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在美国东部与东北部的国有林里,经常发展同龄树种的混交林结构(由年龄没有差别或差别不大的林木所组成,其最大允许年龄差一般为10—20年),选用同类属性的树种,使其形成上层树冠及下层树冠。根据各类同属性树种的生物学特性以及直径级幅度,使林分垂直分层(分类)。森林经营者和生态学家们就把这些林分当做全龄的(林分具有全部或几乎全部龄级的树木)进行经营。并根据此对林分进行择伐,以防止林分退化。控制这种混交林在同一龄级范围之内,在管理方面比纯林经济,同时能形成更有利于树木生长的生态环境。事实说明,发展同类属性树种的混交林,除容易管理外,还可大大减少造林费用,提高木材产量及质量。
In national forests in the eastern and northeastern United States, mixed tree structures of the same age are often developed (composed of trees with no difference or little difference in ages and the maximum allowable age difference is generally 10-20 years) Tree species, to form the upper canopy and the lower canopy. According to the biological characteristics of all species with the same properties and diameter-class amplitude, the stands are stratified (classified) vertically. Forest managers and ecologists operate these stands as full-age (trees with all or almost all age classes). And based on this selective cutting of the forest in order to prevent degradation of forest stand. Control of this mixed forest in the same age range within the management of pure forest economy, but also can form more conducive to the growth of trees in the ecological environment. Facts show that the development of mixed species of trees with the same properties, in addition to easy management, but also greatly reduce afforestation costs and improve timber production and quality.