在皇甫川流域,随着林草覆盖度的增加,植被与水的矛盾日益突出,其中一个重要的问题就是植被密度与土壤水分之间的矛盾。土壤水分的降低影响了植被的生长,甚至导致了部分植被的死亡,因此对土壤水分与植被密度之间的关系进行研究非常重要,有助于合理造林密度的确定。在已有研究及实验观测的基础上,建立了柠条(Caragana intermedia)林地土壤水分动态模拟模型,模型考虑了主要的土壤、植物过程,包括土壤性状、降雨入渗、植物蒸腾、地表蒸发等;模拟了从1971至2000年,30年里各种立地条件(不同盖度、坡向和坡度)下的柠条林地土壤水分、蒸腾和蒸发等的日动态过程。通过比较不同立地条件下的土壤水分动态,研究了皇甫川流域典型柠条林地土壤水分与植被盖度、坡向和坡度之间的关系,并得出了它们之间的关系式。由得到的平地上柠条的适宜密度,同时结合上述关系式,得出了不同坡度、坡向的适宜密度。坡度小于10°时,适宜造林密度对坡度反应敏感,在10°~30°时,适宜盖度对坡度反应不敏感。对于小于10°的坡地,植被建设时要特别注意设计合理的植被密度。

With an increase in vegetation coverage, there can be a decrease in soil water content due to uptake and evapotranspiration by the vegetation. At high planting densities, poor growth and even mortality has occurred due to the decrease in soil water content. Hence, a better understanding of the relationship between soil water content and the density of plants is important for designing effective restoration projects. To study these relationships, we developed a soil water dynamic simulation model of a Caragana intermedia woodland under different slope gradients and slope aspect in the Huangfuchuan watershed conditions based on previous studies and field experiments. The model took into account soil characteristics, precipitation infiltration, vegetation transpiration, and soil evaporation. Daily changes in soil water content, transpiration, and evaporation of Caragana intermedia woodlands with different vegetation coverage, slope gradient, and slope aspect was simulated from 1971 to 2000. Through model simulations, we determined the functional relationships among soil water content, plant coverage and slope as well as the optimal plant density on flat slopes. With further simulations, we determined the effects of slope gradient and slope aspect on soil water content. When slope gradient was less than 10 degrees, the optimal planting density was sensitive to slope gradient. In the range of 10 and 30 degrees, planting density was not sensitive to slope gradient. Therefore, when reconstructing vegetation, it is important to consider planting densities on the hillsides with slope gradients less than 10 degrees.