| Under the background of climate warming,the cultivated land area of Sanjiang Plain increased significantly,especially the proportion of paddy fields increased rapidly,and have become an important commodity grain base.Net Primary Productivity of vegetation as an important factor in Eco-environmental Assessment,mainly affected by climate,soil and human activities.As an important type of land use and cover,cultivated land plays an important role in productivity change,especially in Sanjiang Plain,where cultivated land is the main land use type.Therefore,the analysis of cultivated land use change and its impact on farmland productivity in Sanjiang Plain provides the basis for ensuring food security,regulating ecological service function and making agricultural policies.This paper uses spatial data of cultivated land in 2000,2005,2010 and 2015 to analyze the change of cultivated land quantity and scale,the change of internal structure,the degree and rate of change and the regional difference.Using the spatial data of net primary productivity from 2000 to2015,the interannual variation and spatial distribution characteristics in the study area are analyzed,and the trend of future change is forecasted.Furthermore,using spatial data of cultivated land and NPP data,the characteristics and trends of farmland productivity of different cultivated land use types were analyzed,and the influence of the change of cultivated land area and internal structure on farmland productivity was analyzed.The main contents and conclusions of this paper are as follows:(1)Based on the spatial data of cultivated land from 2000 to 2015 in Sanjiang Plain,using GIS spatial model and mathematical statistical method,the temporal and spatial changes of cultivated land distribution pattern were analyzed.It was found that the cultivated land in Sanjiang Plain was mainly distributed in the northern and central regions of the study area from 2000 to2015,with a slight increase in area.The internal structure of cultivated was quickly adjusted,and the change of paddy field is more remarkable than that of dry land and cultivated land,and the main performance is that the proportion of paddy field rises rapidly.The average annual change rates of cultivated land,paddy field and dry land were 0.14%,8027%and-2.00%,In recent 15years,the area of dry land transformed into paddy field has reached 1446km~2,accounting for84.22%of the total area of cultivated land change.It is shown that climate warming and the demand of economic development result in the change of cultivated land structure in Sanjiang Plain since 2000,that is,the area of paddy field expands rapidly,and the area of dryland decreases,especially in the northeast area of Sanjiang Plain.(2)Based on the model simulation of NPP in Sanjiang Plain,the average,maximum,standard deviation and coefficient of variation of NPP in Sanjiang Plain were statistically analyzed.It was found that the maximum,average,standard deviation and coefficient of variation of NPP in Sanjiang Plain in recent 15 years showed a fluctuating increasing trend.The mean values are obviously different in different regions,which are higher in the middle north,lower in the northeast,northwest and southwest.In the central region,because of the flat terrain,abundant precipitation,complex vegetation types,favorable water and heat conditions for vegetation growth.The land use types in the northwest and southwest are mostly woodland,and the NPP mean value is low due to the single vegetation type.By calculating the Hurst index of NPP in the study area and predicting its future variation trend,it is found that the annual correlation of NPP values in most areas of Sanjiang Plain is weak,and the future development trend of NPP is difficult to predict by using NPP data in previous years.(3)The spatial data of cultivated land and the data of NPP were superimposed to analyze the productivity of different types of cultivated land,and the level of farmland productivity was classified by anomaly,in order to analyze the influence of the change of cultivated land area on the level of farmland productivity.In recent 15 years,the total NPP of farmland and paddy field in Sanjiang Plain increased,while the total NPP of dryland decreased.The average value of farmland NPP increased,and the productivity of paddy field was higher than that of dryland productivity.The change of cultivated land area leads to different trends of farmland productivity in different grades.With the change of cultivated land area,the area of low yield field decreased,the area of middle yield field first increased and then decreased,and the area of high yield field increased;with the increase of paddy field area,the area of low,medium and high yield paddy field all increased,but the proportion of low yield paddy field increased.The proportion of middle yield paddy field increased first and then decreased,while that of high yield paddy field decreased.With the decrease of dry land area,the low,middle dry area reduction,high-yield area volatility of growth,the proportion of high-yield,the proportion has been higher than the proportion of low yield dryland,and showed an increasing trend,while the low yield dryland area proportion was lowest,and showed a decreasing trend.The results show that the productive capacity of cultivated land and dryland in Sanjiang Plain is increasing generally,but in the process of dry-water reform,the main source of paddy field is low-yield dryland,which leads to the increase of low-yield paddy field area,and with the improvement of infrastructure,Dry land production is also increasing.(4)Analyzed the correlation between cultivated land use change and its productivity change by Using the spatial analysis method based on pixel.It is found that the cultivated land use change and NPP change have certain correlation in Sanjiang Plain,in which the new cultivated land area is mainly positively correlated with NPP.There is a negative correlation between the reduction of cultivated land area.Analyzed the regional productivity change trend of the two types of internal structure transformation,it is found that the productivity changes in the two different conversion regions of dry-to-paddy region and paddy-to-dry region are both showing an increasing trend.The change of regional productivity of dry-to-paddy region is slower than that of paddy-to-dry region.The farmland productivity fluctuated greatly in 2008-2011,but increased obviously after that,indicating that the farmland productivity was very unstable during the implementation of land regulation project in this region,but the productivity increased obviously after implementation.Analyzed the effect of changes in the internal structure of cultivated land on NPP,it was found that the productivity increased with the increase of paddy field area,but increased with the decrease of dryland area. |
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