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河北省平原农区造林绿化工作,取得了很大成绩,现有绿化面积已达927.68万亩,林木覆盖率达8.46％。平原农区造林与山区不同,它是以营造防护林、林粮间作和四旁绿化为主,最后形成以农田林网为主体的网、带、片相结合的防护林体系。对这类林木如何计算覆盖率,还是值得研究的问题。我们在这次平原林木调查中,采用了以林木树冠投影面积计算林木覆盖率的方法,其公式:
Great achievements have been made in afforestation in the plain areas of Hebei Province. The existing afforestation area has reached 9,276,800 mu and the forest coverage rate has reached 8.46%. The planting of forests in the plain farmland is different from that of the mountainous areas. It is based on the construction of shelterbelts, intercropping of forest and grain, and greening on the four sides. Finally, a shelterbelt system combining net, belt and piece of farmland forest net is formed. How to calculate the coverage of such trees is still worth studying. In this plain survey of trees and trees, we used a method of calculating the forest coverage ratio using the projected area of tree crown, and the formula is: