Abstract: Understanding the relationships between spatial structure of forest stand and the hydrological effects of canopy, litter and soil layers is important for the sustainable management and water conservation functioning of plantations. In this study, we analyzed the relationships between spatial structure parameters (angle scale, size ratio, openness, competition index, and canopy layer index) and the hydrological effects of canopy, litter and soil layers in Pinus tabuliformis plantations with six stand densities (1000, 1800, 2700, 3600, 4400, and 5200 trees·hm^-2) in Caijiachuan watershed in Jixian County, Shanxi Province. The results showed that Pinus tabuliformis plantation with a density of 1000 trees·hm^-2 exhibited the most optimal spatial structure, characterized by weaker competition among trees, higher openness, and a more complex canopy structure with a higher proportion of dominant trees. With increasing stand density, spatial structure deteriorated. At the density of 1000 trees·hm^-2, the maximum canopy interception was 7.30 t·hm^-2. At the density of 2700 trees·hm^-2, litter accumulation, the maximum litter water-holding capacity, and the maximum soil water-holding capacity (0-100 cm) were the highest, at 26.69 t·hm^-2, 4.11 mm, and 52.33 mm, respectively. Therefore, regulating stand density to 2700 trees·hm^-2 maximized the overall hydrological effect evaluation index for the canopy, litter, and soil layers. The size ratio was significantly negatively correlated with litter accumulation, maximum litter water-holding capacity, maximum soil water-holding capacity, and capillary water-holding capacity (P<0.05). Soil non-capillary water-holding capacity was significantly positively correlated with openness (P<0.05) and negatively correlated with competition index (P<0.05). The size ratio, canopy layer index, and openness were key spatial structure parameters affecting the hydrological effects of Pinus tabuliformis plantation.

Key words: Pinus tabuliformis, forest plantation, stand spatial structure, litter layer, soil layer, hydrological effect