杉木生态公益林林分空间结构分析及评价

Analysis and Evaluation of the Stand Spatial Structure of Cunninghamia lanceolata Ecological Forest

【目的】分析杉木生态公益林林分空间结构并对其进行评价,为杉木生态公益林空间结构优化措施的制定和其他生态公益林纯林空间结构优化调整措施的制定奠定理论基础。【方法】基于福寿林场不同龄组杉木生态公益林（幼龄林、中龄林、近熟林）18个固定样地的实测数据和9个固定样地的复测数据,采用Voronoi图确定林木的空间结构单元,进而用混交度、大小比数、角尺度、竞争指数、林层指数和开敞度6个林分空间结构参数分析3个龄组杉木生态公益林间伐补植前后的林分空间结构特征,采用乘除法对各个空间结构参数进行多目标规划,提出林分空间结构评价指数,并参考人工林近自然化改造的目标和技术指标,采用定性和定量相结合的方法,将林分空间结构评价指数值划分为5个评价等级。【结果】3个龄组杉木生态公益林间伐补植前的混交度和林层指数都偏低,林分混交程度低,稳定性差,垂直空间结构较差,林木对垂直方向的空间利用不足;大小比数都接近中庸状态,林木个体差异不大,林木分化不严重;角尺度为均匀分布和随机分布的中间状态,不是理想的水平分布格局;幼龄林开敞度较大,林木生长空间充足,中龄林和近熟林开敞度较小,林木生长空间不足;随着杉木的生长发育,竞争指数呈现出逐渐增加的趋势,说明杉木年龄的增加使林木个体所承受的竞争压力越来越大。18个固定样地杉木生态公益林林分空间结构评价指数为0.185 9~0.364 7,评价等级属于1级的样地占样地总数的11%,属于2级的样地占样地总数的89%,分属3,4,5级的样地没有,这说明杉木生态公益林的空间结构距理想状态差距还很大,需要进行林分空间结构优化。间伐补植后3个龄组杉木生态公益林的林层指数和混交度得到明显提高,林木个体差异变大,中、幼龄林的生长空间更加充足,9个复测样地杉木生态公益林林分空间结构评价指数为0.346 2~0.613 1,评价等级属于2级的样地占样地总数的11%,属于3级的样地占样地总数的78%,属于4级的样地占样地总数的11%,这说明通过间伐补植林分空间结构得到了明显改善。【结论】分析林分空间结构,能够发现林分空间结构中存在的不合理性,从而为优化空间结构经营措施提供依据。林分空间结构评价指数的提出可为杉木生态公益林的理想空间结构及其表达探索一条新途径,可为改造以杉木为主的人工生态公益林向理想结构演变提供理论依据,从对研究区杉木生态公益林林分空间结构的评价结果来看,可较客观地反映杉木生态公益林间伐补植前后林分空间结构的实际现状。

【Objective】The aim of this study is to provide the theoretical basis for optimizing the stand spatial structure and for developing its ecological,economic and cultural functions by analyzing and evaluating the stand spatial structure of Cunninghamia lanceolata ecological forest. 【Method 】 Neighbor trees of the object one was determined based on the Voronoi diagram,and Stand spatial structure index was calculated based on the measured data in eighteen permanent sample plots and the retest data in nine permanent sample plots of Cunninghamia lanceolata ecological forest of different age groups（ young,half-mature and near mature） in Fushou Forest Farm of Hunan province. Mingling index,neighborhood comparison,uniform angle index,competition index,stand layer index and open degree of stand were selected to analyze their spatial structure characteristics before and after thinning and replanting. Meanwhile,adopted multiplication divisionmethod making a multi-objective programming for each spatial structure parameter,the evaluation index of stand spatial structure was put forward. Making reference to target and technical index of near-natural transformation of plantation and using the integration of qualitative and quantitative methods,the evaluation index values of stand spatial structure were divided into five grades.【Result】Before thinning and replanting,stand layer index and mingling index was generally low,indicating that mingling degree of tree species was low,the stability of the stand vertical space structure was weak,and the use of vertical space of trees was underutilized. Also,neighborhood comparison of DBH of the stands was closed to moderate state,the numbers of trees in diameter classes were distributed uniformly,and there was minor difference between individual trees,uniform angle index of the stands was belonging to the intermediate state of uniform and random distribution,which was not ideal horizontal distribution pattern of the stands. The open degree of young forest was high,but that of half-mature and near mature forest was low,indicating that growth space of young forest was sufficient,but half-mature and near mature was lack of growth space. As Cunninghamia lanceolata grown and developed,the competition index of stands showed an increasing trend,indicating that the competition pressure among individual trees was gradually increasing with the growth of tree age. The evaluation index of stand spatial structure of Cunninghamia lanceolata ecological forest of eighteen permanent sample plots was 0. 185 9-0. 364 7,belonging to the evaluation grade 1 and 2accounting for 11% and 89% of the total sample plots respectively,without the sample plots belonging to the grade 3,4and 5,illustrating that the spatial structure of Cunninghamia lanceolata ecological forest was far from ideal spatial structure,and need to optimize the stand spatial structure. However,after thinning and replanting,the stand layer index and mingling index were increased significantly,the degree of difference among individual trees became apparent,and the growth space of juvenile and medium became more sufficient. The evaluation index of the stand spatial structure of Cunninghamia lanceolata ecological forest of nine retest sample plots was 0. 346 2-0. 613 1,belonging to level 2,3 and 4of evaluation grade accounting for 11%,78% and 11% of the total retest sample plots respectively,which illustrated that the spatial structure of Cunninghamia lanceolata ecological forest of different age groups was improved obviously.【Conclusion】There were unreasonable factors in the stand spatial structure characteristics could be found by analyzing the stand spatial structure,which provided basis for management measures to optimize the spatial structure. The evaluation index of stand spatial structure was put forward,it explored a new approach to the ideal spatial structure of Cunninghamia lanceolata ecological forest and provided the theoretical basis for the evolution of the ecological forest improving mainly Cunninghamia lanceolata plantation toward ideal structure. According to the evaluation results of spatial structure of Cunninghamia lanceolata ecological forest in the research area,it was objectively reflected the actual situation of its spatial structure before and after thinning and replanting.