Abstract: Soil moisture content is the basic indicator for studying soil moisture conditions and dynamics, and it is one of the important indicators for long-term observation of terrestrial ecosystem water environment. Evergreen deciduous broad-leaved mixed forest is a zonal vegetation type in the northern subtropical zone of China. The observation area is located in the Mount. Shennongjia Area in western Hubei Province, which is the important catchment area of the Three Gorges Reservoir and the middle route of the south-to-north water diversion project. This dataset collected soil moisture content data from May 2009 to December 2016 at the National Observation and Research Station for Forest Ecosystem in Shennongjia, Hubei, China (also known as Shennongjia Biodiversity Research Station of the Chinese Academy Sciences, SNF for short), with a total of 7,425 entries. The determination method is fixed-point continuous observation by instrument of Time Domain Reflectometry (TDR). The observation depths are 0–10 cm, 10–20 cm, 20–30 cm, 30–40 cm and 40–50 cm with observation frequency of 2 times per month. There are 9 measuring tubes in total. Each three measuring tubes are buried in the upper part, middle part and lower part respectively of the artificial runoff field of 20 m×5 m (horizontal projection). Users can conduct data retrieval based on observation time, observation depth and slope position. Preliminary statistics show that: 1) The average soil moisture content (volume ratio) of evergreen deciduous broad-leaved mixed forest from 2009 to 2016 is 0.313 (±0.165), the maximum value is 0.647, and the minimum value is 0.000; 2) In terms of soil moisture content, the highest value is 0.342 in 2009 (from May to December), followed by 0.340 in 2012, and the lowest value is 0.293 in 2010; 3) The soil moisture content is the highest in January, 0.343, and the second highest in November, 0.342; the lowest in August, 0.271, followed by July, 0.291; 4) Soil moisture content from the upper to the lower layer gradually increases, with its values being 0.084 (±0.070), 0.222 (±0.092), 0.359 (±0.108), 0.431 (±0.078) and 0.468 (±0.065) respectively for 10 to 50 cm soil layers ; 5) The average soil water storage capacity of 0 to 50 cm soil layers from year 2009 to 2016 is 156.99 (±18.66) mm, equivalent to 1569.9 (±186.6) t/hm2. Creating and sharing a soil moisture content database in a northern subtropical evergreen deciduous broadleaf mixed forest can provide data for understanding water conservation and water regulation functions in the water catchment areas of water conservancy projects. It also can provide data for understanding the soil moisture dynamic characteristics of this type of forest and its response to climate changes amid global changes in future. It is of great significance to the water balance and hydrological cycle of regional forest ecosystem. It can help promote scientific studies on the forest hydrology of mixed evergreen deciduous broad-leaved forest and has great significance for the study of forest hydrology in China.
Keywords: soil moisture content; Time Domain Reflectometry; mixed evergreen and deciduous broad-leaved forest; north subtropical; SNF