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林分在其生长发育的各个阶段，都有一个最佳密度，使得最终主间伐合计的总收获量最大。为了找到这一密度系列，根据１９９４年在内蒙古大兴安岭林管局收集的２００块标准地及３９１株解析木的资料，以立木密度（Ｎ）作为控制变量，以林分蓄积为状态变量，以各阶段间伐的总收获量最大作为目标函数，利用动态规划的方法进行推导，得出了天然白桦林的最优密度模型。利用该模型，可以得到不同立地条件，不同年龄阶段的理论最优密度。对天然白桦林的营养面积进行了研究，提出了用树高承担值确定保留木株数的方法，只要根据年龄和立地条件确定树高承担值，就可通过优势木平均高获得营养面积，进而求得保留木株数。这种方法简便而实用，便于在生产实践中应用。
Stands have an optimal density at all stages of their growth and development, maximizing the total final harvest achieved by the final master thinning. In order to find out the density series, according to the data of 200 standard plots and 391 analytical trees collected in 1994 by the Daxinganling Forest Management Bureau in Inner Mongolia, the stand density (N) was used as the control variable and the stand volume was used as the state variable The maximum total harvest of the stage was taken as the objective function, and the optimal density model of natural birch forest was obtained by using the method of dynamic programming. Using this model, we can get the theoretical optimal density of different site conditions and different age stages. The natural area of birch was studied, and the method of determining the number of preserved wood with tree height was put forward. As long as the height of tree height was determined according to age and site conditions, the average area of nutritive wood could be obtained by superior wood, To retain the number of wood. This method is simple and practical, easy to use in production practice.