Depicting the Asymmetries of Vegetation Phenology over Northeast China Using Remote Sensing NDVI Dataset

Vegetation phenology is an important ecological indicator for global climate change.Plant greenup phenology in the spring time has been well studied，whereas autumn phenology and its asymmetry with spring phenology still remain unclear.Here，the GIMMS NDVI3g dataset for Northeast China was applied to extract the key phenological parameters during plant growth process，then three phenological asymmetry indices were defined according to the difference between greenup rate and senescence rate(AsyR)，growth length in spring and autumn(AsyL)，mean vegetation greenness index in spring and autumn(AsyV).First，plant growing curve was fitted with double logistic function and the phenological parameters was calculated.Second，the spatiotemporal pattern of asymmetry indices was explored.The results indicate that the three phenological asymmetry indices show a significant interannual variability and a time cycle of around ten years.The direction of amplitude for AsyV and AsyL was opposite with that of AsyR.Three indices could depict the phenological asymmetries from various perspectives and have a degree of uncertainty.The landscape pattern for AsyV and Asy R is similar.AsyV and AsyR show a capability of distinguishing cropland and natural vegetation cover.AsyL reflects a complex spatial distribution.Phenological asymmetries reveal that coniferous forest and broad-leaved forest present a dominant control of senescence vegetation activities.These natural vegetation commonly show a growth feature of rapid growth in spring and slow decrease in autumn.Cropland exhibits a slowly growing rate in spring and a rapid decrease in autumn.Phenological asymmetry is not significant in grassland area.Phenological asymmetry could enhance our knowledge on ecosystem carbon sink.In a practical way，phenological asymmetry could serve as a useful tools in vegetation type classification，agricultural investigation and plant ecosystem management.