栎类次生林自稀疏条件下的林分空间结构单元划分方法

Methods for dividing the spatial structural units of oak secondary forest under self-thinning condition

【目的】划分栎类次生林自稀疏结构单元,是应用林分自稀疏发生规律开展栎类次生林经营的基础性工作。【方法】以湖南省2009年和2014年两期森林资源连续清查数据中6块栎类次生林样地为数据源,使用3种林分空间结构单元划分方法,分别得到若干个结构单元,计算各结构单元内林木的株数密度和平均胸径,建立Reineke密度指数模型,比较模型的拟合效果和检验效果。【结果】方法1、方法2和方法3所得样本拟合的自稀疏边界线R^(2)分别为0.882、0.780、0.893;RMSE分别为0.180、0.229、0.169;方法3的拟合效果最好。3种方法的检验结果中,方法3对自稀疏判断的正确率为72%,检验效果较好;其余2种方法均低于50%。【结论】3种结构单元划分方法中,方法1忽略了距离死亡木较远的样木;方法2没有考虑位置不同的样木对死亡木影响的差异;方法3(Voronoi图+样圆权重法)更为完整地统计了对自稀疏有影响的样木,并区分为Ⅰ类样木和Ⅱ类样木,分别计算权重,分析其对死亡木影响的差异。方法3是一种考虑了林木空间分布差异,同时还依据对死亡木影响大小区分样木类别的林分空间结构单元划分方法。

【Objective】The division of self-thinning structural units of oak secondary forest is the basis of applying the law of self-thinning of forest to carry out the management of oak secondary forest.【Method】Based on the data of forest resources continuous inventory in 2009 and 2014 in Hunan province,6 oak secondary forest plots were used as data sources,three methods of spatial structure unit division were used to obtain several structural units,and the plant number density and average DBH of trees in each structural unit were calculated to establish the Reineke density index model.The fitting effect and testing effect of the model were compared.【Result】The self-thinning boundary lines R2 fitted by the samples obtained by methods 1,2 and 3 were 0.882,0.780 and 0.893,respectively.RMSE were 0.180,0.229 and 0.169,respectively.Method 3 had the best fitting effect.Among the verification results of the three methods,the correct rate of method 3 was 72%,and the verification effect was the best.The other two methods were below 50%.【Conclusion】Among the three structural unit division methods,method 1 ignored the sample wood far away from the dead wood;Method 2 did not consider the difference of the effects of different locations of sample trees on dead trees;Method 3 (Voronoi diagram + sample circle weight method) more completely counted the sample trees that had influence on self-thinning,and divided them into Class I and Class II samples,calculated the weights respectively,and analyzed the difference of their influence on dead trees.It is a division method of stand spatial structure unit,which considers the difference of spatial distribution of trees and distinguishes the types of sample trees according to the influence of dead trees.