Remote Sensing Monitoring Of Forest Phenology In Guizhou And Its Response To Climate Change

Vegetation phenology can provide a lot of information about global climate change and the ensuing changes in the plant cycle,thus it is considered to be a sensitive indicator for climate change.Phenology study has important research significance in areas such as ecology,global change,and agroforestry management.Looking through the remote sensing research of vegetation phenology in China,most of the research areas are concentrated in the mid-latitude temperate vegetation area,and the research on the climate change response of vegetation phenology in the subtropical and tropical areas is still insufficient.There are more studies on crops,deciduous forests and grasslands,and less exploration on evergreen forests.Based on this,combined with ground observation data,this study explored the amplitudeof impact of climate change on forest phenology in subtropical evergreen forests in Guizhou province over the past 15 years.The purpose of this study is to enrich the remote sensing methods in phenology research in tropical regions besides the temperate area,and further reveal the pattern of the forest phenology in response to climate change.The conclusions were summarized below:(1)The three methods of A-G fitting,D-L fitting and S-G filtering of TIMESAT showed little difference in the visual assessment of the NDVI time series curve characteristics for the same vegetation type in the study area.For the forest vegetation,the S-G filter preserved the details of the time series better than the other filters,and it was the best way for the fidelity of the original high quality NDVI time series data among different forest vegetations.S-G filter was suitable for the remote sensing parameter extraction of forest vegetation in Guizhou province.(2)For the spatial pattern of the multi-year averaged phonological dates,the start of the growing season(SOS)of forest vegetation in Guizhou was mainly from early March to mid-April,delayed from the east to the west during 2001 to 2015.The end of the growing season(EOS)was generally late in late november,delayed from the middle towards both the east and the west.The length of the growing season(LOS)was mainly concentrated in 255-273 days,shortened from the east to the west.(3)For the relationship between the multi-year average phenologyand topography,the altitude influenced the distribution of forest phenology more than the slope,and the responses of different forest types to elevation were different.With the increase of altitude,the postponed extent of SOS from large to small in the four types of forests was shrub forest > evergreen coniferous forest > deciduous broad-leaved forest > evergreen broad-leaved forest;EOS all occurred ahead of schedule,but non-significantly.The shortening extent of LOS from large to small was shrubland > evergreen coniferous forest > deciduous broad-leaved forest > evergreen broad-leaved forest.(4)With regard to the interannual trends of forest phenology,the general trends of forest phenology in Guizhou province during 2001 to 2015 were all slightly fluctuating,but the spatial variation of the trends was obvious,while phenology of different forest types had different trends.On the overall trend,both SOS and EOS showed non-significant delaying;LOS showed a non-significant shortening trend.In terms of the spatial distribution of changes,SOS and EOS were delayed in the middle,advanced in the east and the west;LOS was shortened from west to east.The phenological trends in different forest types indicated different characteristics.The SOS of evergreen broad-leaved forests and deciduous broad-leaved forests showed significantly delaying,but the SOS of evergreen coniferous forests and shrubs showed advancing trend.Except for the evergreen broad-leaved forest,the EOS of the deciduous broad-leaved forest,the evergreen coniferous forest and the shrubbery showed delaying trend.The LOS of evergreen broad-leaved forest and deciduous broad-leaved forest showed significantly shortening trend,the evergreen coniferous forests and shrubs showed significantly extending trend.(5)The phenology of different forest types showed different responses to temperature and precipitation,but overall,the impact of precipitation on the phenology forest was greater than the temperature.Pre-season rainfall,especially in winter and spring,was the main climatic factor affecting forest phenology in Guizhou province.Drought in winter and spring delayed the SOS in the development of evergreen broad-leaved forest and deciduous broad-leaved forest,and shortened their growing season length in the case of little change in autumn phenology.The increase of precipitation in the winter and spring,combined with the slight increase in temperature in the autumn,led to the advancement of spring phenology in the development of evergreen coniferous forests and shrubs,and delayed in the autumn phenology,thus extended their growing season.