The Spatial And Temporal Dynamic Change Detection Of Vegetation And The Quantification Of Driving Factors In Northeast China

As an essential part of the terrestrial ecosystem,vegetation plays a crucial role in promoting ecological balance,improving regional climate change,conserving water sources,and conserving water and soil.However,under the background of global climate change and the impact of human activities,vegetation status on the ground has undergone very complex changes in the past few decades.Excavating the characteristics of temporal and spatial changes of vegetation and exploring the driving factors of the changes can help deepen the understanding of vegetation change and provide a scientific basis for the rational development of natural resources,land space utilization,and ecological environment protection.Northeast China has formed a unique vegetation distribution pattern due to its diverse climate and complex terrain.Also,it has experienced relatively violent human activities,including land reclamation and afforestation,in the past few decades.So Northeast China is a hot area to research vegetation dynamic change detection and driving factors.Given those above,based on the GIMMS NDVI3 g,climate factor,and land use data from 1982 to 2015,this research used thin-plate splines interpolation,trend analysis,mutation detection,correlation analysis,regression analysis,and residual analysis,etc.to analyze the spatial-temporal variation characteristics of climate factors,land use,and vegetation.This paper constructed a quantitative method framework of vegetation change driving factors.The driving factors were distinguished and quantified of vegetation change trend and mutation.The main conclusions obtained are as follows:(1)The annual average temperature of Northeast China increased significantly from 1982 to 2015,with a tendency of 0.254 ?/10 a(P<0.05).The areas where temperature increased rapidly were the southern Da Hinggan Mountains,Xiao Hinggan Mountains,and eastern Songnen plain.The temperature rise rate of 1982-2008 is about twice that of the whole period,and the temperature has a turning point from high temperature to low temperature in 2008-2009.Precipitation in Northeast China fluctuated wildly and showed a slight decreasing trend from 1982 to 2015.The decreasing rate was-4.979 mm/10a(P>0.05),and the annual precipitation in most areas of the region showed a downward trend.The annual precipitation series had a turning point from high to low during 1998-1999 and established a significant upward trend after 1999.Forest,farmland,and grassland were the main land types in the Northeast,accounting for nearly 90%.Between 1980 and 2015,the increase of farmland was the largest,mainly due to the conversion from grassland,forest,and unused land.(2)The order of NDVI value of different land-use types was rough as follows:woodland> cultivated land,marshland>grassland>saline-alkali land>sandy land.The NDVI of cultivated land differs significantly in the early and late growing seasons.The NDVI peak of forest land mostly appeared in July while that of grassland and cultivated land appeared in August The order of seasonal NDVI value was summer>growing season>autumn>spring.The spring NDVI in the Sanjiang Plain and the eastern Songnen Plain decreases significantly,while the autumn NDVI shows the opposite trend.The spatial distribution of the NDVI trend in summer is consistent with that in the growing season.The spatial distribution of annual maximum NDVI and annual average NDVI was different,and the order of difference was farmland > woodland >grassland.Compared with the annual maximum NDVI,the annual average NDVI identifies more areas with a significant decrease.This trend difference in the distribution area of cultivated land was mainly different.From 1982 to 2015,52.87%region of Northeast China had a break point in trend,which had regional differentiation characteristics in spatial distribution.The mutation amplitude of NDVI mainly changed from high value to low value,that is,negative mutation.Among them,the front and back trend types with large mutation ranges were "decrease/increase" and "increase/increase".The former was mainly distributed in the southern Da Hinggan Mountains,while the latter was distributed primarily on the northern Da Hinggan Mountains,Xiao Hinggan Mountains,and Changbai Mountains.(3)Human activities were the dominant factor in the change of vegetation trends in Northeast China from 1982 to 2015.The contribution rates of climate change and human activities in the significant improvement of vegetation were 24.97% and75.03%,respectively.Human activities dominated the vegetation improvement of Songnen Plain,western Liaohe Plain,Xiao Hinggan Mountains and Sanjiang Plain.The improvement of vegetation in the northern Da Hinggan Mountains was mainly dominated by temperature.The improvement of vegetation in the Hulunbuir Plateau was related to precipitation and human activities.The improvement of vegetation in southern Changbai Mountain was related to temperature and human activities.The contribution rates of climate change and human activities in the significant degradation of vegetation were 36.60% and 63.40%.The vegetation degradation in the southern Da Hinggan Mountains was mainly dominated by precipitation.The vegetation degradation in the northern Songnen Plain was related to temperature and human activities.Human activities dominated the vegetation degradation in the eastern Liaohe Plain,the southern Changbai Mountain,and parts of the Sanjiang Plain.Expansion of cultivated land was the primary form of human activity that causes vegetation degradation,invading woodland,grassland,and swamp.Climate change was the dominant factor of vegetation mutation in Northeast China from 1982 to 2015,and79.66% of vegetation mutation was affected by climate change.The negative mutation of vegetation in the southern Da Hinggan Mountains,the western Liaohe plain,and the southern Changbai Mountain was caused by the decrease of precipitation.The decrease in temperature caused the negative mutation of vegetation in the northern Da Hinggan Mountains.The negative mutation of vegetation in the western and northern of Songnen Plain was caused by decreased precipitation and the increase of temperature.20.33% of vegetation mutations were affected by human activities,distributed in the central of Da Hinggan Mountains,central of Songnen Plain,Xiao Hinggan Mountains,Sanjiang Plain,and northern Changbai Mountain,mainly negative mutations.