Spatial And Temporal Variation Of Forest Land And FVC In Yichun Form 1991 To 2015

Forest land is the carrier of forest resources and an important part of vegetation.Obtaining forest land change information in real time,accurately and quickly and determining fractional vegetation coverage information is of great significance in assessing vegetation growth status and monitoring and management of forest resources.Yichun is China's largest forest industrial base,is known as the "the forest capital of the motherland."It is of great significance to study the changes of forestland and its FVC to understand the climate change in Northeast Asia and the ecosystem changes in Yichun City.However,there are few studies on the change of forest land in Yichun for a long time.In this paper,we take the city of Yichun as the research object,based on the image of Landsat time series in the period from 1991 to 2015,the post-category comparison method was used to detect changes in the woodlands in Yichun during 1991-2015,and the number of forest lands in Yichun was analyzed.The fractional vegetation coverageofYichun from]991 to 2015 was estimated based on dimidiate pixel model,and the changes of forest land quality in Yichun were analyzed.The main conclusions are as follows:(1)Change the selection strategy of training samples,select the stable pixels as training samples to detect the change of forest land in Yichun during 1991 to 2015,and the accuracy of the results is compared with those obtained by traditional visual interpretation.The experimental results show that:the overall accuracy of the test results obtained by stable pixels was increased by 4%to 90.09%.In addition,the stable pixels as training samples improved the classification accuracy of shadow,mist and arable land.(2)Estimation of fractional vegetation coveragein Yichun by dimidiate pixel model.NDVIv and NDVIs were interpolated based on the NDVI of pure soil samples and pure vegetation samples by Ordinary Kriging method.The results of interpolationwere used as parameters of input model,and the FVC of Yichun from 1991 to 2015 was estimated year by year.Compared with the statistical threshold method,the experimental results showed thatthe RMSE is reduced by 0.017(a relative decrease of 10.4%).(3)From 1991 to 201 5,the forest land area and FVC in Yichun showed a trend of decreasing first and then increasing.The quantity and quality of forest land increased.In 2015,the forest land area and FVC in Yichun reached 29,899.89 square kilometers and 0.96 respectively.The spatial distribution of forest land and FVC in Yichun is closer to urban,the lowerforest area and FVC,the greater the coefficient of variation.During the 1991-2015,the proportion of basically unchangedFVC areas in Yichun was the largest,accounting for 50.92%;the proportion of improved areas was much higher than the proportion of degraded areas.The change of forest land area and FVC in Yichun is affected by the annual average temperature and precipitation,both the FVC and the forest land area in the study area have been positively correlated with the annual average temperature and precipitation,and have a higher correlation with annual precipitation.In addition to natural factors such as precipitation and temperature,human activities and national macro policies play an increasingly important role in the impact of forest land.