不同自然降雨等级下不同郁闭度马尾松林的水土流失特征

为揭示南方红壤侵蚀区不同郁闭度马尾松林水土流失的规律,以长汀红壤侵蚀区不同郁闭度(0.2,0.4,0.6,0.8)马尾松林为研究对象,采用标准径流小区观测的方法,利用在2015年观测的37场自然降雨事件构成一个降雨梯度,分析不同郁闭度马尾松林水土流失随降雨等级的变化规律,以及产流产沙量与降雨因子之间的相关性。结果表明:(1)不同郁闭度马尾松林产流产沙量均随降雨等级的增加呈逐渐增大的趋势,且暴雨下增加更为明显;(2)在中雨、大雨和暴雨3种降雨等级下,郁闭度0.2和0.8马尾松林产流产沙量均高于郁闭度0.4和0.6,且郁闭度0.4和0.6马尾松林产流产沙量随降雨等级增加变化较小;(3)在自然降雨梯度下,不同郁闭度马尾松林产流产沙与降雨量和降雨侵蚀力显著相关(P<0.05);(4)逐步回归分析发现,不同郁闭度马尾松林产流回归方程的主要变量是降雨量和最大30 min雨强,而产沙回归方程的主要变量是降雨量和降雨侵蚀力。综上,马尾松林郁闭度过高或过低不利于水土保持,长汀红壤侵蚀区郁闭度0.6马尾松林防治水土流失效果最佳。

Characteristics of Soil and Water Loss Under Different Natural Rainfall Grades of Pinus Massoniana Forest with Different Canopy Density

In order to reveal the law of soil erosion of different canopy density Pinus massoniana forests in the red soil erosion area of southern China, the standard runoff plot observation method was adopted in different canopy density (0.2, 0.4, 0.6, and 0.8) Pinus massoniana forest in the Changting of Fujian Province. A rainfall gradient was constructed to analyze the variation of soil erosion with the rainfall level of different canopy density Pinus massoniana forests based on the 37 natural rainfall events observed in 2015. The correlation between runoff and sediment yield and rainfall factors was conducted. The results showed that:(1) The runoff and sediment yield of different canopy density Pinus massoniana forests increased gradually with the increase of rainfall grade, and the increase was more obvious under rainstorm condition. (2) Under three rainfall grades such as moderate rain, heavy rain, and rainstorm, the runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.2 and 0.8 were higher than that with the canopy density of 0.4 and 0.6. The runoff and sediment yield of Pinus massoniana forests with the canopy density of 0.4 and 0.6 showed less variation with the increase of rainfall grades. (3) The runoff and sediment yield of different canopy density Pinus massoniana forests were significantly correlated with rainfall and rainfall erosivity (P<0.05) under the natural rainfall gradient. (4) The stepwise regression analysis showed that the main variables of the regression equation of the runoff of Pinus massoniana forests with different canopy density are rainfall and the maximum 30 min rain intensity, while of the sediment yield regression equation are rainfall and rainfall erosivity. In summary, the higher or lower degree of canopy pine forest is not conducive to soil and water conservation, and the most effective canopy closure degree of Changting red soil erosion is 0.6 to control the soil and water erosion of Pinus massoniana forests.