黄土半干旱区不同密度刺槐林地的土壤水分动态

Soil Moisture Dynamic of the Robinia pseudoacacia with Different Density in Semiarid Region on the Loess Plateaus

通过对1998—1999年5—10月2个生长季不同密度刺槐林的连续观测,研究林地土壤水分运动规律及年际变化特征。结果表明:春季不同密度刺槐林地的土壤水分差异较小,并有随林分密度增大而减小的趋势,林分密度越小土壤深层储水量越高。不同密度的刺槐植树带随着林分密度的增大,渐渐隐现出干旱、半干旱地区成林的土壤干化现象,而且随着降水的减少和林木个体水分消耗的递增,林分内水分供需矛盾越来越显著。对于自然集水斜坡面积在8m^2以上的刺槐植树带内,深层土壤水分能得到较好的补偿。随着林分密度的增大,林下植被种类和数量越来越少,逐步由中生植物向旱生植物过渡,其生物总量、盖度、长势和植物体含水量也随之降低,反映出林地土壤的水分环境容量随林分密度变化的特征。

The motive rule and annual dynamic of soil moisture were studied based on continuous observing the woodland of Robinia pseudoacacia with different density in two growing seasons from May to October, in 1998 and 1999. The observation was carried out once every 10 days and the depth observed is 2 m. The results showed that difference of soil moisture is just about 2% in the woodland of Robinia pseudoacacia with different densities in spring and it has a decreasing trend with the increasing density. When the stand density is sparse, soil water in deeper layer will rise. It showed the phenomenon of soil desiccation with the density increasing in the woodland of Robinia pseudoacacia like the matured stand of the arid and semiarid regions. With the decreasing of water and the gradual increase of water consumption by individual tree, the conflict of water supply and demand was more pronounced. Soil water in deeper layer may be compensated in the area of 8 m in the woodland of Robinia pseudoacacia from water harvesting. The species and quantity of undergrowth are gradually reduced with the increase of stand densities. And it will change from the mesophyte to xerophil. The biomass, coverage, growth and the moisture capacity of plant in the community could be reduced with the increase of stand densities, too. The results showed that the soil water environment will transform with different stand densities in forest.