Temporal And Spatial Dynamics Of Vegetation Net Primary Productivity And Its Climate Driving Factors Analysis In The Loess Plateau Of China

Net Primary Production(NPP)of vegetation is an important part of the carbon flux of terrestrial ecosystems,which is the result of the joint effect of the plant's own physiological characteristics and the external environment.Studying its temporal and spatial characteristics and climate driving factors can provide a scientific basis for tackling global climate and environmental changes.Based on meteorological raster data,MOD17A3 NPP data,land use data,and provincial zoning data from 2000 to 2015,this study analyzed the temporal and spatial characteristics of climate core factors using linear regression in the Loess Plateau.The vegetation NPP distribution characteristics and changing trends were discussed using piecewise linear regression and coefficient of variation analysis,and the vegetation NPP change characteristics were discussed from the perspectives of administrative divisions,vegetation types,and value ranges.The Pearson correlation analysis and generalized gradient regression model were used to analyze the impact of climate change on vegetation NPP,and the trend of temperature gradients driving factors of vegetation NPP were explored according to vegetation Types.The main The main results were presented as following:(1)The change characteristics of various meteorological indicators in the Loess Plateau from 2000 to 2015 are clarified.The annual maximum temperature and annual minimum temperature showed a downward trend,while the annual average temperature and precipitation indicators both showed an upward trend.The spatial distribution of annual average temperature were similar to the annual minimum temperature,showing a spatial distribution pattern of high in the southeast and low in the north and west.The annual mean temperature in the central part of the Loess Plateau showed a decreasing trend,while that in the surrounding area showed an increasing trend.The annual minimum temperature in the southern part of the Loess Plateau showed a downward trend,while the northern part of the Loess Plateau showed an upward trend.The difference in altitude resulted in the lowest annual maximum temperature in the western part of the Loess Plateau and higher in the northeastern part.The annual maximum temperature increased significantly in the eastern part of the Loess Plateau and decreased in the western part.The annual cumulative precipitation,annual effective precipitation days,and annual heavy precipitation all decreased from southeast to northwest.The spatial variation trend of the number of effective annual precipitation days were quite different,with increasing areas and decreasing areas alternately distributed.The area of annual heavy precipitation decreased the most,which were mainly concentrated in the southeastern part of the Loess Plateau.(2)The characteristics of vegetation NPP change in the Loess Plateau from 2000 to 2015are clarified.The vegetation NPP of the Loess Plateau showed an overall growth trend with the growth rate firstly fast and then slower from 2000 to 2015.The average vegetation NPP was 244.2 g C·m^-2,and the average growth rate of vegetation NPP was 3.62 g C·m^-2·a^-1.The spatial distribution of vegetation NPP was higher in the southeast and lower in the northwest.The growth of vegetation NPP areas are mainly distributed in the central and southwest,about89.8%of the total area of the loess plateau.The area where vegetation NPP decreased accounted for about 10.2%of the total area,and they mainly distributed in the southeast and northwest of the study area.The proportion of vegetation types was statistics as follows,grassland 42.1%,cultivated land 30.1%,forest land 27.8%.The annual average NPP value of grassland was the smallest with 205.6 g C·m^-2.The annual average NPP value of woodland was the largest with 290.5 g C·m^-2,and the NPP growth rate of cultivated land was the fastest(4.2 g C·m^-2·a^-1).In terms of spatial distribution,low-quality(NPP value between 0-200 g C·m^-2)grassland and cultivated land were distributed in the northern Inner Mongolia Autonomous Region,and low-quality forest land was distributed in Shanxi Province.high-quality(NPP value greater than 300 g C·m^-2)Grassland,cultivated land and woodland were all distributed in the southern part of the Loess Plateau.The increased areas of NPP of different vegetation were larger than the decreased area.The area of grassland NPP increase was the largest,and the growth trend was the most obvious in the middle of the Loess Plateau.the NPP of arable land showed a decreasing trend in the northern part of the Loess Plateau,and it showed an increasing trend in other areas of the Loess Plateau.the area of woodland NPP decreases the most with 28%,which were distributed in Shanxi Fenhe River Basin.(3)The climatic driving factors of vegetation NPP in the Loess Plateau and their changing laws are analyzed.The area ratio of the Loess Plateau where vegetation NPP was significantly positively correlated with climatic factors were listed as follows,annual cumulative precipitation 41.7%,annual effective precipitation days 37.3%,annual heavy precipitation24.0%,annual average temperature 2.2%,annual lowest Temperature 0.3%,Annual maximum temperature 0.2%.The annual maximum temperature was significantly negatively correlated with vegetation NPP and the area ratio was the highest with 64.4%,and other climate factors had no significant correlation with vegetation NPP.different driving factors accounted for the total area of the Loess Plateau.The area ratio was statistics as follows,annual maximum temperature 34.7%,annual cumulative precipitation 33.9%,annual effective precipitation10.4%,annual heavy precipitation 8.4%,annual average temperature 7.1%,annual minimum temperature 5.4%.Annual cumulative precipitation was the most important driving factor for vegetation NPP changes in the Loess Plateau,and the average relative contribution rate was the highest.Annual maximum temperature was the limiting factor for vegetation NPP in the central part of the Loess Plateau.Vegetation growth was limited by the increase of annual minimum temperature in high altitude areas of the western Loess Plateau.Climatic factors had different effects on different vegetation.Grassland NPP was driven by total precipitation increasing with the increase of precipitation.Cultivated land NPP was limited by the combined action of annual maximum temperature and precipitation.The NPP of forest land was less affected by climate fluctuation,indicating that the resistance of forest land was stronger than that of grassland and cultivated land.