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南方集体林区的森林,随着经营年限的增长,林分结构发生了根本变化。原始林的比重逐年下降,而人工林的比重逐年加大。木材生产已由过去的大面积皆伐(原始林)逐步过渡到人工林的抚育间伐(以下简称间伐)和小面积皆伐、择伐。全国有用材林面积14.7亿亩,其中中幼林面积为9.7亿亩(大部分为人工林),占用材林面积的66％。由于间伐集运材方式没有得到很好解决,致使大量的中幼林不能及时进行间伐。目前急待进行间伐的中幼林面积达4.5亿亩,这样
The forests in the southern collective forest areas have undergone fundamental changes in their stand structure with the increase of their operating years. The proportion of primary forest decreased year by year, while the proportion of plantation increased year by year. Timber production has been gradually evacuated from large-scale clear cutting (virgin forest) to tending thinning of planted forests (hereinafter referred to as thinning) and to small-area clear cutting and selective cutting. The national useful timber forest area is 1.47 billion mu, of which young and middle-aged forests cover an area of 970 million mu (mostly artificial forests), accounting for 66% of the total area of timber forests. Since the method of thinning the collection material has not been well solved, a large number of young and middle-aged forests can not be thinned in time. Currently in urgent need of thinning in the area of 450 million mu of young and middle-aged, so