Study On The Vegetation Characteristics Of Different Types Of Permafrost In The Greater Khingan Mountains

Vegetation and permafrost are important parts of the ecosystem in cold regions.In the long-term selection process of permafrost environment,vegetation shows suitable vegetation characteristics.With the global warming,the permafrost environment has changed,and the growth characteristics of vegetation have also changed.Permafrost region in the Greater Khingan Mountains is the only high-latitude permafrost region of China,and it is also a typical cold region ecosystem.The ecological environment is fragile and sensitive to global climate change.Meanwhile,China has implemented a natural forest resource protection project in the Greater Khingan Mountains.Under the influence of natural and man-made factors,it is necessary to carry out research on the changes of vegetation characteristics in the Permafrost region of the Greater Khingan Mountains.In this paper,combined with field survey and remote sensing methods,the vegetation community,vegetation remote sensing index and vegetation phenology of different types of permafrost regions in the Greater Khingan Mountains have been studied on the temporal and spatial scales,and the response of vegetation in the permafrost regions of the Greater Khingan Mountains to permafrost degradation has been explored.It is expected to provide a theoretical basis for forest management and enrich the study of ecosystems in cold regions.The main conclusions include:(1)Permafrost region in the Greater Khingan Mountains has been severely degraded due to human disturbance.The thickness of the active layer of permafrost in the nature reserve is significantly smaller than outside the reserve.In areas where the active layer thickness of permafrost is small,the biomass of shrubs and the ratio of diameter at breast height of Larix olgensis are smaller than areas where the thickness of the active layer is large,indicating that permafrost has a certain inhibitory effect on the growth of shrubs and trees.(2)The vegetation coverage in the permafrost region of the Greater Khingan Mountains is at a relatively high level,and with the implementation of the natural forest resource protection project,the growth of vegetation has improved in the past 20 years.The growth status and vegetation coverage of vegetation in the permafrost with isolated taliks are better than those in the predominantly continuous permafrost.In the context of climate change,the ecological environment of the predominantly continuous permafrost is more fragile and more susceptible to the impact of climate change.(3)The time series of NDVI,EVI and SIF can all reflect the seasonal changes of vegetation and can be used to extract vegetation phenological information.SIF is consistent with vegetation photosynthesis and has a stronger physiological basis.Compared with NDVI and EVI,the phenological results extracted by SIF have the start of the growing season later and end earlier,and the length of the growing season is also the shortest.In areas with high vegetation coverage,NDVI suffers from insufficient correction of atmospheric effects and saturation.The spatial pattern of EVI is more consistent with vegetation types.Therefore,EVI has a better monitoring effect on vegetation phenology in permafrost regions of the Greater Khingan Mountains.(4)In the past 20 years,the vegetation phenology parameters have not changed significantly on the scale of the study area.On the pixel scale,only a small part of the change trend of the pixel passed the significance test.Moreover,the number of pixels and the trend of change in the predominantly continuous permafrost are greater than those of the permafrost with isolated taliks,indicating that the predominantly continuous permafrost is more sensitive to global climate change.(5)The average value of SOS in predominantly continuous permafrost is lower than that in permafrost with isolated taliks,and the EOS average in predominantly continuous permafrost is greater than that in permafrost with isolated taliks,indicating that vegetation in predominantly continuous permafrost enters the growing season early and ends the growing season late.The length of the growing season of vegetation in the first region of permafrost is longer than that of the permafrost with isolated taliks.