Relationship Between Soil Moisture of Robinia pseudoacacia Forests and Aboveground Biomass of Understory Vegetation

In order to understand the relationship between soil moisture and aboveground biomass of under- story vegetation in Robinia pseudoacacia forests in Loess hilly region,20 plots were sampled,including 16 Robinia pseudoacacia Forest plots at different age and 4 abandoned field plots over 25 years.The results showed that soil moisture of all Robinia pseudoacacia forest plots was significantly lower than that of aban- doned fields and soil moisture reduced with age of trees increasing.The variation of soil moisture in 0-40 cm profile in growth season followed a law:overmature forestmature forestyoung forestabandoned field,but reversed in 140—500 cm soil layer.Aboveground biomass of understory vegetation in overmature and mature forests was slightly higher than that in abandoned fields.Soil moisture content was almost not correlated with aboveground biomass.We concluded that Robinia pseudoacacia did not effect the productivity of land,although it consumed much water in soil and make it dryer and dryer.So,Robinia pseudoacacia should be used as a pincer tree spieces to restore degraded ecosystem in Loess hilly region.