Researchers studied soil water characteristics under different tree species in Beijing's Xishan area. They found that soil in Platycladus forests retains more water than in R. pseudoacacia forests. The upper soil layer holds more water than the lower layer in both forests. R. pseudoacacia has a higher water supply capacity than Platycladus. The boundary point between easily and less easily available water in the soil is 0.3 MPa for both tree species.