Study On Soil Erosion Regularity And Control Measures Under Masson Pine Forest In Red Soil Region Of Southern China

Soil erosion was serious in red soil region of southern China and it had seriously hampered the regional development of socio-economic and ecological environment. Increasing vegetation coverage could effectively mitigate the impact of rainfall on soil erosion on slope, so it has a good effect on soil and water conservation. Masson pine(Pinus massoniana)is the main vegetation restoration tree species used for soil and water conservation in red soil region of southern China, howerer, after large-scale aerial seeding, moderate even intense soil erosion still exist on forest floor which soil erosion modulus was more than 2500t/(km2·a). To improve and promote ecological restoration of degraded Masson pine forest and sustainable development of economic society in the area, five runoff plots were set up at Changting county in Fujian province including one bare plot and other four plots with different plants(pure Masson pine forest, Masson pine and grass, Masson pine and shrub, Masson pine, grass, and shrub) to study characteristics of raindrops inside and outside forest, soil and water loss process and the optimal control measure on soil erosion on forest floor by the use of runoff plots method under natural rainfall condition which was observed from May to June in 2014. The findings were as follows:(1)Raindrops inside forest were larger in number and distribution range than that outside forest. The number of raindrops inside forest was 19.5% larger than that outside forest. Raindrop size distribution inside forest ranged from 0.35 to 6.08 mm and raindrop size distribution outside forest ranged from 0.59 to 5.71 mm. Raindrop size distribution inside and outside Masson pine were fit for the function which Best came up with, volume ratio distribution of raindrops inside forest was bimodal curve while volume ratio distribution of raindrops outside forest was unimodal curve. The cumulative volume ratio distribution of raindrops inside and outside forest showed a similar S-type.(2)The rainfall intensity had an important impact on characteristics of raindrops, the function between median diameter or kinetic energy of raindrops inside and outside forest and rainfall intensity showed power. When the rainfall intensity was smaller than 0.20mm/min, the kinetic energy inside forest was larger than that outside forest, when rainfall intensity was larger than 0.20mm/min, the kinetic energy outside forest was greater than that inside forest, Soil erosion amount inside and outside forest increased with kinetic energy increasing.(3)Rainfall was redistributed after Masson pine, the ratio of rainfall inside forest, stem flow, canopy interception to total rainfall was 69.37%,1.53% and 29.10% respectively. There was a significant positive linear correlation between rainfall inside and outside forest, but the correlation between rainfall inside forest and rainfall intensity and duration was bad. The relationship between stem flow and rainfall showed quadratic equation. Rainfall amount and rainfall intensity had an obvious influence on crown interception, but rainfall duration had little effect on canopy interception.(4)In the natural rainfall conditions, runoff and sediment yield processes had a large volatility, but the process between runoff and sediment yield was similar. Sediment production process can be divided into three stages: development period, active period and stable period. During the development period, the runoff amount was little, sediment yield and its rate was relatively slow. During the active period, the runoff amount increased, sediment yield and its rate significantly increased too. During the stable period, sediment yield and its rate gradually decreased and stabilized with rainfall ending.(5)In the natural rainfall conditions, runoff and sediment yield of bare plot was the largest, and decreased from pure forest plot, tree-shrub plot, tree-grass plot to tree-shrub-grass plot.The runoff and sediment yield increased with rainfall intensity increasing. Under the condition of high rainfall intensity, the soil erosion modulus of bare plot, pure forest plot, tree-shrub plot, tree-grass plot and tree-shrub-grass plot were 174.780 t/(km2·h), 80.346 t/(km2·h), 27.411 t/(km2·h), 19.761 t/(km2·h) and 12.816 t/(km2·h) respectively. Compared with bare plot, the average ratio of runoff reduction of tree-shrub-grass plot was 77.6% as well as the average ratio of sediment reduction was 99.3%, its average ratio of runoff reduction was 29.9%, 5.9% and 12.6% higher than that of pure forest plot, tree-grass plot and tree-shrub plot respectively, its average ratio of sediment reduction was 21.5%, 2.9%,5.2% higher than that of pure forest plot, tree-grass plot and tree-shrub plot respectively.