| Net primary productivity of vegetation is an important part of the ecosystem's carbon cycle and the main factor that regulates the ecological process.It directly reflects the production capacity of vegetation under natural environmental conditions and the quality of terrestrial ecosystems,and plays an important role in global climate change and carbon balance.Therefore,it has important theoretical and practical significance to study the characteristics of the spatial and temporal changes of the vegetation net primary productivity and to explore its response to environmental factors and future development trends in the Weihe Waterashed.Based on remote sensing image data,meteorological observation data,digital elevation model data and land use type data,and using Arc GIS10.2,ENVI5.3,IDRISI SELVA and other software as technical means,the net primary productivity of vegetation in the Weihe Watershed in 2000,2006,2012 and 2018 were simulated,and its spatial and temporal characteristics were analyzed by CASA model and mean value method.Then the response of net primary productivity to various environmental factors in the Weihe Watershed were analyzed by correlation analysis.Finally,the CA?Markov model was used as research method to predict the spatial distribution pattern of net primary productivity in the Weihe Watershed in 2024 and 2030.The main conclusions are as follows:(1)On the time scale,the variation trend of net primary productivity of vegetation in the Weihe Watershed has obvious rules.The monthly change gradually increased from January to July,reaching the maximum value of 115.29g C/m~2a,and gradually decreased from July to December,reaching the minimum value of10.75g C/m~2a in January of the following year.Changes during the year have distinct seasonal and cyclical characteristics.Net primary production showed an increasing trend in spring,increasing to the maximum value of 382.08g C/m~2a in summer,and decreasing trend in autumn,dropping to the minimum value of 42.97g C/m~2a in winter.The inter-annual net primary productivity of vegetation in the Weihe Watershed is increasing year by year,indicating that the vegetation is developing well and the condition of the terrestrial ecosystem continues to improve.In terms of sub-basins,the monthly,seasonal,and annual average net primary productivity of vegetation in the Baojixia to Xianyang Watershed are the largest,which are 74.83g C/m~2a,203.65g C/m~2a,and 901.06g C/m~2a,respectively.The monthly,seasonal,and annual averages of the Jinghe Watershed are the smallest,which are 51.40g C/m~2a,147.76g C/m~2a,and 616.63g C/m~2a,respectively.(2)On the space scale,the distribution pattern of net primary productivity of vegetation in the Weihe Watershed has significant characteristics.On the whole,the net primary productivity of vegetation in the east and south of the Weihe Watershed is higher than that in the west and north.In terms of sub-basins,the net primary productivity of vegetation in the mainstream of the Weihe River is the largest,followed by the Beiluohe Watershed,and the Jinghe Watershed is the smallest,and within each sub-basin,the net primary productivity of vegetation in the upstream is higher than that in the downstream.(3)Based on the evaluation results of ecological environment factors,combined with the principle of ecological function zoning,the Weihe Watershed is divided into8 ecological function areas,which are named drought prevention and resistance areas,plain planting areas,plateau agricultural areas,animal husbandry development areas,water conservation areas,wind-proof and sand-fixing areas,vegetation protection areas,water and soil conservation areas according to the ecological environment characteristics of each area.Among them,the net primary productivity of vegetation is the largest in water conservation areas,and the net primary productivity of vegetation is the smallest in drought prevention and resistance areas.It shows that a good ecological environment and the growth and development of vegetation have a certain mutual promotion.Areas with a good ecological environment tend to have higher net primary productivity of vegetation and stronger carbon sequestration capacity of vegetation,thereby promoting a virtuous cycle of free carbon and maintaining ecology.The carbon balance of the system will ultimately have a positive impact on the ecological environment.(4)The temperature,precipitation and radiation in the Weihe Watershed have significant temporal and spatial distribution characteristics.On the time scale,the changes during the year of the three have obvious seasonal characteristics.In spring and summer,the temperature is high,the precipitation is large,the solar radiation is strong,and in autumn and winter,the temperature is low,the precipitation is small,and the solar radiation is weak.The annual difference in temperature is 27.54?,the annual difference in precipitation is 109.06mm,and the annual variation in radiation is 3.85MJ/m~2.The inter-annual variability is manifested by the overall climate showing a warm and humid trend year by year,while the amount of radiation remains basically stable.On the space scale,the eastern and southern regions have higher temperature and greater precipitation than the western and northern regions,and the differences in temperature and precipitation between the sub-basins are small.Affected by altitude,the amount of radiation in the north of the Weihe Watershed is significantly higher than that in the south.(5)There are certain differences in the response of the net primary productivity to environmental factors in the Weihe Watershed.In terms of time,the response to temperature and precipitation is mainly manifested as a significant positive correlation,and the response to temperature is stronger than precipitation,indicating that temperature changes are more likely to affect the growth and development of vegetation.The spatial response to temperature and precipitation is mainly a slight positive correlation.The response to temperature is stronger in the south than in the north,and the response to precipitation is stronger in the west than in the east.The response to radiation is mainly manifested as a positive correlation,showing the characteristics of being stronger in the east and south than in the west and north.The response to topographical factors is shown as a bimodal curve with increasing elevation;it shows a trend of increasing with the increase of slope,but the rate of increase keeps decreasing;the difference with the aspect change is that the net primary productivity of vegetation on the north and west slopes is higher,and the net primary productivity of vegetation on the south and east slopes is lower.(6)The future development trend of the terrestrial ecosystem in the Weihe Watershed is good.The prediction results of the spatial distribution pattern of vegetation net primary productivity in the Weihe Watershed in 2024 and 2030 show that the overall development of vegetation net primary productivity is in good condition and is showing a trend of continuous improvement.The areas of low-value areas and lower-value areas of vegetation net primary productivity continue to decrease,the areas of medium-value areas and higher-value areas show a significant increase,and the areas of high-value areas basically remain stable.The low-value areas and the lower-value areas are distributed in the northern part of the Jinghe Watershed,shrinking to the west and north,the medium-value areas.The medium-value areas and higher-value areas are distributed in the western and middle areas of the watershed and the Guanzhong Plain,expanding to the north and west.The spatial distribution range of high-value areas is basically unchanged,including mountains such as Qinling,Ziwuling and Liupan Mountains. |
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