Characterizing Spatial-Temporal Variations in Vegetation Phenology over the North-South Transect of Northeast Asia Based upon the MERIS Terrestrial Chlorophyll Index

This study attempted to establish a broad regional phenological pattern for Northeast Asia using time-series data of the satellite measured index of terrestrial chlorophyll content (MERIS Terrestrial Chlorophyll Index) from 2003 to 2007. A suite of phenological variables were extracted from 4 integral seasons of time-series Medium Resolution Imaging Spectrometer (MERIS) Terrestrial Chlorophyll Index (MTCI) of World Wildlife Fund (WWF) ecoregions smoothed by an asymmetric Gaussian model. In this study, spatial variation with latitude was observed for the chlorophyll content and phenological variables for natural vegetation across north-south transect of northeast Asia (NSTNEA). The onset of greenness for most ecoregions followed a latitudinal pattern with an earlier onset of greenness at lower latitudes. In general, the length of growing season was higher at lower latitudes. For forests in NSTNEA, the average maximum MTCI value and range of MTCI value at lower latitudes were significantly larger than that at higher latitudes during the study period. In addition, the cumulative CV showed a declining trend with an increase in latitude overall. Our findings suggest that although precipitation plays a promoting role, temperature is still the dominant factor in vegetation phenological period at high latitudes.