| Returning farmland to forest and grassland in the deteriorating ecological environment under the background of China government is proposed to improve the ecological environment,the adjustment of rural industrial structure,promote regional economic development and the ecological construction project,its sustainability is always the focus of government departments and academia.In view of the lag of the economic benefits of returning farmland to forest and grassland and the lag of ecological benefits,and the differences of different regions,it is necessary to carry out the stage assessment of the project of returning farmland to forest and grassland in different regions.The southwest karst area is located in the upper reaches of the Yangtze River and the Pearl River.The irrational predatory development and the fragile ecological environment are deteriorating.Most of the forests degrade in different degrees,soil erosion is serious,and many areas are even rocky desertification.Rapid development of the overall trend has not been effectively curbed,has always been the focus of vegetation restoration and ecological management and difficulties.In order to improve the karst gradually deteriorate the ecological environment and fundamentally reverse the development trend of rocky desertification,the southwest region in 2002 launched a comprehensive project of returning farmland to forest and grassland ecological environment.This study is based on the reconstruction of demonstration base of ecological restoration and Guangxi depressions of Huanjiang Gu Zhou Karst peak in 2007(5 years)the farmland planting Zenia insignis,Toona sinensis,Castanea mollissima,Citrus reticulate,Zenia insignis + Guimu No.1 Forage,Guimu No.1 Forage and leaving land uncultivated 7 major reforestation model sample,in 2012(10 years)to conduct a comprehensive review and analysis of vegetation and soil,using the classical statistical method,comparative analysis of Karst peak cluster depression of different reforestation patterns of vegetation and soil ecological benefit and dynamic changes,mainly affected by principal component analysis method to reveal the Karst peak cluster depression reforestation the factor,with the method of canonical correlation analysis to explore the mode of returning farmland to forest and grassland vegetation and soil interaction mechanism,screened in Karst peak cluster depression reforestation model optimization.Through the conversion of cropland to forest vegetation and soil effects of early and mid grass engineering analysis for returning farmland to forest and grass project sustainability evaluation and post relevant policies to provide a scientific basis for designing,the protection of the area of returning farmland to forest and grass project sustainable development.The main conclusions are as follows:(1)The plant growth status of different cropland to forest and grassland in the study area was different.Returning farmland to forest patterns are formed tree layer,Zenia insignis + Guimu No.1 Forage with the average DBH of zeniainsignis reached 15.44 cm,the tree is as high as 12.65 m,crown 4.92 m,these indicators were significantly higher than those of other models;followed by Castanea mollissima,Zenia insignis,Citrus reticulate and Toona sinensis.Herb layer is still an important part of plant community,the average height of the leaving land uncultivated highest,was 222.21 cm,followed by Guimu No.1 Forage,were significantly higher than that of Toona sinensis,Zenia insignis and Citrus reticulate mode.(2)Reafforestation middle all patterns of species richness and Shannon index were not high,species richness ranged between 6.2~11.1,Shannon index between 1.172-2.160;Simpson index and evenness index were higher,uniformity of each mode is still in the low species distribution and low level high state.(3)Different models of community biomass in the range of 31.90~135.93 t/hm2,far higher than the initial biomass,biomass of each mode in the order of Zenia insignis + Guimu No.1 Forage,Toona sinensis,Castanea mollissima,leaving land uncultivated,Zenia insignis,Guimu No.1 Forage,Citrus reticulate,which Zenia insignis + Guimu No.1 Forage was significantly higher than that of Guimu No.1 Forage mode and Citrus reticulate pattern,significantly higher than the other 4 models.The biomass distribution patterns of different models of returning farmland to forest and grassland were different.In the 5 models of returning farmland to forest,the biomass was mainly distributed on the target tree species.In addition to the Guimu No.1 Forage mode,the biomass of the herb layer of the other 6 models was larger,and the proportion of total biomass was between 6.47%~15.81%.There was litter biomass in all models,but the proportion was small.(4)According to the vegetation effect,7 kinds of modes can be divided into 4 categories,the first category for Zenia insignis,Citrus reticulate and Toona sinensis,second kinds of Zenia insignis + Guimu No.1 Forage,third for Guimu No.1 Forage,leaving land uncultivated,fourth for Castanea mollissima.(5)Compared with the early stage,except for Castanea mollissima and Toona sinensis,the p H of other model soils had different degrees of improvement,from neutral to slightly acidic to neutral to slightly alkaline.The soil organic matter of each model showed a decrease in different range,and the differences between the models were reduced.There was no significant difference in soil nutrients between different models,especially AN and AP.(6)The effects of different models of returning farmland to forest and grassland on soil microbes were different.The MBC and MBN of the soil microbes in Toona sinensis were the highest,which was significantly higher than that of other models,and the change of soil MBP was not significant.Soil microbial population quantity and composition of different patterns and different,as in the early,returning farmland to forest soil bacterial populations were dominant,while in the other 3 models,the number of actinomycetes population proportion has an absolute advantage,the number of fungi accounted for a very small proportion.(7)7 modes of Karst peak cluster depression reforestation middle clustered into soil was significantly improved,soil type,soil type and soil improvement slowly improved hysteresis of 4 types,but the quality of the soil ecosystem of each mode has changed greatly.(8)The main factors affecting Karst fengcong depression of returning farmland to forest and grassland ecosystem is mid plant community diversity,soil organic matter,TN,AN,AK and other 8 indicators,especially the plant community diversity,thus returning mid forest and grass can be used after the stage of succession of plant species.Canonical correlation analysis showed that Karst fengcong depression reforestation in middle,different modes of physical and chemical properties,vegetation and soil vegetation and soil microbial and physicochemical properties of soil and soil microorganism of first typical variables were significant,the typical variable physicochemical characteristics of vegetation and soil in attribute tree DBH,tree canopy vegetation and soil p H value,vegetation tree crown,the average height of trees and the quantity of soil microbes,soil chemical properties,p H value,available P and the number of actinomycetes populations most affected.Based on the comprehensive analysis of 24 vegetation,soil chemistry and microbial index in the middle stage,it can be divided into the following 4 categories,the ecological effect of each type is similar,and the difference of different types is large. |
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