Vegetation Change Trend In Northern Latitudes Nearly 4 Decades

Pan-Arctic area belongs to the high latitudes,and the vegetation in Pan-Arctic mainly belongs to the temperature-limited ecosystem.Thus,the vegetation is sensitive to global warming.Climate warming leads to vast changes in the land cover types and plant biomass in the northern high-latitude regions.Climate conditions overall facilitate vegetation growth in the Arctic,with the truth tree line moving northern latitudes and shrubification in scientific research.There are different trends between vegetations.A vegetation atlas with high accuracy is the scientific basis for the study of the response of vegetation to climate change and its driving mechanisms.There are many challenges to Pan-Arctic vegetation types mapping,which can be attributed to several reasons such as differences in field survey data,standards for the land cover types classification,the great heterogeneities in the tundra ecosystem,and differences in mapping methods and difficulties of optimizing algorithm.To find vegetation change trends and patterns,this study includes two works in the following:(1)we analyzed different land cover areas change based global land cover dataset and CRU TS in northern 40°N and probed the pattern of vegetation changes.The results indicated that forest and shrubland areas increased as a large area of grassland shifted to forest and shrubland.The snow/ice,tundra,and grassland largely decreased from1982 to 2015.Although approximately 277.3×103 km~2 of barren land(6.2%of the total barren land area in 1982)changed to tundra,the tundra area still decreased because some tundra shifted to forest and grassland.The NDVI values of the tundra significantly increased,but the shrubland showed a decreasing trend.The temperature in the growing season(June to September)showed the largest positive correlation coefficients with the NDVI values of forest,tundra,grassland,and cropland.However,due to shrubification processes and plant mortality in shrubland areas,the shrubland NDVI showed a negative relationship with annual temperature but positively correlated with monthly t.Taken together,although there is a large room for improvement of the land cover type data accuracy,our results suggested that the land cover types in high-latitude regions changed significantly,while the NDVI values of the different land cover types showed different responses to climate change.The overall trend is of shrubland and tree lines moving northwards,while changes in different land cover types and vegetation growth in response to climate change are largely unknown.Here,we selected land areas with latitudes higher than 40°N as the study area.We compared the land cover type changes and explored relationships between the normalized difference vegetation index(NDVI)values of different land cover types,air temperature,and precipitation from 1982 to 2015 based on a dynamic grid.(2)it’s insufficient to explain vegetation changes based global land cover dataset to account for Arctic vegetation community inhomogeneity.Thus,we filter relevéand process overlay analysis from Global Biodiversity Information Facility,based on vegetation communities in northern latitudes,and get available training data.Finally,we get a new Arctic vegetation atlas between 1982—2020.The result shows overall accuracy is 83.50%between the three subzones of the study area,which is higher than CAVM2019(70%).Owing to Hydrothermal conditions,the vegetation shows a different trend with variable permafrost types.In continuous permafrost areas and where get sufficient precipitation,moss area is growing.However,moss and lichen lived loblolly,with graminoids vegetation invading shrubs on account of total precipitation increased.Graminoids gradually grew into barrens and barren complexes on global warming like carbonate mountain complex and noncarbonate mountain complex.In the non-permafrost zone,extreme events,and human impact lead to some death of forests and shrubs.Overall,forest and shrub areas show dramatically increased.