2.1. Study site
The study site was located in the Yuanzegou catchment (37°14ʹ N, 110°20ʹ E) in the hilly region of the Loess Plateau, China (Figure 1). This site has a semiarid climate: the mean annual precipitation is 481 mm, approximately 70% of which falls in July, August and September (wet season); the mean annual temperature is 8.6 ℃, with the maximum of in July and the minimum of in January (Gao et al., 2014). The catchment is covered by thick loess soils (silt loam) (Gao et al., 2014). The basic soil properties of the study site are presented in Table 1.
/Figure 1/
The area of the whole catchment is approximately 0.6 km2. The uplands comprise three main land use types, i.e., jujube plantations which account for approximately 50% of the uplands, cropland, and grassland at two different growing stages (Figure 1). The jujube tree is used primarily as a shade tree that also bears fruit. The majority of the jujube trees in this catchment were planted in 2007 at a density of approximately 1650 trees per hectare, in order to improve both green cover and the farmer’s income (Gao et al., 2014). The jujube trees on hillslopes were planted in half-moon terraces (also known locally as fish-scale pits), which is one of the primary methods of planting trees on the Loess Plateau (Wei et al., 2016). The size and layout of these terraces is shown in Figure S1. In general, jujube plantations in the hilly region of the Loess Plateau are rainfed because of the high cost of irrigation, which would require runoff water collected in gully bottoms to be pumped upslope. Therefore, the jujube plantations here usually suffer seasonal droughts.