Ecological Effects Of Forest And Grass Measures For Soil And Water Conservation On Loess Plateau

The ecology of Loess Plateau is fragile and soil and water loss is serious.The implementation of forest and grass measures of soil and water conservation can effectively reduce soil erosion,increase soil carbon sequestration,and maintain the health and stability of the ecosystem.Since the 1990 s,with the implementation of ecological restoration strategies in the Loess Plateau,the vegetation coverage of the Loess Plateau has increased significantly,and the water and sediment in the Yellow River Basin have decreased sharply.In order to evaluate the ecological effects of forest and grass measures for soil and water conservation,a large number of slope experiments have been conducted on the effects of vegetation on sediment reduction and carbon sequestration.However,the vegetation-water-sediment relationship is generally affected by vegetation types,growth conditions,meteorology,topography and other factors.The Loess Plateau has a vast area,rich vegetation types,and significant spatial heterogeneity in climate and underlying surface conditions.The conclusions of traditional single-point experimental studies with obvious targets are difficult to objectively reveal the overall ecological effects of vegetation restoration measures on the Loess Plateau and their leading influencing factors,and the research results are limited and spatio-temporal differences.Therefore,with the forest and grass vegetation in the Loess Plateau as the main research object,Meta-analysis was selected as the main research method.Through retrieval,reading,screening and extraction,more than 200 published literatures and research reports related to slope runoff and sediment and soil organic carbon after forest and grass vegetation coverage in the Loess Plateau were collected.A total of 820 sets of runoff data,712 sets of sediment data and 1700 sets of soil organic carbon data were obtained.Integrated analysis was conducted to obtain the general rules of flow and sediment reduction and soil carbon sequestration effects of forest and grass measures on the Loess Plateau under different rainfall conditions and natural geographical conditions,explore their effect thresholds,analyze the main influencing factors of each effect,and reveal the direct,indirect and comprehensive effects of each influencing factor on flow and sediment reduction and soil carbon sequestration effects.In order to put forward the sustainable development of regional forest and grass vegetation construction suggestions.The results show that:(1)The cover of forest and grass has a significant impact on the slope flow and sediment reduction effect,and there are differences under different rainfall and physical geographical conditions.The average sediment reduction effect of forest and grass cover on the Loess Plateau was 82.60% and 88.64% respectively.The flow and sediment reduction effect under arbor forest cover was better than that under shrub,grassland and mixed forest cover,and showed a trend of first increasing and then decreasing with the increase of slope.The increase of vegetation coverage is beneficial to improve the effect of runoff and sediment reduction in the runoff plot.The sediment reduction effect under forest and grass coverage is better in the area with average annual rainfall > 550 mm,and the sediment reduction effect is better in the area with average annual rainfall of 450-550 mm.With the change of vegetation coverage and slope,the change rate of flow and sediment reduction of grassland and shrub cover was larger,while that of arbor forest and mixed forest was smaller.The effect of forest and grass measures on sediment reduction was higher in the range of 10°-20° and the range of vegetation coverage was 60%-80%.(2)The soil carbon sequestration effect was significantly enhanced by the cover of forest and grass,and there were differences under different rainfall and physical geographical conditions.The average soil carbon sequestration effect of forest and grass cover on the Loess Plateau was 64.20%.The carbon sequestration effect of forest cover was better than that of shrub and grassland cover.The soil carbon sequestration effect was better in areas with average annual rainfall of 450 ～ 550 mm.The effect of soil carbon sequestration first increased and then decreased with the growth of vegetation restoration years,and the overall trend was increasing.With the increase of soil depth,soil carbon sequestration effect gradually decreased and finally stabilized.About 30 years after vegetation construction,soil carbon sequestration effect was better.When the soil depth exceeds 60 cm,the soil carbon sequestration effect tends to be stable and the response degree to vegetation is low.(3)Rainfall factors,topographic factors,vegetation factors and geographical location factors will have direct and indirect effects on flow reduction and sediment reduction and soil carbon sequestration effects of forest and grass measures.Rainfall intensity is the main influencing factor of the downflow effect,and slope and vegetation coverage can indirectly promote the downflow effect.Precipitation is the main influencing factor of sediment reduction effect,and slope and vegetation coverage can indirectly promote sediment reduction effect.The years of vegetation restoration are the main influencing factors of soil carbon sequestration effect,and soil depth can indirectly inhibit soil carbon sequestration effect.In the future,the construction of forest and grass vegetation on Loess Plateau should take local conditions as the central idea,rationally allocate forest and grass vegetation,give full play to the ecological effect of forest and grass vegetation,and achieve the goal of sustainable development.