Vegetation Dynamics, Patterns and Carbon Sinks in Chongqing Based on RS, GIS, DEM and NDVI
|Keywords||Vegetation remote sensing NDVI object-oriented image classification method Chongqing Jinyun Mountain carbon density|
Global warming, one environmental problem recognized by the international community, has resulted in climate fluctuation which would produce a far-reaching impact on human survival, economic and social development. Since plants could absorb and store CO2, one of the main greenhouse gases caused global warming, and the plantation was regarded as a huge carbon sink, the plants play an important and irreplaceable role in global change mitigation. The change of vegetation areas, plantation composition and quality condition, distribution pattern, and potential for carbon sequestration, will impact the regional environment and global change. Therefore, it is essential for theoretical and practical research on dynamics, distribution pattern, and carbon sink capacity of vegetation. Chongqing located in the key zone of the Three Gorges reservoir area, and is the major water resources strategic reserve library in China and an integral part of the important carbon reservoir area in southwest China. The national nature reserve region of Jinyun Mountain is a typical area with rich-resource vegetation in Chongqing and sub-tropical region. In addition, since Chongqing has become direct controlled municipality, the establishments of Three Gorges Reservoir and Chongqing economic development and "foresting Chongqing" construction have made remarkable achievements. Hence, concerning about Chongqing and Jinyun Mountain vegetation, their dynamics and patterns of carbon stocks would have strategic significance to vegetation and carbon sequestration business and management aiming to increase sequestration and slow down global warming, and would provide useful theory and data for the planning and development of Chongqing.Vegetation dynamics of Chongqing and its metropolitan region based on RS,GIS and NDVI Vegetation characteristics of the horizontal pattern and dynamic about nearly30years in Chongqing and its metropolitan region were analyzed through the NDVI of Pathfinder AVHRR and SPOTVGA, The NDVIs were extracted from Landsat satellite remote sensing image at1978a,1988a,2000a and2007a to analyzed vegetation change in the metropolitan region of Chongqing City. The results showed that the Chongqing vegetation had a significant interannual variation. From December to next February, the vegetation growth and metabolism were inactive, and its activity was presented from May to October in each year. Chongqing vegetation was well-grown in the past10years as a whole. Areas of vegetation growing in an obviously good condition were concentrated in the center-north of Chongqing, such as Fangdou mountain, Jinghua mountain and Jiajiao mountain, and mountain regions of southeastern Chongqing. The negative vegetation growing region appeared in the metropolitan region of Chongqing City, Changshou and Wanzhou District, etc., which were the city center area. Vegetation did not degrade in Wuxi, Chengkou and the Qijiang county. Additionally, the largest area of vegetation deterioration appeared in the metropolitan region of Chongqing City, reached nearly420km, followed by the Changshou and Fengjie county. Study about vegetation dynamics of Chongqing metropolis in nearly30years showed that the vegetation growing area were appeared in northeast and south regions, such as Jinyun mountain, Huaying mountain, Tongluo mountain in the north, and Zidang mountain, Shengden mountain in the south of Chongqing metropolis. On the contrary, the vegetation in west of metropolitan region was more degraded or disappeared. In conclusion, vegetation of Chongqing was in a good condition and compensated for the adverse effects of degradation or disappearance vegetation in the process of urbanization. Protecting the well-developed vegetation in mountain area, as well as controlling the negative impact of urban development on the vegetation, is the key measures to maintaining and improving Chongqing vegetation quality.The vegetation classification using high resolution remote sensing, digital elevation model, geographical information system and object-oriented image classification in Chongqing——a case study on Jinyun MountainIn the vegetation classification study, object oriented multi-level classification was used in interpreting Jinyun vegetation from the high-resolution remote sensing image and1:10000relief maps were used to generate digital elevation model respectively. Then vegetation of study area were exacted from the WorldView-2remote sensing image acquired in September2010. The vegetation types were divided into broad-leaved evergreen, mixed coniferous and broadleaved evergreen, coniferous forest, mixed coniferous and neosinocalsms stand, moso bamboo stand, neosinocalams stand and shrubbery. The preliminary classification results were interpreted, topology pocessed and statistical analyzed in ArcGlS. The results of classification of Jinyun vegetation showed a high recognition and classification accuracy based on object-oriented image multi-level classification approach with manual interpretation. Its overall accuracy