| China is a large country of plantation resources,but in the process of plantation management,due to long-term pure forest management or improper operating measures and other factors,the prevalence of serious loss of biodiversity,low production efficiency,ecological function is generally not high,serious soil erosion ecological security issues.The use of precious native timber tree species to transform existing low and low efficiency plantations is an important way to improve the production efficiency and ecological protection of plantations.However,in the process of artificial forest transformation,due to the use of different transformation mode or different ways of soil preparation technology,inevitably lead to the initial soil erosion and soil erosion increased the phenomenon of decline.Therefore,it is an important content to be concerned about the process and mechanism of soil erosion and the law of soil erosion and its evolution law,which is different from the different transformation and regeneration mode or land preparation method in the early stage of transformation.In this paper,the low-efficiency artificial forest of Pinus massoniana in hilly area of southern Sichuan was used as the research object,and 4 methods of setting up 5 artificial trees were established.The characteristics of runoff and sediment yield and the evolution process of the slope on the early stage of the transformation of different provenances of Pinus massoniana were studied from the aspects of water holding function of litter,soil erosion resistance and surface runoff and sediment yield.The change of soil erosion and the corresponding soil water and soil conservation function were systematically studied,and to explore the evolution rule of soil and water conservation in different landforms of low efficiency forest of Pinus massoniana,in order to provide theoretical and technical support for the transformation and renewal of local inefficient plantation and sustainable management of forest.The following results were obtained:(1)Local rainfall and more concentrated in Jun?Sep,the average annual rainfall was about 1000mm.The minimum rainfall was 1.2 mm,the minimum rainfall was 6.9 mm and the maximum rainfall was 93.8 mm.A year after the start of the runoff plot test,the runoff coefficient of each plot decreased by more than 30%,and the cutting area was even about 50%.The correlation coefficient between rainfall and surface runoff is above 0.905.(2)In the second half of 2012,the number of runoff in the runoff area exceeded that of 2013 and 2014,and the sediment rainfall decreased from about 50%to about 20%.The size of sediment concentration in 5 runoff towns was consistent with the degree of human disturbance,and the highest level of ? was the highest.Winter due to less rainfall,no sediment occurred.At the initial stage of the experiment,the erosion modulus of each runoff area is above 6000 t/km2·a,and in 2014,it was reduced to 700t/km2 · a.(3)A total of nine typical singal rainfalls were selected for the three types of rainfall,and the characteristics of runoff and sediment yield were compared under the secondary rainfall conditions.The total rainfall output was reduced by-6.44%,10.51%,20.95%,13.28%and 12.73%respectively.The total sediment yield decreased by 58.4%,56.38%and 77.72%,78.16%,79.68%.The linear relationship between rainfall and runoff was better,R2 was 0.9536,and after sedimentation's R2 was 0.4647.Indicating that the runoff size of the slope was mainly affected by rainfall,and the size of sediment production is determined by a variety of factors.The yield and sediment yield reached R2 was 0.6356 after fitting,indicating that there was a close relationship between the two factors.(4)The proportion of litter size of non-decomposed layer was CK>L30>L20>L40>QK>L10,the proportion of decomposed layer was L20>L10>L40>QK>L30>CK.Litter maximum water holding capacity of the order of L30>QK>L10>L20>L40>CK.The effective storage volume was ranked L30>QK>L10>L20>L40>CK,and the effective storage of litter was between 8.85 t/hm2 and 11.14 t/hm2.Litter layer water holding capacity and flooding time there are the following relationship:w = alnt+b,R2 were more than 0.86.Four patterns litter absorption rate is undecomposed layer>semi-decomposing layer>decomposed layer QK was a semi-decomposing layer>undecomposed layer>decomposed layer;CK was a semi-decomposing layer>decomposed layer>undecomposed layer(5)The water holding capacity of CK was the best among the six types of plots.The maximum water holding capacity and field water holding capacity of surface soil(0?20cm)were better than those in the second layer(20?40cm).The soil total porosity and capillary porosity were lower than those of CK plots,and the non-capillary porosity was higher than that of CK.The porosity of the topsoil is greater than that of the second layer,and the non-capillary porosity is opposite.The surface soil bulk density ranking was L30-1(1.50g/cm3)>L40-1(1.37g/cm3)>L20-1(1.36g/cm3)>L10-1(1.34g/cm3)>CK-1,QK-1(1.33g/cm3),and the second layer bulk density ranking was L20-2(1.58g/cm3)>L10-2,QK-2(1.50g/cm3)>L30-2(1.45g/cm3)>CK-2(1.40g/cm3)>L40-2(1.39 g/cm3).With the transformation time,the ratio of 2?5mm particle aggregated with diameter less than 30m showed an increasing trend,and the proportion of 0.5?1mm,and 1?2mm aggregated decreased.The proportion of water-stable aggregates of each particle size decreased with time.The soil average weight diameter(MWD)of CK plots was significantly higher than that of other plots.The MWD of 0?20cm soil layer decreased with the increase of the gap.The difference between MWD was not significant.In addition to L10 sample 0?20cm soil aggregate agglomeration rate decreased slightly,the remaining samples of the indicators have increased to varying degrees.Compared with CK,the content of soil organic matter in the surface of the different transformation mode was significantly lower,but the change of the lower layer was not significant.From the model of transformation,the clear cutting mode was lower than that of the gap.The content of soil organic matter in different types of soils was very different,while the difference of organic carbon content between CK and L10 and L40 and QK was not significant.(6)The effects of maximum soil water holding capacity,soil total porosity,capillary porosity,non-capillary porosity,bulk density,average weight diameter,agglomeration rate,erasable factor K and organic carbon content were selected.The law yields two principal component regression equations:F1=0.01X1+0.127X2+0.182X3-0.245X4+0.114X5+0.136X6-0.179X7-0.178X8+0.111X9;F2=0.346X1+0.068X2-0.071X3+0.408X4-0.502X5+0.067X6+0.044X7+0.041X8+0.092X9?And the comprehensive evaluation index of soil and water conservation function is calculated:F = 0.797Fi + 0.203F2.The results showed that the soil and water conservation functions of L10 and L20 were not much better than those of L30,L40 and QK plots.The comprehensive analysis showed that the surface runoff and sediment yield were obviously decreased with the restoration of vegetation in the early stage of plantation.But the soil water holding capacity,water stable aggregates,organic matter content and soil corrosion resistance all decreased,and increased with the increase of interference degree,which accorded with the objective law of the early stage of forest transformation,indicating that the appropriate transformation mode And afforestation method is an important measure to reduce soil erosion and reduce soil erosion.Different transformation mode will be with the growth of trees and forest ecosystems self-improvement,the soil and water conservation benefits will be significantly improved.However,due to the short time of this study,the long-term evolution of soil and water conservation function of the gap can be further studied in the future. |
PDF Full Text Request