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Response of Soil Moisture to Long-Duration Rainstorms in Three Forest Stands in Mountainous Areas of North China

Rainfall is one of the core components of the water cycle in terrestrial ecosystems and is closely related to hydrothermal balance, plant and animal growth, and stability of the whole ecosystem. Long-duration rainstorms can alter the soil structure of forest ecosystems and affect the spatial distribution of soil moisture, thus affecting the water supply from the soil to trees and being one of the factors that increase the vulnerability of forest ecosystems. In recent years, changes in rainfall patterns have normalized prolonged heavy rainfall in the mountainous areas of North China. However, there are few reports on the response of soil water at different depths to historically long rainstorms in forested areas. By quantifying the relationship between precipitation characteristics and soil water, the soil water transport patterns of Platycladus orientalis (PO), Quercus variabilis (QV) and Pinus tabuliformis (PT) during the long-duration rainstorms of 21–22 July 2012 were evaluated separately, and the roles of different plants in response to the historically long rainstorm were determined. The results showed that (1) the response of different forest stands to rainfall had a lag. Among them, the soil water of PO and PT were less affected by rainfall and could maintain a relatively stable state. (2) The soil moisture transport trend of PO was significantly greater than that of other vegetation zones and covered the whole process of rainfall. Under the three typical vegetation covers, there was a continuous zero-flux plane in the soil at each observed depth (the direction of soil moisture flow is more stable over the rainfall period), but there was no regular transport trend. (3) The root system was an important factor, influencing the differences in soil moisture response of the three vegetation types. QV had a higher average effective water recharge rate than lateral cypress and oleander and could better utilize the water recharge from storm water.