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黑龙江省西部地区早期营造的农田防护林,已经发挥了护田增产作用,在有效防护区内平均增产率达18%。但是随着林带的逐年成长,与受益的同时,相对的也产生了一定的副作用,即在林带两侧附近的一段距离内,形成了胁地现象,影响了农作物的生长,并造成不同程度的减产,而胁地的范围将随树高不断增加而扩大。根据在龙江、太来、林甸、肇州等四个县的典型调查,林带两侧胁地距离为树高的1至1.5倍,一般减产率为40—60%。为此,通过摸清规律,才能采取措施,减少胁地和防止发展,以利于农业生产。一、形成胁地的主要原因现有林带宽度多为10米,栽植7行,走向多为南北和东西,其中以北、东侧胁地尤为明显。林带的林缘附近形成胁地的因素是综合性的,而其主要原因:第一、由于树木树冠投影,在一定距离内,形成了周
The farmland shelterbelts initially constructed in the western Heilongjiang Province have already played a role in boosting the output of paddy fields and the average yield increase rate in the effective shelter zone has reached 18%. However, as the belt grows year by year, it also has the relative side benefit as well as the relative benefit. At the same time, there is a threat of land formation within a certain distance near both sides of the belt, affecting the growth of crops and causing different degrees of Cut, while the scope of the land will be increased with the increasing tree height. According to the typical survey in four counties of Longjiang, Tailai, Lindian and Zhaozhou, the shelter distance on both sides of the forest belt is 1 to 1.5 times of the tree height, and the general yield reduction rate is 40-60%. Therefore, by studying the law, we can take measures to reduce the threats and prevent development so as to facilitate agricultural production. First, the main reason for the formation of threatening The existing forest width of 10 meters mostly, planted seven lines, to the north and south and east and west, of which north and east of the threat is particularly evident. The factors that form the threat of land near the forest edge of the forest belt are comprehensive, and the main reasons are as follows: First, due to the canopy projection of the trees, within a certain distance, a week