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属高寒干旱山区的甘肃省定西县华家岭,光、热、水资源严重不足.年平均气温3.4℃,年降水量仅467.4毫米,而年蒸发量则高达1212.4毫米.当地1971年在高海拔地段及梁峁、风口处栽植的杨树林带,生长不良,树冠旗状,侧枝丛生,树体未老先衰.从1987年开始,华家岭林业站对这些“小老树”居多的低产林进行改造.他们以适合当地生长的云杉为主要树种,兼营油松、落叶松、沙棘、柠条等乔、灌木.在具体改造方式上,一是按株择伐“小老树”,保留较好的中、小径木、间种云杉、沙棘、柠条,逐渐诱导成乔灌混交林;二是隔行择伐,形成针、阔、灌行间混交林.这样,多树种、多层次的混交林带相继取代了原来的“小老树”林带,为高寒干旱区改造低产林闯出了一条新路.
In the cold arid mountainous area of Gansu Province, Dingjia County, Huajialing, there is a serious shortage of light, heat and water resources, with an annual average temperature of 3.4 ℃, annual precipitation of 467.4 millimeters, and annual evaporation of up to 1212.4 millimeters. In 1971, Lots and beams, the tuyere planted poplar belt, poor growth, canopy flag, lateral branches, the tree is not old and decayed. Since 1987, Huajialing Forestry Station on these “little old tree” mostly low-yield Forest transformation.With the spruce suitable for the local growth as the main tree species, 兼营 Pinus, larch, sea buckthorn, Caragana and other trees, shrubs in the specific transformation methods, first, according to plant selection cutting “little tree” , Retaining better middle and small diameter wood, intercropping spruce, seabuckthorn, kathheit, gradually inducted into mixed forest of arbor and shrub; second interlaced selective cutting, the formation of needle, wide, filling row mixed forest.Thus, many species, Multi-level mixed forest belts have successively replaced the original “small old trees” forest belt, which has opened up a new road for the transformation of low-yield forests in the arid and arid regions.