径级分布模型材积按径级分布和总材积一样,在许多森林经营决策中需要作为输入值。在生长和收获发展的一些模型中有各种方法表示按径级(一般是胸径)的材积分布,模拟直径分布是广泛用于同令林的一种方法,尤其是对南方的树种(图15——2)。这种方法各径级中每英亩树木株数是通过直径的株数相对频率的数学函数估测的,预测具有一定特点的林分(即。一定的年令,立地指数和林分密度)已知直径的树木总平均树高。将预估的平均树高和径级中值代入材积或削度公式计算各径级的材积。累计有关径级的材积而得收获估测值。虽然只需要将总的林分值(即;年令,立地指数和单位面积株数等)作为输入值,而详细的林分分布资料可以成为输出值得到。同令纯林典型的胸径分布如15——3图。这种分布通常只有一个顶点(即单峰的)而微偏。可用各种数学函数拟合这种曲线。但在过去收获研究中最常用的两种函数是β函数 Diameter Distribution Model Volumes, like the total volume, are distributed by size and need to be input in many forest management decisions. In some models of growth and harvest development there are various ways to represent the volume distribution by size (usually DBH), and the simulated diameter distribution is a widely used method for Tonglin, especially for species in the South (Figure 15 --2). In this method, the number of trees per acre in each grade is estimated by the mathematical function of the relative frequency of the number of trees in diameter. Forests with certain characteristics (ie, year, site index and stand density) are known. Diameter The total average height of the trees is high. Calculate the volume of each diameter class by substituting the estimated average tree height and diameter median value into the volume or taper formula. Accumulation of the diameter of the volume and obtain the estimated value. Although only the total stand value (ie year, site index and number of units per unit area, etc.) needs to be input, detailed stand distribution data can be obtained as output values. Pure forest with the same diameter distribution of typical DBH such as 15 - 3 map. This distribution is usually only one vertex (ie, unimodal) and slightly biased. This curve can be fitted with various mathematical functions. However, the two most commonly used functions in past harvest studies are beta functions