Abstract
Vegetation phenology and photosynthetic primary production have changed simultaneously over the past three decades, thus impacting the velocity of vegetation greenup (Vgreenup) and withering (Vwithering). Although climate warming reduces the frequency of frost events, vegetation is exposed more frequently to frost due to the extension of the growing season. Currently, little is known about the effect of frost during the growing season on Vgreenup and Vwithering. This study analyzed spatiotemporal variations in Vgreenup and Vwithering in Northeast China between 1982 to 2015 using Global Inventory Modeling and Mapping Studies Normalized Difference Vegetation Index (GIMMS 3g NDVI) data. Frost days and frost intensity were selected as indicators to investigate the influence of frost during the growing season on Vgreenup and Vwithering, respectively. Increased frost days during the growing season slowed Vgreenup and Vwithering. The number of frost days had a greater impact on Vwithering compared to Vgreenup. In addition, Vgreenup and Vwithering of forests were more vulnerable to frost days, while frost days had a lesser effect on grasslands. In contrast to frost days, frost intensity, which generally decreased during the growing season, accelerated Vgreenup and Vwithering for all land cover types. Changes in frost intensity had less of an impact on forests, whereas the leaf structure of grasslands is relatively simple and thus more vulnerable to frost intensity. The effects of frost during the growing season on Vgreenup and Vwithering in Northeast China were highlighted in this study, and the results provide a useful reference for understanding local vegetation responses to global climate change.
Highlights
Global climate change is rapidly altering surface vegetation and impacting the functioning of ecosystems [1]
We investigated changes in frost days and frost intensity during the growing season, and revealed the influence of frost on Vgreenup (Vwithering)
A negative trend in frost intensity was observed during vegetation greenup, whereas it increased in forested areas in the north of the study area during vegetation withering
Summary
Global climate change is rapidly altering surface vegetation and impacting the functioning of ecosystems [1]. A number of studies have demonstrated the earlier start of season (SOS), start of peak season (SOP), and end of peak season (EOP) due to climate change, while end of season (EOS) has been delayed in the northern hemisphere over the past three decades as indicated by both in situ and via remote sensing observations [7,8,9,10,11,12]. The trends of earlier and later phenology have resulted changes of the duration of vegetation greenup (Dgreenup, defined as the time span from SOS to SOP) and withering (Dwithering, defined as the time span from EOP to EOS), which is referred to as an extended vegetation growing season [13]. Changes in the growing season affect the carbon cycle of terrestrial ecosystems, which have complex effects on the growth cycle of vegetation
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