Influence Of Vegetation Restoration On Soil Anti-erodibility In Haifeng Karst Gabin Basin,East Yunnan

In order to explore the difference of soil erosion resistance under Pinus yunnanensis vegetation community on rocky desertification slope in karst depression basin of eastern Yunnan,the synergistic relationship between different types of Pinus yunnanensis restoration communities and soil was studied.In this paper,soil anti-erodibility and erosion resistance and some physicochemical properties of soil under five different vegetation types of natural secondary forest of Pinus yunnanensis,artificial pure forest of Pinus yunnanensis,artificial mixed forest of Pinus yunnanensis,primary forest of Castanopsis orthacantha and Lithocarpus dealbatus and shrub of Myrsine africanna were discussed.the effects of soil physicochemical properties and plant roots on soil erosion resistance were analyzed by grey correlation degree method.Comprehensive evaluation of soil erosion performance of five vegetation communities using PCA and coupled relationship model.The main conclusion obtained are as follows:（1）Soil physicochemical properties differed under different vegetation communities.On the whole,the physical indexes such as soil bulk,total porosity and large particle agglomerate content of Castanopsis orthacantha and Lithocarpus dealbatus under native forest were better than those under the other four planted communities.Among the three kinds of Pinus yunnanensis forest,the soil physical properties and SOC of Pinus yunnanensis mixed forest are better than those of natural secondary forest and artificial pure forest.However,soil organic carbon in the understory of all three species of Pinus yunnanensis is lower than that in primary forest and scrub.SOC,TN,TP and other nutrients under the five planting communities show phenological aggregation.The results of the wet and dry sieve of soil agglomerates show that large particle agglomerates are preferentially eroded under rainfall conditions.Integrating the degree of agglomerate damage and the variation characteristics of MWD and GMD of agglomerates under dry and wet sieves,it was found that the native forest soils were the most stable and resisted erosion,while the soils under three types of Pinus yunnanensis were less stable and susceptible to soil erosion.The physicochemical properties of the soil did not boost gradually with the positive succession of the vegetation community.（2）There were differences in soil erosion resistance under different vegetation communities.Among the three kinds of Pinus yunnanensis forest soils,artificial pure forest of Pinus yunnanensis has the lowest anti-erodibility index,reaching 27%.The anti-erodibility index of the Castanopsis orthacantha and Lithocarpus dealbatus primary forest was the largest,followed by Myrsine africanna shrub,reaching 73.67%and 72.67%,respectively.The anti-erosion performance index of different soil layers under the same vegetation type showed that except for Pinus yunnanensis plantation pure forest,and the soil resistance index of 0-20cm soil layer under the other four vegetation types was higher than that of 20-40cm soil layer.In a word,the more deeper the soil layer is,the more weaker the soil resistance performance is.With longer submersion time,the soil anti-erodibility index decreases and the anti-erosion performance becomes weaker.The function fit of the two is best fitted by a cubic polynomial function.SOC,TN,clay grain,>5 mm water-stable aggregates,total porosity,TP,chalk grain,>0.25 mm water-stable aggregates,sand grain,>5 mm air-dry aggregates,soil bulk weight,>0.25 mm air-dry aggregates,all 12 soil physicochemical indexes have strong correlation with soil erosion resistance index,among which SOC,TN,clay grain,>5 mm water-stable aggregates have more influence on soil erosion resistance.（3）Due to the heterogeneity of vegetation community types and subvegetation microhabitats,soil impact resistance varies among vegetation communities and among microhabitats of the same vegetation community.Under the soil surface microhabitat,the soil anti-scour coefficient is as follows:Castanopsis orthacantha and Lithocarpus dealbatus primary forest(8.36 L·min·g^-1)>natural secondary forest of Pinus yunnanensis(6.01 L·min·g^-1)>artificial mixed forest of Pinus yunnanensis(5.91 L·min·g^-1)>Myrsine africanna shrub(5.32 L·min·g^-1)>artificial pure forest of Pinus yunnanensis(2.56 L·min·g^-1).The soil resistance coefficients in the small habitat of stone gully were ranked as follows:artificial mixed forest of Pinus yunnanensis(3.71 L·min·g^-1)>natural secondary forest of Pinus yunnanensis(3.66 L·min·g^-1)>artificial pure forest of Pinus yunnanensis(1.5 L·min·g^-1).Comparing the soil resistance coefficients of different microhabitat types under the same vegetation type,it was found that the soil resistance coefficients within the soil surface microhabitat were higher than those in the stone gully microhabitat.There is a strong correlation between Soil bulk weight,total porosity,capillary porosity,soil saturated hydraulic conductivity（permeability coefficient）,clay,silt,water-stable aggregates,SOC and soil impact coefficient,which has a great influence on soil impact resistance.The degree of influence of different root system characteristics indicators on soil impact resistance varies,with small plant roots（2-5 mm）having the greatest influence on soil impact resistance coefficients,and plant roots having a higher degree of influence on>5 mm water-stable agglomerates than on>0.25 mm water-stable agglomerates.（4）The mathematical function of soil erosion resistance was obtained by PCA as Y=0.506Y1+0.251Y2+0.142Y3+0.101Y4.The strength of soil erosion resistance was:Castanopsis orthacantha and Lithocarpus dealbatus primary forest（2.013）>Myrsine africanna shrub（0.517）>artificial mixed forest of Pinus yunnanensis（0.299）>natural secondary forest of Pinus yunnanensis（-1.06）>artificial pure forest of Pinus yunnanensis（-1.699）.The results of the coupling degree model between soil anti-erosion performance index and soil physicochemical properties:artificial mixed forest of Pinus yunnanensis（0.730）>Castanopsis orthacantha and Lithocarpus dealbatus primary forest（0.704）>natural secondary forest of Pinus yunnanensis（0.670）>artificial pure forest of Pinus yunnanensis（0.660）>Myrsine africanna shrub（0.637）.Integrating the results of PCA and coupling degree model,it is found that the improvement effect of Castanopsis orthacantha and Lithocarpus dealbatus primary forest on soil is still higher and the soil erosion resistance is stronger;the Myrsine africanna shrub is second only to native forest,and the coupling coordination between soil erosion resistance index and soil physicochemical index is weaker;among the three kinds of Pinus yunnanensis forest,the erosion resistance of artificial mixed forest of Pinus yunnanensis is better and the erosion degree is lower;The erosion resistance of artificial pure forest of Pinus yunnanensis is the worst.