巨尾桉人工林林分因子与林龄的关系模型及样地尺度效应

Correlation and Sampling Scale Effect between Stand Factors and Age of Eucalyptus grandis×E.urophylla

揭示广西壮族自治区南宁巨尾桉人工林(2~9 a)的林分特征,研究主要林分因子与林龄的相互关系及在不同面积尺度上的适应性。巨尾桉人工林设置20个(30 m×30 m)方形大样地,每个方形样地中分成9个小样地(10 m×10 m),由4个小样地组成中样地(20 m×20 m)。采用Logistic、Gompertz、Richards和Korf等4种经验模型模拟林分密度、平均直径、平均高、优势木高、胸高断面积、蓄积量等主要林分因子与林龄的相互关系。巨尾桉人工林林分平均直径、平均高、优势木高等林分与林龄呈极显著正相关,回归关系用Logistic经验模型拟合最好,相应3组检验决定系数(R^2)均>0.5,3组测试样地的标准化残差落在[-2,2]带状区域中,表明3个模型在不同面积尺度样地上有较好的适应性;胸高断面积和每公顷蓄积量与林龄呈显著正相关,回归关系分别用Gompertz经验模型和Korf经验模型拟合最好,胸高断面积-林龄模型很好地适应中小样地(100、400 m^2),在大样地(900 m^2)中稍差;蓄积量-林龄模型很好地适应大、小样地(100、900 m^2),在中样地(400 m^2)中稍差。巨尾桉人工林林分胸径分布呈现近似正态分布,呈现增长型趋势;林分平均直径、平均高、优势木高与林龄回归关系用Logistic经验模型拟合最好,100 m^2样地大小已具备反映这3个林分因子与年龄的生长规律;胸高断面积和每公顷蓄积量与林龄回归关系分别用Gompertz经验模型和Korf经验模型拟合最好,胸高断面积、蓄积量与林龄的相关性具有较大的空间异质性;林分密度与林龄无显著相关性。

To understand the stand characteristics of Eucalyptus grandis×E.urophylla plantations(2-to 9-year-old)occurring in Nanning of Guangxi;to study the relationships between the main stand factors and stand age;to examine the adaptability of the models in different area scales.Twenty big sample plots(30 m×30 m)were set up within the E.grandis×E.urophylla plantation.Each plot was further divided into 9 small sample plots(10 m×10 m).A medium size plot was constructed by 4 small sample plots(20 m×20 m).Four empirical models,including Logistic,Gompertz,Richards and Korf models,were used to analyze the relationships between main stand factors(such as stand density,average DBH,mean height,dominant tree height,section area of breast height,and stand volume,etc)and stand age.Stand factors,such as average DBH,mean height and dominant tree height,were positively correlated with stand age,which were best fitted by Logistic empirical model.The R2 of three test samples were all greater than 0.5,and the standard residuals of three test samples fell in the[-2,2]strip region,indicating that the three models had good adaptability in different area scales(100,400,and 900 m2).In a similar way,section area of breast height and stand volume presented significantly positive correlation with stand age,which were best fitted by Gompertz empirical model and Korf empirical model,respectively.The relationship model of section area of breast height and stand age was well adapted to the medium and small sample plots(100 and 400 m2),but not to the large sample plots(900 m2).The relationship model of stand volume-stand age well adapted to the big and small sample plots(100 and 400 m2),but not to the medium sample plots(400 m2).The DBH distribution of E.grandis×E.urophylla plantation showed an approximate normal distribution and an increasing trend.Stand factors,including average DBH,mean height and dominant tree height,were positively correlated with stand age,which were best fitted by Logistic empirical model.The sample plot with an area of 100 m2 was sufficient to establish the growth law reflecting the three stand factors and stand age.The regression relationship between section area of breast height,stand volume and stand age was best fitted by Gompertz empirical model and Korf empirical model,respectively.The correlation between section area of breast height,stand volume and stand age had great spatial heterogeneity.There was no significant correlation between stand density and stand age.