was higher than89.22%and the classification results of vegetation had the obvious borders and homogeneous internal homogeneity. The results showed that the study area was3468.41hm2. Coniferous forest and shrubbery stands were dominated vegetation and their areas were reached1048.56hm2and729.64hm2respectively, the ratio of their areas accounted for51%of the study area, followed by mixed coniferous and broad forest, which area is537.26hm2. Water bodies, roads and other artificial surface were accounted for7%, and the total areas are242.32hm2. Therefore, high-resolution remote sensing images, high-resolution topographic maps, are efficient tools for researching large-scale forest vegetation spatial characteristics. Combined with the DEM and based on object-oriented classification and interpretation methods, and using the thematic maps of vegetation, can provide basic technology and useful data to support the researching of spatial distribution vegetation and carbon storage in Jinyun Mountain.Spatial distribution of vegetation and carbon density in Chongqing based on RS/GIS——a case study on Jinyun MountainIn this study, high-resolution remote sensing image and1:10000relief maps were used to generate Jinyun vegetation map and digital elevation model respectively, combining with a non-destructive method to acquire forest biomass by field investigation and the data of carbon content and biomass regression models from the published papers. And then, the spatial characteristics of vegetation and carbon density in Jinyun Mountain Natural Reserve were analyzed by ArcGIS. The results showed that CF was the dominating forest stand, followed by SH (shrub). The vegetation area ranged as CF (coniferous forest,30%)> SH (21%)> MCB (evergreen broad-leaved forest,16%)> NS (neosinocalams stand,11%)> EBF (evergreen broad-leaved, forest6%)> MCN (mixed coniferous and neosinocalsms stand,5%)> MBS (moso bamboo stand,4%). The average vegetation carbon density in Jinyun Mountain was50.45MgC/hm2, which was higher than the average level in China, ranged as MCB (74.23MgC/hm2)> CF (62.97MgC/hm2)> EBF (62.65MgC/hm2)> MCN (59.84MgC/hm2)> NS (48.72MgC/hm2)> MBS (47.88MgC/hm2)> SH (10.66MgC/hm2). Moreover, vegetation and carbon density had clear spatial variations with altitude, slope and aspect. CF dominated in altitude higher than500m and slope>15°, but the shrub was the other way around. The carbon density of MCB and EBF increased with the increasing of altitude and slope. EBF had a large area in the northwest aspect, and MCB had a large distribution in the north, northwest, east and southeast aspects. NS and MCN were the dominating forest stand in the south relatively. CF, dominated with Pinus massoniana, and SH were at the primary stage of forest recovery succession in the Jinyun Mountain. The results indicate that the actual carbon sequestration of Jinyun Mountain is still much lower than the potential value of the zonal climax vegetation in this subtropical area. As we find the carbon storage and density are negatively correlated with human disturbance, forest reserve managements, such as enclosure of forest region, might contribute to conserve and sequester carbon in Jinyun Mountain.The vegetation carbon density of different successional stages in Jinyun MountainIn this study, the different forest ecosystems carbon densities were researched through calculating vegetation, litter and soil carbon density. And the carbon density and its distribution pattern characteristic of different successional series of vegetation ecosystems were also discussed. It was researched that potential carbon stock and its characteristic in succession process as well. The results showed that,(1) carbon density in the four successional vegetation ecosystems were consistent with its sequence of successional stages, ranged by broadleaved evergreen(347.96MgC/hm2)> needle-broadleaved evergreen(140.19MgC/hm2)> coniferous forest(107.92MgC/hm2)> shrubbery(51.28MgC/hm2).(2) As the main ecosystem constituents of ecosystem carbon sinks, vegetation and litter carbon density in the succession sequence showed an increasing tendency with the successional times. The mean value of vegetation and litter carbon density increased from10.57MgC/hm2and4.55MgC/hm2of shrub to95.55MgC/hm2and191.33MgC/hm2of the broadleaved evergreen respectively. And soil carbon density of needle-broadleaved evergreen, coniferous forest and shrubbery were closed, ranged as33.31MgC/hm2,32.48MgC/hm2and36.45MgC/hm2respectively, and were much lower than that of broadleaved evergreen(61.03MgC/hm2).