Comparison of Changes in Soil Moisture Content Following Rainfall in Different Subtropical Plantations of the Yangtze River Delta Region

Rainfall is an indispensable link in the atmospheric water cycle, which plays a critical role in forest hydrology. Quercus acutissima and Cunninghamia lanceolata are two fast-growing and economically important tree species in the middle and lower reaches of the Yangtze River. They are extensively applied in the restoration of vegetation, hydraulic engineering, and the development of artificial forests. The primary aims of this study were to describe and compare the changes in soil water content following rainfall events, while elucidating their relationships to environmental factors. From September 2012 to August 2013, we monitored the soil moisture at different depths every 30 min using commercially available soil moisture measuring devices. Hourly meteorological data were monitored over an open area at 200 m from the sample site, including photosynthetically active radiation (Par), air temperature (Ta), relative air humidity (RH), vapor pressure deficits (Vpd), rainfall, and wind speed. The results revealed that variations in the soil moisture content during summer (Cv = 0.231) and autumn (Cv = 0.0.170) were greater than during spring (Cv = 0.0.092) and winter (Cv = 0.0.055), with those in the deep soil moisture (Cv = 0.117) being smaller. The soil moisture content was significantly altered following the cessation of rainfall, where the initial and average moisture content, and the ACR of the soil increased with higher rainfall intensities. The ACR was positively correlated with Ta (γ = 0.16), RH (γ = 0.46) and rainfall (γ = 0.22), but negatively correlated with Par (γ = −0.29), Vpd (γ = −0.23), and wind speed (γ = −0.01). This study provides valuable information regarding the hydrological processes of artificial forests in the middle and lower reaches of the Yangtze River.