Application of stand density indices for Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) plantation management

The most important issues in Chinese fir (Cunninghamia lanceolata (Lamb.) Hook) management are the quantitative determination of stand density and the selection of appropriate density. Different stand density index models have advantages for special tree species, and this study aimed to estimate the carrying capacity of planted stands of Chinese fi r and to select simple and reliable stand density indexes. Based on special experiment of different initial density, the maximum carrying capacity was estimated using Reineke’s self-thinning rule, Nilson’s sparsity theory, Beekhuis’s relative-spacing hypothesis, Zhang’s nutrientcompetition rule, Curtis’s maximum stand basal area and Hui’s crowding degree based on mean tree distance. The restricted maximum likelihood method (REML) implemented with ‘nlme’ package in R software was used to refi ne the parameters of thinning age in Richard’s growth model. The results showed that stand density index models can describe the trends of stand density in response to tree growth the higher the plantation initial density, the earlier age and stronger self-thinning capacity of stands. Reineke’s SDI and Zhang’s Z model are the most stable and suitable to estimate changes in the density of Chinese fi r plantations, competition intensifi cation, and the thinning age. The RD model can also be used, except at low Chinese fi r densities. K, which can be affected by the mean crown width of trees, directly refl ects the forest area of photosynthesis; this index is easy and simple to apply, but more research is needed to optimize the equation to evaluate whether a forest requires management and to determine the appropriate time for the fi rst thinning and its intensity.

杉木（Chinese fir，学名Cunninghamia lanceolata (Lamb.) Hook）经营中最核心的问题，在于林分密度（stand density）的定量测定与适宜密度的遴选。不同林分密度指数模型对特定树种均有其适配优势，本研究旨在估算杉木人工林的承载容量，并筛选出简便可靠的林分密度指标。基于不同初始密度的专项试验，本研究分别采用赖内克自然稀疏法则（Reineke’s self-thinning rule）、尼尔森稀疏理论（Nilson’s sparsity theory）、比克休斯相对株距假说（Beekhuis’s relative-spacing hypothesis）、张式养分竞争法则（Zhang’s nutrient-competition rule）、柯蒂斯最大林分断面积模型（Curtis’s maximum stand basal area）以及基于平均树距的惠氏拥挤度模型（Hui’s crowding degree based on mean tree distance），对杉木人工林的最大承载容量进行估算。利用R软件中nlme包实现的限制性最大似然法（restricted maximum likelihood method, REML），对理查德生长模型（Richard’s growth model）中的抚育年龄参数进行优化拟合。研究结果表明，林分密度指数模型可有效刻画林分密度随林木生长的变化规律：人工林初始密度越高，林分启动自然稀疏的年龄越早，自然稀疏能力越强。赖内克林分密度指数（SDI）与张式Z模型稳定性与适配性最佳，可精准估算杉木人工林的密度变化、竞争加剧程度及抚育年龄。除低林分密度场景外，相对距离（RD）模型同样适用。K值可直接反映森林光合面积，其大小受林木平均冠幅影响；该指标操作简便，但仍需开展更多研究以优化其评估方程，用于判断森林是否需要经营、确定首次抚育的适宜时机及抚育强度。

搜集汇总

背景与挑战

背景概述

该数据集聚焦于杉木人工林管理，旨在评估多种林分密度指数模型（如Reineke's SDI和Zhang's Z模型）的适用性。研究通过分析不同初始密度实验数据，确定这些模型在预测林分密度变化、竞争强度和间伐时机方面的稳定性与效果。