(3) Ecosystem carbon density pattern of vegetation were very different. The proportion of the vegetation carbon storage above the ground gradually increased with succession sequence, except for the zonal top forest and broadleaved forest evergreen. The proportion of soil carbon storage density showed a downward trend with the succession sequence. The proportion of shrub soil carbon density, closed to2/3of the ecosystem, was the highest. And that of the coniferous forest was about1/3of its ecosystem and that of the needle-broadleaved evergreen was closed1/4, and then that of the broadleaf evergreen was about1/5. On the contrary, the litter carbon storage proportion was increased obviously with the successional sequence, and the ratio increased from less than1/10of the shrubbery to1/2of the broad-leaved evergreen. Therefore, the broadleaved evergreen in Jinyun Mountain maintained the largest carbon reserves, and litter carbon storage played an important role in the carbon pools in this region. The vegetation in Jinyun Mountain would have a great potential increasing carbon storage in the future development and succession process, and its increasing carbon sink will mainly lead to increasing of vegetation and litter carbon pool of the ecosystem. The result also showed that the litter transformed from vegetation should be protected and managed effectively.The spatial distribution of Chongqing vegetation and carbon density based on GIS/DEM/RSIn the study, Chongqing vegetation and carbon density spatial pattern were analyzed by using1km×1km Chongqing vegetation map, combined with the data of different vegetation carbon density from the published papers and DEM, and with the ArcGIS spatial analysis module. The results showed that vegetation in Chongqing were obviously spatial distributing, with the main forest vegetation type of broadleaved evergreen and needle-leaved evergreen. These two types accounted for37.04%of the total area of Chongqing. Their areas were31899.38km2and mainly distributed in the north and south region of Chongqing, and some strip-mountains of the west and center Chongqing. West, center and north-center regions, segmented by the strip-mountains, were major agricultural areas. The total planted area reached to45629.41km2, accounting for52%of the total Chongqing area. The shrubbery area was also very large-about5732.49km2. The spatial distribution of carbon density was similar to Chongqing vegetation. High carbon density areas were concentrated in the higher elevation of north and south region. The average carbon density values of counties were from4.39MgC/hm2to54.76MgC/hm2. Chengkou and Wuxi had the highest carbon density and its mean values were54.76MgC/hm2and42.31MgC/hm2respectively. Tongnan, one county of Chongqing west, had only4.39MgC/hm2, and Chongqing average carbon density value was21.40MgC/hm2. Moreover. Chongqing carbon density had a vertical differentiation characteristic. The values of carbon density increased with increasing altitude remarkably and reached peak(53.29MgC/hm2) at2000～2200m and then decreased slightly. At an altitude of above2600m, the value was41.37MgC/hm2. The results showed that the broadleaved evergreen, needle-leaved evergreen and crops, dominated vegetation in Chongqing, made an important contribution to carbon storage. Increasing crop production and rational utilization of crop straw, as well as updating and transforming the shrubbery to the forest would be advantageous to the improvement carbon sink in Chongqing. Effectively protecting and managing forest in north and south of Chongqing, and afforesting in the west and center region timely should be the effective measures for the increasing Chongqing carbon sink. In summary, this paper aimed to study the vegetation dynamics, pattern and spatial distribution of its carbon density in Chongqing, metropolitan area of Chongqing City and national nature reserve of Jinyun Mountain, using RS, NDVI, DEM, GIS, and the data from field surveying and published papers, as well as interpreting and classifying the vegetation from the high-resolution remote sensing images. The results showed that:in the past30years, Chongqing vegetation has been in good growing and developing condition, and has been made up for the negative impact of the vegetation decreasing in the urban central area in the process of urbanization. The broadleaved evergreen and needle-broadleaved evergreen were the dominated vegetation in Chongqing and had a higher carbon density. Shrubs and herbaceous held the relatively low carbon density accounted for an important proportion. The crop cultivation area in Chongqing was mainly distributed in the low altitude area of the east and west of Chong, and occupied a large area. High carbon density areas were appeared on higher elevations where was disturbed lightly, such as the vast mountain in the north and south of Chongqing, and the strip-mountains in the center-north, center and west of Chongqing. Carbon density was increased with the increasing of elevation.Therefore, protecting and managing the forest in the north and south of Chongqing and in the mountains of the center-north, center and west of Chongqing can increase the carbon sinks effectiveness, with the measures of returning farmland to forests, replacing low carbon density plants with broadleaved evergreen and accelerating forest development rate and improving forest quality. In relatively fewer vegetation areas, such as east and west of Chongqing, afforestation, enhancing crop yield and using straw effectively would increase carbon sinks. In conclusion, carbon has been stored more by Chongqing vegetation, and it has been an important carbon pool in southwestern China. The features of Chongqing vegetation and carbon storage changing dynamics, patterns and variation tendency of carbon density present that Chongqing would still have an important carbon sink potential in the future for a long time.