Abstract
Continuous satellite datasets are widely used in tracking vegetation responses to climate variability. Start of season (SOS), for example, can be derived using a number of methods from the time series of satellite reflectance data; however, various methods often produce different SOS measures which limit the application of satellite data in phenological studies. Therefore, we employed five methods to estimate SOS from the Advanced Very High Resolution Radiometer (AVHRR)/normalized difference vegetation index (NDVI) dataset. Subsequently, we compared the SOS with the ground-based first leaf date (FLD) of 12 deciduous broadleaved plant species at 12 sites of the Chinese Phenological Observation Network (CPON). The results show that the latitudinal patterns of five satellite-derived SOS measures are similar to each other but different from the pattern of ground phenology. For individual methods, the variability of SOS time series is significantly different from ground phenology except for HANTS, Polyfit, and Midpoint methods. The SOS calculated using the Midpoint method showed significant correlations with ground phenophases most frequently (in 47.1% of cases). Using the SOS derived from the Midpoint method, significantly earlier trends in SOS were detected in 50.7% of the natural vegetation area from 1982 to 2006.
Highlights
Phenology, as the study of periodic biological events in the animal and plant world [1], occupies an important position in global change science
We studied the spatial pattern of Start of season (SOS) averaged over five SOS measures in the 1982 to 2006 period
Individual methods often differ in SOS measures, especially in North China
Summary
As the study of periodic biological events in the animal and plant world [1], occupies an important position in global change science. Impacted by recent climate change [4, 5], trends toward earlier plant phenophases in spring have been observed in many places around the world [6, 7]. Such phenological shifts can influence many properties of terrestrial ecosystems [4, 9]. It is reported that plant phenology is tightly coupled with the seasonal cycles of surface carbon and energy balances in boreal forest ecosystems in western Canada [10]. Earlier spring onset in combination with delays in the end of the growing season has resulted in enhanced vegetation growth in the Northern Hemisphere over the past two decades [12]
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