Throughfall and its spatial heterogeneity in a black locust (Robinia pseudoacacia) plantation in the semi-arid loess region, China

Throughfall in a forest ecosystem has potential hydrological impacts in the semi-arid loess region of China due to continuous human intervention. However, in black locust forests in this region, throughfall and its spatial heterogeneity and controlling factors remain unclear. We examined throughfall, its spatial variability and the effects of rainfall characteristics and vegetation structure on throughfall in a black locust stand experiment. Of the 489.72 mm cumulative gross rainfall during 20 sampled events, the average of throughfall for all trees, interception loss (IL) and stemflow (SF) were 380.93 mm (77.71%), 98.48 mm (20.19%) and 10.30 mm (2.10%), respectively. For a single tree, measured throughfall percentage decreased from upper to bottom in the canopy vertical layer, and the horizontal distribution increased with distance from the trunk. A correlation analysis between throughfall and rainfall characteristics, indicated that rainfall amount had a greater effect on throughfall than rainfall intensity and duration. Throughfall generally occurred following rainfall events of more than 0.76 mm for black locust. Throughfall percentage initially increased weakly, and then decreased with increasing rainfall intensity, while it initially increased, and then remained constant with increasing rainfall duration. Throughfall percentage decreased with increasing leaf area index (LAI) during differently-sized rainfall events, whereas throughfall variations were different in differently-sized rainfall events. Throughfall is affected by tree height, diameter at breast height (DBH), canopy width and canopy openness to some degree, while the effects were higher in larger storms than in smaller storms. Our study highlights the need to consider the effects of throughfall on hydrological processes, particularly for forest management in semiarid regions.