| Compared with industrial emission reduction,high-tech carbon capture and carbon storage technologies,vegetation carbon sinks in terrestrial ecosystems are more efficient,economical and sustainable,and have multiple benefits.Natural conditions and man-made land use and cover changes are important reasons for vegetation biomass production and carbon source and sink changes in terrestrial ecosystems.Therefore,a correct understanding of vegetation carbon sequestration capacity and its influencing factors is conducive to better connecting the goal of"realizing the synergistic effect of carbon reduction and pollution reduction"in the period of"14th Five-Year Plan",and implementing more scientific carbon reduction and sequestration measures.Using the remote sensing data of 2005,2010,2015 and 2020,the CASA model was established by using NDVI data,climate data and vegetation static parameter data to estimate the net primary productivity(NPP)and vegetation carbon sink of each ecosystem in Kunming City.The temporal and spatial differences of land use type change and vegetation carbon sink were analyzed.Arcgis technology and correlation analysis were used to identify the effects of terrain factors and climate factors on vegetation carbon sink,and CA-Markov model and Stacking integrated learning method were used to simulate and predict future land use and vegetation carbon sink in Kunming City.The following conclusions are drawn from the research:(1)From 2005 to 2020,a total of 2,736.27 km~2of land use type conversion occurred in Kunming City,with the overall area of cultivated land,woodland and grassland continuously decreased,while the area of construction land increased significantly.By the end of 2020,the area of cultivated land,forest land and grassland has decreased by 255.8km~2,133.52km~2and 328.63km~2respectively,while the area of water area,construction land and unused land has increased by 39.89km~2,675.29km~2and 2.78km~2respectively.(2)From 2005 to 2020,the mean NPP and carbon sink of vegetation in the terrestrial ecosystem of Kunming showed an overall upward trend,while the area of low-value NPP showed an overall downward trend,while the area of median and high-value NPP showed an overall upward trend.By the end of 2020,the mean NPP and carbon sink of vegetation were 637.98g C/m~2and 377.47×10~4t,respectively,which increased by 120g C/m~2and 71.42×10~4t compared with 2005.(3)By the end of 2020,the vegetation carbon sinks of cultivated land,forest land,grassland,water area,construction land and unused land were 59.81×10~4t,202.67×10~4t,96.33×10~4t,3.61×10~4t,14.6×10~4t and 0.89×10~4t,respectively.From2005 to 2020,the land use type conversion in Kunming resulted in 31088.09t of vegetation carbon sink loss and 4271.63t of vegetation carbon sink gain,resulting in26816.46t of vegetation net carbon sink loss,among which the occupation of cultivated land,woodland and grassland for construction land was the main cause of vegetation carbon sink loss.They accounted for 29.42%,22.56%and 20.62%of vegetation carbon sink loss,respectively,accounting for 72.59%.The conversion of wasteland into woodland and arable land,and the conversion of construction land into water area,can bring vegetation carbon sink benefits.(4)Topographic factors significantly affect the mean NPP and carbon sink of vegetation:in terms of elevation,the mean NPP of vegetation increases with increasing altitude below 2500m,while the mean NPP of vegetation decreases with increasing altitude above 2500m.Vegetation carbon sink is mainly distributed in areas between 1500m and 2500m.In terms of slope aspect,the average NPP of vegetation presents northwest>North>Northeast>West>East>Southeast>Southwest>South>Flat land;The overall carbon sink of vegetation is northwest>West>Southeast>East>Northeast>Southwest>North>South>Flat land.In terms of slope,the average NPP of vegetation is 26-35°>16 to 25°>36 to 45°>6 to15°>45-90°>0-5°,vegetation carbon sink is ranked as 6-15°>16 to 25°>26-35°>0-5°>36 to 45°>45-90°.In terms of soil factors,the average NPP of vegetation was yellow soil>Swamp soil>Brown soil>Yellow brown soil>Red soil>Purple soil>Coarse bone soil>Lime(rock)soil>Dark brown soil>Mountain meadow soil>Meadow soil>Paddy soil>Dry red soil>New accumulated soil>Urban area>Black felt soil>Lakes and reservoirs;The order of vegetation carbon sink is red soil>Brown soi>Yellow brown soil>Paddy soil>Yellow soil>Dry red soil>Dark brown soil>Purple soil>Lakes and Reservoirs>Black felt soil>Mountain meadow soil>Swamp soil>Lime(rock)soil>Urban area>New accumulated soil>Meadow soil>In coarse bone soil,vegetation carbon sink in red soil area accounted for 62.8%of the total vegetation carbon sink in the city.The relationship between social and economic factors and vegetation carbon sink is as follows:There is a positive correlation between vegetation carbon sink and the number of primary industry and population,and a negative correlation between vegetation carbon sink and per capita local fiscal revenue.(5)The predicted areas of cultivated land,forest land,grassland,water area,construction land and unused land in Kunming in 2025 are 3858.66km~2,9352.63km~2,5621.79km~2,507.69km~2,1562.53km~2,and 72.01km~2,respectively.Compared with2020,the reduction rate of cultivated land and forestland area and the increase rate of construction land area have slowed down.In 2025,the predicted vegetation carbon sink of Kunming was 392.2055×10~4t,which increased by 14.74×10~4t compared with2020.Except for Jinning District,vegetation carbon sink showed a decreasing trend,other districts/counties showed an increasing trend.Among all land use types,vegetation carbon sink showed an increasing trend except for primary grassland.According to the calculation results,this paper puts forward the following countermeasures and suggestions:(1)strengthen the protection of woodland and grassland to ensure the quantity of cultivated land;(2)Suitable planning of land use type and optimizing land use structure;(3)Scientific management and protection of ecological vegetation to improve the carbon sequestration capacity of vegetation. |
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