Study On Soil Particles Fractal Characteristics And Hydro-Ecological Features Of Four Vegetation Types In Mountain Tai Yaoxiang Small Watershed

The environmental problems caused by soil erosion are still one of the main environmental problems in China and the main factors restricting the sustainable development of China's social economy.National key area for soil and water loss control of Mountain Tai and Mountain Yimeng?Taiyi Mountain?is a typical area of the rocky mountainous area in northern China,and Quercus acutissima Carruth.?QAC?,Pinus densiflora Sieb.et Zucc.?PDS?,Robinia pseudoacacia Linn.?RPL?and their mixed forests are important tree species for afforestation of soil and water conservation.It has played an important role in controlling soil erosion,improving soil and protecting ecological environment.In this paper,the soil of QAC forest,PDS forest,RPL forest and Quercus acutissima Carruth.Mixed Pinus densiflora Sieb.et Zucc.forest?QAC×PDS?were selected in the Taiyi Mountain study area.The soil particle composition,soil physicochemical properties,litter water-holding characteristics,soil infiltration and water-holding properties were systematically studied by field test and laboratory analysis.The relationships between the fractal characteristics of four vegetation types soil particles and soil properties were analyzed by using fractal theory.Based on the theory and method of hierarchical analysis,the soil hydro-ecological features of the four vegetation types were comprehensively evaluated.The results indicate that:?1?The difference of soil particle composition,fractal parameters under four vegetation types varied greatly in Yaoxiang small watershed.The soil of clay,silt content and fractal parameters followed a consistent sort,QAC×PDS mixed forest>RPL forest>QAC forest>PDS forest,they decreased with the increasing soil depth;soil's Rényi spectrum was typical of anti-S-shaped decreasing function,and fractal parameters followed a identical rule capacity dimension?D₀?>information dimension?D₁?>correlation dimension?D₂?;single-fractal parameter?D?showed significant positive correlation with the clay and silt content,showed significant negatively correlated with sand content;D₀ showed significant positive correlation with the clay content,showed positive correlated with silt content,showed negatively correlated with sand content.?2?Four vegetation types had better effect of improving soil physicochemical properties,and the difference was significant in Yaoxiang small watershed.The soil bulk density of QAC×PDS mixed forest was lowest,the soil total porosity of QAC×PDS mixed forest was highest,and RPL forest,QAC forest,PDS forest came second;the soil of total carbon?C?,total nitrogen?N?followed a consistent rule,RPL forest>QAC×PDS mixed forest>QAC forest>PDS forest,they decreased with the increasing soil depth.?3?The fractal parameters of soil particle had a good correlation with soil property indexs of four vegetation types in Yaoxiang small watershed.Soil bulk density showed negatively correlated with soil fractal parameters,showed significant negatively correlated with D,D₁,showed negatively correlated with D₀,D₂;soil total porosity,capillary porosity showed positive correlated with soil fractal parameters,showed significant positive correlation with D₀,showed positive correlation with D,D₁.Soil C,N,total phosphorus?P?showed positive correlation with soil fractal parameters?besides D₁/D₀?.Studies had shown soil Particle fractal parameter was one of the important index to evaluate soil quality,and can well represent the changes of soil structure and properties.?4?The water-holding performance of four vegetation types litter layer and soil layer was remarkable in Yaoxiang small watershed.The thickness,accumulation,maximum water-holding rate?amount?and effective water-holding rate?amount?showed that:QAC forest was highest,RPL forest was lowest,the semi-decomposed layer of water-holding capacity was significantly higher than the undecomposed layer.In 0⁴0 cm soil layer,the effective water-holding capacity and capillary water-holding capacity of QAC×PDS mixed forest was highest,PDS forest was lowest,they decreased with the increasing soil depth.The soil infiltration rate of four vegetation types reached the maximum within the first 5 minutes,with the increase of infiltration time,the infiltration rate decreases and finally reaches the stable infiltration state,the steady permeability rate was between 2.57 and 3.88mm·min^-1,sort of infiltration performance was QAC×PDS forest>RPL forest>QAC forest>PDS forest.?5?Using analytic hierarchy process to comprehensively evaluate the hydro-ecological feature of four vegetation types in Yaoxiang small watershed,it was concluded that:The comprehensive evaluation results of hydro-ecological features of litter layer was QAC forest>QAC×PDS mixed forest>PDS forest>RPL forest.The comprehensive evaluation results of hydro-ecological features of soil layer was QAC×PDS mixed forest>RPL forest>QAC forest>PDS forest.It was calculated that the comprehensive evaluation score of the hydro-ecological features of the four vegetation types were between 0.793⁰.960,and follows QAC×PDS mixed forest>QAC forest>RPL forest>PDS forest,the results showed that mixed forest was better than pure forest,broadleaf forest was better than coniferous forest in soil hydro-ecological features of four vegetation types in the Yaoxiang small watershed.