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在种群发展的某一阶段,若组成种群的个体数量超过一定临界密度,就会产生密度—竞争效应。随着种群的发展,这个临界密度将会变得愈来愈小,这种密度—竞争效应是促进种群发展的主要动力之一。胸径是最容易测定的森林调查因子。在正常情况下,森林种群个体按胸径分配应趋向于正态分布。本文运用偏态分析方法,通过偏态指数和偏态比来表示偏离正态分布的程度,可随时检验密度—竞争效应,以便采取调节措施。对森林种群来说,当偏态指数为“0”时是典型的正态分布,而偏态比在-3—+3范围内,基本上属正态分布:当偏态比>+3为“L”型群体,必须采取下层抚育间伐措施;当偏态比<-3为“J”型群体,应采取下层和上层相结合的综合抚育间伐。这样调节密度—竞争效应和林木种群结构,就可提高森林生产率,文中举了不同密度的刺槐人工纯林和接近天然状态的飞播马尾松林作为实例进行论证,说明偏态分析对检验种群密度—竞争效应是一个较简易的方法。
At a certain stage of population development, if the number of individuals that constitute a population exceeds a certain critical density, a density-competitive effect will result. As the population grows, the critical density will get smaller and smaller. This density-competition effect is one of the major motivations for population development. DBH is the easiest forest surveyed. Under normal circumstances, individual distribution of forest population should tend to be normal distribution according to DBH. In this paper, we use the skewness analysis method to express the deviation from the normal distribution by the skewness index and skewness ratio. The density-competition effect can be tested at any time in order to take adjustment measures. For forest populations, the skewness index is a typical normal distribution when the skewness index is “0” and the skewness ratio is essentially normal distribution over the range of -3 - +3: when the skewness ratio> +3 is For “L” type of population, it is necessary to take the measures of lower tending and tending; when the skewness ratio <-3 is “J” type, comprehensive tending thinning should be adopted. In this way, the density-competition effect and the structure of forest population can improve the productivity of forests. The paper presents different density artificial forests of Robinia pseudoacacia and Pinus massoniana forests close to the natural state as an example to demonstrate that skewness analysis is of great significance for the test of population density-competition The effect is a simpler method.