Study On The Evolution Process And Vegetation Phenology Response Of The Zoige Alpine Wetland

Zoige Alpine Wetland is located in the eastern part of the Qinghai-Tibet Plateau and the sensitive area of climate change in China.It is an important ecological security barrier in China and even Asia.It is rich in peat resources and is one of the largest peat storage areas in China.It has extremely high ecosystem service value and creates a unique living environment for many rare wild animals and plants.Against the background of global climate change and the accelerating socio-economic development,Niuyue Lake has dried up and disappeared,swamps have shrunk,degraded,and the number of patches has decreased.Therefore,determining the development status of Zoige wetland and realizing effective monitoring of wetland degradation are the prerequisites for ensuring the rational use and efficient restoration of wetland.In this study,based on Landsat TM / OLI data,the land use / cover types of the study area were classified in 7 phases from 1990 to 2018.Based on the rules of wetland evolution in the study area,we use the PNTI index model to evaluate the evolution process of alpine wetlands,and make recommendations for the key restoration types and restoration areas of wetlands.The research used MODIS NDVI and GIMMS NDVI as data sources,based on TIMESAT 3.2 software to extract LSP parameters in the study area,and studied the spatial differentiation of vegetation phenology and the influence factors of time changes.Finally,we explored the indication effect of vegetation phenology on the evolution of alpine wetlands.The specific results are as follows:(1)Wetlands in Zoige County are concentrated in flat and low-lying areas.Wetlands have been decreasing from 1995 to 2010.After 2010,it gradually improved to the area proportion level in 1990,but there are still differences in wetland composition.The decrease in wetlands is mainly due to the shrinkage of swamps,which have shifted to swampy meadows and even alpine meadows.Swamps should be the focus of wetland restoration in this region.(2)The areas where wetland degradation and evolution have been more severe in the past 30 years are Jumang Ranch,Dazasi Town and Tangke Town in the south-central of Zoige County.The evolution path is water ? swamp ? swampy meadow ? alpine meadow.The high altitude of the wetland is characterized by thin air and cold climate,which is the internal reason for the high vulnerability of the ecosystem;increased human disturbance and climate warming are the external conditions for itsdegradation and evolution.Exploring the leading factors of wetland degradation in the area of degradation evolution is the prerequisite for formulating suitable wetland restoration strategies.(3)Spatial and temporal changes of vegetation phenology:In terms of inter-annual change,none of the four phenological parameters showed a significant change trend in the entire study area from 1990 to 2018,and the areas that passed the significance test accounted for up to 21.6%.In terms of spatial distribution,there are obvious regional characteristics in the phenological period.Except for the eastern forest area,the SOS and the POM show the distribution characteristics of “early south and late north”,and the EOS and LOS show “central early(short)and large peripheral(long)" distribution.The spatial differentiation of vegetation phenology is related to altitude and vegetation factors.(4)Temperature is the main factor affecting phenological changes.The rise of the average temperature in that month ushered in early spring,which made the wetland vegetation return SOS earlier.The increase in temperature at the beginning of vegetation increased the EOS of alpine meadows and swampy meadows.The average temperature in September(one month before the season)increased,and the EOS of marsh vegetation was delayed.At the same time,the rising temperature in early autumn can prolong the LOS.The temperature rise in June(one month before the season)made the POM earlier.(5)SOS and EOS are sensitive to the direction of wetland evolution.Vegetation phenology observation indicates the development of the wetland.Effective combination of natural processes and engineering measures can realize timely updating and improvement of wetland protection and restoration strategies.