Influence of Canopy Interception and Rainfall Kinetic Energy on Soil Erosion under Forests

Abstract

Afforestation is a widely accepted measure to control soil erosion around the world. A large area of forest has been built to prevent slope soil erosion in the red soil region of southern China since the 1980s. The vegetation coverage has significantly increased; however, there is still moderate or severe soil erosion under the forest. In order to improve the situation, it is necessary to study the effects of canopy on soil erosion under the forest. Standard runoff plots were established on two typical sites, which represented pure Pinus massoniana Lamb. forest and bare land, respectively. Precipitation redistribution and throughfall indices including raindrop size, raindrop velocity, and the kinetic energy (KE) of raindrops were quantified. The results showed that 29.3% of the precipitation was directly prevented from reaching the forest land surface. The canopy interception effect was better under low rainfall intensity than high rainfall intensity. Compared with open rainfall, throughfall raindrops were 16.3% fewer in number, larger in size, and the range of throughfall drop size distribution (DSD) was enlarged. The volume ratio of large drops was larger with higher rainfall intensity. When the rainfall intensity was less than 14 mm h−1, throughfall kinetic energy (TKE) was higher than open rainfall kinetic energy (OKE) owing to the higher volume ratio of large raindrops. When the rainfall intensity was more than 14 mm h−1, TKE was smaller owing to the large raindrops failing to reach their final velocities: their mean velocity was 80% of their final velocity. The sediment yield was the largest under high rainfall intensity and the effect of sediment reduction was the largest under moderate rainfall intensity. Therefore, the largest KE did not lead to the maximum sediment yield; canopy interception was also an important factor affecting sediment yield.