| Soil erosion is one of the major environmental problems of common concern in today’s world,it has become an important factor in the threat of ecological security of our country. Prevention of soil erosion is the key to changing the production and development of human irrational manner, and degraded ecosystem restoration and reconstruction. Hilly area in Sichuan as an important ecological barrier upstream of the Yangtze River,in the area has been created a large number of pure Cupressus funebris forest in the Yangtze River shelterbelt construction projects. Due to the composition of a single species, planting density is too large, and management lags behind, it resulting in existing forest stands more become inefficient, and soil water conservation features severely degraded. Therefore, this study in 2012 used to typical Cupressus funebris inefficient forest restructuring and functional improvement.on the territory of Deyang City Jingyang district.By used thinning respectively, artificial gaps (promotion of natural regeneration and artificial update), horizontal band cut afforestation (introduced species native broadleaved species and economic pepper) and other types of transformation model, with no treatment for the control of cedar forests.By setting artificial runoff field in each treatment, the cedar forest transformation of the initial runoff, soil erosion and soil nutrient loss research studied the situation, to seek the optimum mode to enhance the eco-efficiency transformation of woodland. The results showed that:1. Each mode runoff is basically in line with rule of Model Ⅲ>Model Ⅰ>Model Ⅳ>Model Ⅱ>Model Ⅴ>Model VU>Model VI. While each mode soil sediment erosion comply the rule of Model Ⅰ>Model Ⅲ>Model Ⅳ>Model Ⅱ>Model Ⅴ>Model Ⅶ>Model Ⅵ. Slope is the primary factor affecting soil and water conservation, runoff and sediment erosion in the average slope of 5°pepper forest and are much smaller than the average for the other five plots slope of 30°. Runoff Losses law compared to sediment erosion is consistent with the law, Runoff losses law is consistent with compared to sediment erosion law, Tending and Thinning (erosion sediment 354t/km2), Plantation gap(natural regeneration) (annual runoff 330.7mm) are the largest soil and water loss modes. In addition, Broadband afforestation also came in before the control area, the Plantation gap(artificial promote) transformation effect is the best than the other modes.2. Our study found that the nutrient loss law is,in each transformation model mode, Potassium have had the most serious amount loss,followed by Nitrogen and Phosphorus have had the least amount of loss. The amount of Total N, P, K and Available N, P, K loss rule is:Model Ⅰ>Model Ⅲ>Model Ⅳ>Model Ⅱ>Model Ⅴ>Model Ⅶ>Model Ⅵ.,which is fully consistent with the laws of the amount of sediment erosion. A closer study found that, loss nutrient concentrations by sediment carried are much greater than runoff carried.For example,in the same mode, Available K content in the sediment can be up to 30 times (Mode Ⅰ) in runoff, while total K can reach 2653 times (Mode Ⅳ). It just explains why both the law of consistency. In a similar interval slope from Model V to I, Model V has the best maintaining fertilizer effect and the loss of the least nutrients loss amounts. The nutrient loss amount of total of N, P, K and available N, P, K in it had decreased 21.8-22.9% compared with control ground (Model Ⅱ),compared to the the largest nutrient loss area(Model Ⅰ), Model V also had decreased about 81.2%-82.7%. In addition, cells of different slope, nutrient concentration gap from runoff carried and sediment carried are not the same. With available K, for example,compared Model Ⅱ to Ⅲ,both of runoff and sediment carried nutrient concentration difference are about 17 times,while the concentration difference between Model VI and Ⅶ are approximately 8.7 times, there is a significant difference between the two.There are seasonal dynamics change of Full-N, P, K nutrient loss, its trends remained the same with the annual rainfall trend, and the loss of soil nutrients and rainfall, especially once the intensity of rainfall was significantly positively related relationships. From the distribution of rainfall is August-November total rainfall of 204.7mm, April-July total rainfall of 211mm, a difference of about 3%.But former stage in the cell Ⅰ, Ⅲ, Ⅳ, Ⅴof Full-N, P, K loss accounted for 53%,61%,57% of the annual amount of the loss amount, respectively,which is a Total-N, P, K loss amount accounted for 40%,44%,36%,of annual turnover in latter stage amount, while the control cell(Model Ⅱ) former accounted for 48% and the latter for 49%. This suggests that, in addition to the factors and growth patterns of rainfall for plants, but also due to the different reconstruction methods, early transformation of the forest district on soil N, P, K had done a different type of use and the return to the soil, the ecological environment in transformation district is slowly stabilizing, early consequences in the transformation of when human disturbance are slowly eliminated, water insurance benefits is gradually reflected.3. In the study of different transformation modes reflect to different rainfall events (with Moedl Ⅰ,Ⅴ,Ⅱ, for example) found that:Comparison in September 2012 20.4mm/ h rainfall on May 2013 20.2mm/h rainfall and found that, twice rainfall is all about 20mm /h, each cell soil early moisture are about 17%, the condition can be considered consistent approximation. The total initial produce runoff time rule is Model I (Tending and Thinning)> Model II (control forest)> Model V (Artificial gap with broadleaf in), and eight months after the transformation, the three residential runoff time been extended 6-10min range, it’s the same with resulting rule of soil physical and chemical properties before and after variation, description that,with the growth of the transformation of the nature of time, soil porosity, bulk density, organic matter is being improved, the transformation of cells of each soil erosion resistance than the self is gradually strengthened.Slope sediment yield curves showed a two-stage development, the first stage can be seen as a sharp increase in slope erosion stage, the second stage can be seen as a stable slope sediment production stage. Contrast twice 20.2mm/h and 40.4mm/h rainfall in May.2013 can be found, when rainfall intensity increases at a time,the latter soil erosion peak in rainfall curve is about the maximum 9-11 times than the former curve peak (it were 77.25g/m2,88.69 g/m2,106.28 g/m2). Meanwhile, in the greater rainfall intensity, there is a bottom value range before stability yield in the slope sediment process curve, which is related to skin contact with the soil.In summary, the slope is an important factor affecting woodland soil erosion, with an average slope of 5°pepper forest runoff and sediment erosion are far less than the average slope of several other models of 30°. In addition, the annual rainfall and rainfall intensity in the study area was also significantly affected woodland runoff, sediment erosion and nutrient loss. After transformation la time, in addition to the artificial window (Artificial regeneration), the Thinning, artificial window (natural regeneration) afforestation and soil conservation benefits of broadband Cupressus funebris forest is poor than not treated as control. Shows that in the early Cupressus funebris forest transformation of artificial gaps and promptly update the introduction of native species to promote would get better water conservation benefits. From a long-term point of view, whether it is conducive forest ecological benefit and improve the overall service functions remains to be seen. |
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