Estimation Of Net Primary Productivity Of Vegetation In Heilongjiang River Basin And Study On Influencing Factors

The Heilongjiang River Basin has a vast area,complex and diverse vegetation types and rich biodiversity.The vegetation and its ecological functions in the study area are very sensitive to global climate change.The net primary productivity(NPP)of vegetation is an important indicator to measure the growth status of vegetation on the surface.It reflects the distribution of vegetation and plays an important role in evaluating the structure and function of regional ecosystems.The role of vegetation in ecosystem carbon cycle and maintaining system carbon balance is becoming more and more important.Based on the CASA model,this paper uses the MODIS13A3-NDVI data,vegetation cover type data,precipitation,temperature and solar radiation data from2001 to 2020 to simulate the net primary productivity of vegetation in the Heilongjiang River Basin,and explore the time and space of vegetation NPP in the Heilongjiang River Basin under long-term time series.Distribution pattern and dynamic change characteristics,and using correlation analysis method,combined with temperature,precipitation and vegetation coverage data,to explore the driving factors of vegetation NPP changes,which are important for the improvement of vegetation productivity,environmental protection and future development planning in the Heilongjiang River Basin.It has important reference significance.The following three conclusions were drawn from the research:1.The temporal and spatial variation characteristics and stability of vegetation NPP in Heilongjiang River Basin(1)From the perspective of the time change of NPP,The annual mean value of vegetation NPP in the Heilongjiang River Basin showed an overall upward trend over time.and the fluctuation was relatively stable.(2)From the perspective of the spatial distribution and changing trend of NPP,the overall spatial distribution pattern of vegetation NPP in the Heilongjiang River Basin in the past 20 years is " The north and south are lower,the east is higher and the west is lower”.The average annual vegetation net primary productivity in the Heilongjiang River Basin was 302.34 g C·m-2·a-1,and the average annual vegetation NPP range in the Heilongjiang River Basin from 2001 to 2020 was 0-615.29 g C·m-2·a-1.The proportion of the research area showing an upward trend and a downward trend were 65.97% and34.03%,respectively.(3)From the point of view of the stability of the spatial variation of NPP,the coverage areas of regions with stable and very stable changes accounted for 67.62% and0.58%,respectively.2.Spatial and temporal variation characteristics of different impact factors(1)The overall change trend of the temperature in the Heilongjiang River Basin from 2001 to 2020 showed a trend of insignificant fluctuation and increase.The average temperature for many years is-0.62?,and the annual average temperature change is-3.07-1.61?.The area with an increasing trend of temperature is mainly located in the southeast,accounting for 30.79%,while 69.21% of the area has a decreasing trend.It was more pronounced in the northern part of the study area.(2)From 2001 to 2020,the overall precipitation in the Heilongjiang River Basin showed a slow increase trend,and the average annual precipitation for many years was599.07 mm.Most areas in the northwest and east showed a decreasing trend,accounting for 51.32%,Most of the areas showing an increasing trend are in the middle of the study area,accounting for 48.68%.(3)From the perspective of the time change of FVC,FVC showed a significant growth trend,and the inter-annual variation fluctuation was generally small,and it basically remained in a relatively stable state.From the perspective of the spatial distribution and changing trend of FVC,the vegetation coverage level in the eastern part of the Heilongjiang River Basin is generally higher than that in the western region;the area proportion of the area where FVC has increased in the past 20 years is 84.7%,while 15.3% of the area has decreased FVC From the perspective of the stability of the spatial variation of FVC,the very stable area covers the largest area,accounting for66.59%,and the area that is stable is 29.38%.3.Correlation between different factors and vegetation NPP(1)The results show that the areas where the average annual temperature and annual precipitation have a positive impact on the growth of NPP in the Heilongjiang River Basin are 61.91% and 36.65% of the study area,respectively.(2)The results showed that the areas where the average annual temperature and annual precipitation had a positive impact on the growth of FVC in the Heilongjiang River Basin were 83.52% and 44.35% of the study area,respectively.(3)The results show that the average correlation coefficient between NPP and FVC is 0.38,and there is a spatial distribution difference of “positive in the south,negative in the north,negative in the east,and negative in the west”.There are 88.17% of the regional vegetation NPP in the Heilongjiang River Basin.There was a positive correlation between FVC and FVC,and the correlation between FVC and vegetation NPP was strongest in medium and high coverage areas.The results show that the main cause of climate change affecting NPP and FVC vegetation changes in the Heilongjiang River Basin is the average annual temperature.The temporal and spatial changes of FVC and NPP and their responses to meteorological factors have a certain consistency,which further proves that the average annual temperature is the main meteorological factor affecting vegetation NPP in the Heilongjiang River Basin.