| As an effective means and measures for the restoration of degraded grassland ecosystems,fence enclosure has been widely used in grassland management in China.Scholars at home and abroad have done a lot of research work on the ecological restoration of grassland vegetation and soil system by fence enclosure,but the general law of its impact is still widely disputed.In this paper,through integrated analysis(Meta-analysis),137 papers on the impact of enclosure(enclosure and enclosure)on grassland vegetation and soil characteristics in China were screened from more than3000 Chinese and English literatures,and an analysis database was established.The analysis database mainly includes 8 characteristic parameters of vegetation,including aboveground biomass,underground biomass,height,coverage,density,diversity index,richness index;and 10 characteristic parameters of soil,including soil organic carbon,total Nitrogen,total potassium,total phosphorus,available nitrogen,available potassium,available phosphorus content and soil bulk density,soil water content,soil pH.Using integrated analysis methods,systematically evaluated the impact of enclosures on grassland vegetation and soil characteristics and its driving factors(grass type,climatic conditions,grazing degree before enclosure,grazing livestock types,enclosure methods and enclosure years)The main findings include:(1)The aboveground biomass,underground biomass,height,coverage,and density of grassland vegetation communities after fence enclosure were significantly higher than the corresponding indicators of free grazing land outside the fence,and their increases were 168.69%,121.28%,90.71%,77.91% and 64.05%;while the grassland vegetation diversity index and evenness index decreased significantly by19.77% and 12.75%,respectively,but its richness index increased significantly by43.47%.(2)After the enclosure of grassland fences,the organic carbon,total nitrogen,total potassium,total phosphorus,available nitrogen,available potassium,available potassium,available phosphorus content and soil water content in the soil increased significantly by 58.19%,69.72%,7.71%,and 17.7 respectively %,6.94%,47.82%,35.84% and 7.55%;soil bulk density and soil pH decreased significantly by 9.35%and 5.11%,respectively.(3)After fence enclosure of different types of grasslands,the aboveground biomass,underground biomass,coverage,height,and richness index have increased to varying degrees;the alpine meadow diversity index has decreased significantly.Enclosure is beneficial to the increase of soil nutrients in temperate grasslands,in which the contents of organic carbon,total nitrogen,total potassium,total phosphorus,available nitrogen,available potassium,and available phosphorus are significantly increased;enclosure is beneficial to the improvement of the physical properties of alpine grassland soil,including The decrease of soil bulk density and pH value and the increase of soil moisture content.(4)The impact of enclosure on grassland vegetation under different climate backgrounds is significantly different: the increase rate of vegetation indicators in humid / semi-humid areas is higher than that in arid / semi-arid areas,in whichaboveground biomass,underground biomass,coverage,height The density has been significantly increased;however,compared with arid / semi-arid areas,humid areas /semi-humid areas are not conducive to the maintenance of vegetation diversity.In terms of soil characteristics,the increase in soil organic carbon,total nitrogen,available potassium,and available phosphorus in the humid / semi-humid region is higher than that in the arid / semi-arid region;similarly,the physical characteristics of the enclosure in the humid / semi-humid region The effects of(soil bulk density,soil moisture content,soil pH)are higher than those in arid / semi-arid areas.(5)Temperature has significantly changed the impact of enclosure on grassland vegetation.Aboveground biomass,underground biomass,richness index,coverage,and height increase the most when the annual average temperature is 0-5 degrees,while the annual average temperature is greater than 5 degrees,the aboveground biomass decreased significantly.In terms of soil characteristics,the contents of soil organic carbon,total nitrogen,total potassium,total phosphorus,available nitrogen,available potassium,and available phosphorus increased significantly with the increase of the annual average temperature,and the value increased when the annual average temperature was more than 5 degrees.(6)After fencing the grasslands of different grazing levels,it was found that the vegetation characteristics of the middle-grassland grasslands had a better increase effect after enclosure,compared with the light pasture and heavy pasture grasslands;The volume,height,density,coverage,richness index,and diversity index have all increased significantly.In terms of soil characteristics,enclosure has a significant increase effect on soil organic carbon,soil total nitrogen,soil total phosphorus,soil available potassium and available phosphorus content in grassland.In addition,fencing helps to increase the soil organic carbon and total nitrogen content of grazing grassland,reduce soil bulk density and pH,and the types of grazing livestock and different fencing methods before fencing also significantly affect the response of grassland soil characteristics to fencing.Compared with grazing in other seasons in summer,grazing throughout the year helps increase soil organic carbon,available nitrogen,available potassium,available phosphorus content and reduce soil bulk density.(7)The response of vegetation communities and soil characteristics to enclosures increases with the enclosure period.Specifically,the increase in aboveground biomass,underground biomass and density increases the most during the enclosure period of6-10 years;soil The contents of organic carbon,total phosphorus,available nitrogen,available potassium,and available phosphorus increased the most when the enclosure time was exceeded 10 years;the organic carbon and available nitrogen contents of the temperate grassland increased with the increase of the enclosure time,and the organic content of the alpine grassland The content of carbon and available nitrogen increased significantly when the enclosure time less than or equal to 5 years,and the effect was not significant when it exceeded 5 years.Comprehensive research results show that enclosure is an effective way to restore degraded grassland vegetation and soil nutrients,but it is not conducive to the maintenance of plant diversity.The enclosing ecological restoration effect is moresignificant in humid areas than in arid areas;it is more significant in areas with high annual average temperatures than areas with low annual average temperatures.The ecological restoration effect of enclosure on grassland vegetation shows a trend of increasing first and then decreasing with the enclosure period.The most suitable enclosure period for restoring grassland vegetation characteristics is 6 to 10 years.The above results will provide a theoretical basis for the restoration and management of degraded grasslands. |
