Abstract
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.
Highlights
Substantial climate warming has occurred during the 20th century, especially during the last 30 years of the century (IPCC 2001a, b)
The forests in mid latitudes manifested high chlorophyll contents from April to September, while tundra in high latitudes only showed the high value in summer
This study detects a suite of phenological variables of ecoregions for the North-South Transect of Northeast Asia using multi-temporal composites of a remote sensingbased chlorophyll index
Summary
Substantial climate warming has occurred during the 20th century, especially during the last 30 years of the century (IPCC 2001a, b). There is a growing consensus that arctic regions will experience marked changes in precipitation, temperature, and the timing of seasonal climate events (Bradley et al 1993). It is recognized that a vegetation index time-series carries useful information about seasonal vegetation development and that this information will aid analyses of the functional and structural characteristics of the land cover (Jönsson and Eklundh 2002). Temporal vegetation information such as moisture and carbon dioxide on a global scale is important for strengthening our current knowledge concerning global cycles of matter (Rosenqvist et al 2000). Because remotely sensed data which comprise the vegetation index is gathered almost daily and covers large areas, it has been widely used for monitoring spatial gradients and the intra-seasonal dynamics of vegetation, especially in large and remote regions (Gutman et al 1994; Jia et al 2002)
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