I-72杨林的竞争密度效应

用竞争密度(C—D)效应的倒数式(即t/w=Api B，式中w和pi分别为平均单株材积和密度，A和B为系数)分析了I-72杨林的生长过程。在双对数图上，I-72杨林各生长阶段的平均单株材积和密度的观察值很好地吻合了竞争密度效应曲线，竞争密度效应曲线随时间的推移向上移动。通过分析得出了生物时间τ(逻辑斯蒂生长曲线中生长系数λ(t)的积分)，系数A和B，生长系数λ(t)和最终收获量Y(t)的变化趋势及系数A和B的生物学意义。生物时间τ随着物理时间t的增加而增加。随着τ的增加，系数A急剧增加到最大值后逐渐下降，而系数B呈指数下降，倾向于接近零。随着林分的生长，生长系数λ(t)倾向于下降，而最终收获量Y(t)逐渐增加。以C-D效应为基础，提出了对高密度的7a生I-72杨林进行间伐的建议。

THE COMPETITION-DENSITY EFFECT IN POPULUS × EURAMERICANA CV.'SAN MARTION' PLANTATIONS

The reciprocal equation of the C-D effect, i.e. 1/w = Aρi+B (w and ρi respectively represent mean stem volume and density, A and B are coefficients) was used to describe the C-D effect in Populus × euramericana (Dode) Guinier cv. `San Martion' plantations. The data observed from different growth stages were well fitted with the C-D curve given by the reciprocal equation of the C-D effect on logarithmic coordinates, and the C-D curve shifted upward with the progress of time. The change trends of biological time τ, the coefficient A and B, the coefficient of growth λ(t) and the final yield Y(t) were given. The biological meanings of coefficient A and B were obtained. Biological time τ increased gradually with physical time t. With increasing τ, the coefficient A increased abruptly up to its maximum value, and then decreased gradually, whereas the coefficient B decreased exponentially and tended to close to zero. With stand growth the coefficient of growth λ(t) decreased gradually and final yield Y(t) increased gradually. Based on the C-D effect, intermediate cutting for 7-year-old P. euramericana plantation with high-density was proposed.