Study On Vegetation Cover Change Of Maolan In Guizhou Based On Time-varying Consistency Of NDVI

Vegetation is the significant part of the terrestrial ecosystem and the main driving force for the ecological change of the earth.Furthermore,it has a profound impact on the basic national policy of environmental protection in China,consequently,it has important research significance.Besides,with the rapid development of surface observation technology,remote sensing has become a key means to study vegetation cover change.However,at present,due to being limited by the factors such as the image spatio-temporal resolution and the influence of cloud coverage on image quality etc.,most of the researches on the long-term sequence of vegetation cover change mainly focus on single-factor analysis at the large regional scale.And the relevant researches on the analysis at the small and medium regional scale is not deep enough.Therefore,based on the Landsat TM / ETM+/ OLI data,this thesis takes the Guizhou Maolan National Nature Reserve,which has important research value and distinctive regional characteristics,as the research area.With the comprehensive application of modern remote sensing technology,GIS technology and mathematical statistics analysis method,and with the cross application of multiple disciplines,the change of forest vegetation in Maolan karst forest in the past 18 years was studied.And by selecting the Normalized Difference Vegetation which has been widely used to characterize the surface vegetation coverage Index,NDVI as an indicator to reflect vegetation cover change,the thesis aims to propose and utilize a processing method of NDVI time-varying consistency of NDVI to eliminate the impact of cloud cover,so as to establish a more complete NDVI time sequence in the research area.On this basis,the spatio-temporal characteristics of the research area's vegetation cover change and their causes were analyzed in the thesis.And the net primary productivity(NPP)of vegetation was also computed to further calculate the amount and value of carbon-fixed oxygen released in the area.The analysis and calculation provide a scientific foundation for enhancing the adaptability of ecological civilization in Maolan reserve construction to climate change,and also supply the technical support for vegetation coverage studies at a small regional scale.Based on these researches,some basic conclusions are drawn as follows.(1)The principle of the processing method based on the time-varying consistency of NDVI is Abstract simple,clear and convenient to operate.And after the qualitative and quantitative evaluation of the results,it is found that the NDVI image of the research area after processing does has a good visual effect,and the cloud coverage area can display the distribution rule of vegetation coverage.In addition,the overall root mean square errors of all processing results and different categories are less than 0.05,thus,the impact of cloud coverage is able to be solved effectively and the vegetation coverage time sequence of the research area can be constructed.(2)From the perspective of time transformation's features,the vegetation coverage in the research area is well at present,and the holistic situation is significantly better than that in 1999.What's more,the vegetation coverage in the residential and surrounding areas has also been remarkably improved.In the past 18 years,the average NDVI fluctuated from 0.6975 to 0.8001 from September to October every year,presenting a prominent trend of slowly increasing.At the aspect of spatial distribution's characteristics,the NDVI distribution of Maolan Nature Reserve presents a typical structure of “peanut shell”.And the overall vegetation coverage shows an upward trend with positive growth area and negative growth area accounting for 90.20% and9.80% respectively.The overall vegetation coverage in the study area is increasing and the rate in the eastern region is higher than that in the western region,with low coefficient of variation and stable holistic change.Moreover,the vegetation cover changes' isotropy is slightly stronger than the reverse,however,the area that may be degraded will be more than the improved area in the future.Besides,there exist conspicuous discrepancies in the spatial distribution characteristics of vegetation coverage in the residential and forest areas.(3)Among the four types of influence factors,the geological background has a long-term negative limit and influence on the vegetation coverage in the research area.In addition to the impact of topography on vegetation growth in the area from the aspects of sunlight absorption,soil and water conservation,as well as temperature and humidity,it also has a joint effect with human activities.Furthermore,there is a significant positive correlation between meteorological factors and vegetation cover change in the area,in which the impact of average temperature is the strongest in the current month,while the influence of precipitation and average relative humidity exists hysteresis on the contrary.There are obvious differences in vegetation cover characteristics between residential areas and forest areas,and human activities'affecting vegetation coverage in the area is simple and direct.In detail,the closer the area is to the center of human activities,the Abstract lower the vegetation coverage it has,the higher the NDVI growth rate becomes,the larger the coefficient of variation increases,and the stronger the anti sustainability will be.In other words,it indeed reflects the decisive position of human beings in the modern environmental protection strategy.(4)Above all,the Maolan Nature Reserve owns a fairly strong capacity for carbon fixation and oxygen release.By 2016,the total carbon fixation per unit area of the entire study area in September was about 0.57 t / hm2,and the oxygen release per unit area was about 1.52 t / hm2.And they can produce about 11,430 t of carbon fixation and about 30,600 t of oxygen release.The total value of carbon fixation and oxygen release is up to around 44.32 million yuan.Besides,it shall be noted that the vegetation cover change in the research area has a positive correlation with carbon sequestration and oxygen release,but this sort of impact is not only limited by it.