上海市樟树单木胸径生长模型构建及其影响因素

Construction of the Single Tree Diameter Growth Model of Cinnamomum camphora in Shanghai and its Influencing Factors

为了解林分特征、气候和人为干扰等因子对上海市樟树(Cinnamomum camphora)单木胸径生长的贡献率,以上海市城市森林33个固定样地476株樟树连续3期复测数据为数据源,根据样地人为干扰、气候条件、林木大小、林分竞争指数等因子,运用多元逐步回归方法构建林木胸径生长模型,应用模型决定系数(R^(2))、均方根误差、偏差和平均绝对误差等指标筛选最佳模型并对模型预估效果进行检验。结果表明:与其他3个模型相比,胸高断面积增长量的自然对数(ln(ΔS+1))模型的决定系数(R^(2))为0.624,均方根误差、偏差和平均绝对误差分别为0.647、0.237和0.522,模型预估效果最佳;对最佳拟合模型进行方差分解,显著影响樟树胸径生长的因素依次为对数初始胸径(ln D_(1))、林分初始密度(N_(1))和年平均气温,对樟树胸径生长的贡献率为62.73%;初期胸径大小、种植密度和年均气温对樟树胸径生长有显著影响。

In order to understand the contribution of factors such as stand characteristics,climate,and anthropogenic disturbances to the diameter growth of Cinnamomum camphora in Shanghai,a sample of 476 individuals from 33 fixed forest plots was measured over three consecutive periods to serve as the data source.Utilizing factors such as anthropogenic disturbances,climatic conditions,tree size,and stand competition index,a multivariate stepwise regression method was used to construct the tree diameter growth model.The model was assessed for its predictive performance using indices including the determination coefficient(R^(2)),root mean square error,bias,and mean absolute error to select the best fitting model and test its predictive accuracy.The results showed that,compared to the other three models,the natural logarithm of the increment in cross-sectional area at breast height(ln(ΔS+1))model showed the highest determination coefficient(R^(2))at 0.624,with root mean square error,bias,and mean absolute error of 0.647,0.237,and 0.522,respectively,indicating the best predictive performance.Variance decomposition of the best-fitting model revealed that the factors significantly affecting the diameter growth of C.camphora were the natural logarithm of initial diameter(ln D_(1)),initial stand density(N_(1)),and mean annual temperature,accounting for a contribution of 62.73%.The initial diameter size,planting density,and mean annual temperature exhibiting significant influences on the tree’s diameter growth.