| Since the 21st century,vegetation has been fully and rapidly restored in China.In 1999,the grand project of returning farmland to forest(or grass)played a vital role,hindering the deterioration of the ecological environment.The Loess Plateau is rich in resources but still has the most serious soil erosion in the world.As the environment deteriorates,the structure and function of the ecosystem are destroyed.By studying the service functions of the Loess Plateau ecosystem and the changes in vegetation,the ecological construction structure is optimized to benefit mankind.Based on remote sensing image data,basic geographic information data and statistical data,this study analyzes the vegetation changes since the implementation of the project of returning farmland to forests in the Loess Plateau.Based on the field survey data and model parameter empirical values,the In VEST model was used to evaluate the loess from 1980 to 2015.Plateau water production,soil retention and carbon sequestration.Based on the analysis of ArcGIS,this paper obtains the spatiotemporal changes of ecosystem service functions of different land use types,explores the response relationship of service functions to vegetation restoration through the spatiotemporal changes of service functions under different climatic conditions,different types of erosion types,and different vegetation conditions,and proposes feasible Sexual advice.The main research results of this article are as follows:(1)Analyzed the vegetation restoration status of the Loess Plateau from 1980 to 2015.Based on the analysis of the land-use change and the spatio-temporal changes of NDVI in this area,firstly,through the characteristics of the land use change on the Loess Plateau and the land use transfer matrix,we can see that in 2000 In the past,the change from grassland to unused land and cultivated land was the main one.After 2000,the main change was from cultivated land to forest land.From 2000 to 2010,due to the impact of the conversion of farmland to forest and grassland,a large amount of forest land increased,mainly from cultivated land and grassland.In particular,the conversion area of cultivated land is the largest;the conversion range of grassland to forest land increased significantly from 2010 to 2015;the construction land continued to expand after 2000.Then use univariate linear regression to analyze the overall change trend of vegetation coverage and precipitation during the study period.It can be seen that NDVI has grown steadily in the small fluctuations during the study period,and the vegetation has improved;it can be seen that the floating trend of NDVI change is consistent with the precipitation,and it can be predicted that the vegetation coverage of the Loess Plateau will continue to change with precipitation after 2018.The range is steadily increasing,but due to the influence of soil water content,a coverage threshold may appear.Next,the NDVI variability and the variability grade of the Loess Plateau were analyzed.The weak variability was mainly distributed in Henan,central and eastern Shanxi,and Guanzhong,with a variation area of 29.71%;the medium variability was mainly distributed in Inner Mongolia,Ningxia,Gansu,and northern Shaanxi.The area of variation accounts for 70.28%;only Shaanxi Yulin and western Inner Mongolia have a small range of strong variation,accounting for only 0.01%of the total area.Based on the analysis of the variation coefficients of different erosion types in the Loess Plateau,the NDVI medium and strong variations are mainly hilly and gully areas,wind and sand areas,and high and gully areas.Since the implementation of returning farmland to forest and grassland,the center of gravity of NDVI on the Loess Plateau has shown a trend of changing from southwest to northeast.From 2015 to 2018,the transfer distance was up to 15.78 kilometers.Combined with the distribution of variation levels,since 2000,the change of the center of gravity of the vegetation on the Loess Plateau has shown a tendency to move to areas with more serious water and soil erosion,such as wind and sand areas and hilly and gully areas.(2)The water production service,soil conservation service and carbon sequestration service function level and their changes in the Loess Plateau from 1980 to 2015 were evaluated.The annual water production of the Loess Plateau in the southeast is far greater than that in the northwest,and the water production of cultivated land The most;among them,the average water production in 1990 was the highest in five years,reaching 122.421mm.From the average of water production,there was no obvious change trend overall.The spatial distribution characteristics of soil retention also showed the overall trend of high in the southeast and low in the northwest.Forest land,cultivated land and grassland have the most soil retention.From the average value,the overall amount of soil conservation shows an increasing trend,especially after 2000,the average amount of soil conservation for different land use types is 184.86 tons/ha,210.65 tons/ha,and 295.82 tons/ha;the soil and grass ecosystem soil retention It shows a relatively obvious growth trend,among which forest land is the most prominent.The function of carbon sequestration service is the forest and grass ecosystem.The total area of forest and grass increases most significantly in 2000～2010.Although the total area of forest and grass decreases in 2010～2015,the total amount of carbon sequestration has increased significantly,mainly due to the The area of annual grassland to forest land conversion is large.(3)Revealed the response relationship of the ecosystem function of the Loess Plateau to vegetation restoration and put forward feasibility suggestions;firstly,the service function level of different erosion type areas was evaluated.It can be understood that except for the valley plain area,the amount of soil conservation is After 2000,there was an obvious growth trend.The high-gully areas increased the most,and the sand-sand areas increased the most,reaching 113%.Except for river valleys and plains,areas with large variability in vegetation coverage and soil retention and carbon sequestration services also improved more;Not all vegetation-rich areas have correspondingly rich water production.In hilly forest areas,forest vegetation covers a high carbon sequestration base,and the valley plain area as the main grain production area may result in soil conservation and carbon sequestration levels due to farming systems and urbanization.At the same time,the land use changes in different erosion zones from 1980 to 2015 were evaluated.By comparison,the total area of forest and grass in each zone of the Loess Plateau determines the level of soil conservation service function,and the proportion of fore st land area determines the level of carbon sequestration service function.Based on the pixel scale,the correlation between water production and soil retention and NDVI was analyzed using Pearson correlation coefficients,and a linear regression analysis was performed to find that the water and soil conservation services in the Loess Plateau all showed a significant increase trend with the increase of NDVI;the water production at NDVI was 0.7 It peaks at the left and right,and then no longer increases or even declinesmainly because when the vegetation coverage reaches a certain threshold,the water production is generally water-consuming;the soil retention amount has a tendency to increase significantly when the NDVI value is close to 0.8.In summary,the increase in forest and grass significantly affects soil retention and carbon sequestration,and the response of soil retention and carbon sequ estration to forest land is higher than that of grassland,resulting in the total amount of soil and soil carbon sequestration during theconversion of grassland area the forestland.Significantly increased;precipitation as a climatic factor directly affects water production,and in directly improves soil conservation and carbon sequestration functions by increasing vegetation coverage.The impact of human factors on service functions is mainly the improvement of service functions through ecological construction such as returning farmland to forests and grasslands,and the second is the weakening effect of human activities such as mining,urban construction,and forest vegetation destruction.Afforestation and urbanization relationship to maximize service function benefits. |
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