小流域防护林适宜覆盖率与植被盖度的理论分析

Forest coverage of small watershed and stand density in the gullied-hilly region on Loess Plateau

从防止水土流失和土壤水分容量两个方面出发,分析了以森林植被为主体的植物系统的覆盖率、植被盖度与形成良好的健康的森林水分生态环境和水土保持功能的关系。分析了小流域森林覆盖率与水蚀的关系,地块尺度上植被盖度与水蚀的关系。提出根据最大土壤侵蚀量、年允许土壤流失量和小流域的水分供应关系来确定区域宜林地林分面积与适宜森林覆盖率。根据水分、树种、林龄和立地条件对森林密度做具体分析。研究表明:在黄土区小流域尺度,合理的森林分布是防治水蚀的关键;适宜植被盖度是保证水土保持功能持续的关键,乔木成林林分郁闭度达到40%,草本植物的盖度达到90%就具有较好的防蚀功能,植被盖度与生物量同时处于适宜状态时,林分的水土保持功能最佳。研究认为水土保持有效植被盖度不应低于有效盖度(群落下土壤流失量等于允许流失量),最大为临界盖度(群落下土壤流失量为自然侵蚀量),群落灌层下死被物应具有一定厚度为1.0～2.0cm。研究表明在山西省吉县,阳坡刺槐造林密度小于2250株/hm2,以1111株/hm2为最佳;成林密度为300～1800株/hm2,以小于1500株/hm2为佳。

The research start from two aspects： prevent soil erosion and soil moisture capability to analyse the function relationship between two aspects ： one is the protective function of vegetation ecosystem, forest coverage and vegetation coverage, the other is the well function of soil and water conservation. The relationship between vegetation coverage and water balance, and the relationship between vegetation coverage and erosion were ana- lyzed. According to the analysis, the methods to decide the suitable forest coverage and vegetation in the small watershed scale and plot scale were given. The research indicated the suitable density of forest is the key to prevention and cure water erosion in the semihumid area on the Loess Plateau. Suitable vegetation coverage is the key to ensure soil and water conservation function. If the canopy density of standing forest of arbor can reach to 40% and cover degree of herbage can reach to 90% , then the function of anticorrosion is good. When vegetation coverage and biomass are suitable simultaneously, function of soil and water conservation of standing forest is optimum. The research indicated the effective vegetation cover age in soil and water conservation is higher than effective cover degree, the maximum is the critical cover degree. The dead vegetation under bush level of community should have constant thickness, which is 1.0 - 2.0cm. The research in Ji County of Shanxi Province showed forestation density of locust tree on sunny slope is less than 2250 trunks per hm^2 , 1111 trunks is optimum ; adult growth is 300 - 1800 trunks per hm^2, less than 1500 trunks per hm^2 is optimum.