged forest was not significant, the different size neighborhood comparison frequency of forest stands were uniform. The naturalness ratio of young forest and middle-aged forest were four and five, respectively belonged to native species mixed forest and secondary forest.
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