Abstract
The accumulation of heat and moderate precipitation are the primary factors that are used by grasslands to trigger a green-up date. The accumulated growing degree-days (AGDD) requirement over the preseason is an important indicator of the response of grassland spring phenology to climate change. This study adopted the Normalized Difference Phenology Index (NDPI), which derived from the Moderate Resolution Imaging Spectroradiometer (MODIS), to extract annual green-up dates in the Hulun Buir grassland in China between 2001–2015. Our analysis indicated that the range (standard deviation) and trend for the green-up date were DOY (day of year) 104 to DOY 144 (10.6 days) and −2.0 days per decade. Nine point two percent of the study area had significant (p < 0.05) changes in AGDD requirements. The partial correlations between the AGDD requirements and chilling days (67.04%, pixels proportion) were negative and significant (p < 0.05). The partial correlations between the AGDD requirement and precipitation (28.87%) were positive and significant (p < 0.05). Finally, the partial correlation between the AGDD requirement and insolation (97.65%) were positive and significant (p < 0.05). The results of this study could reveal the response of vegetation to climate warming and contribute to improving the phenological mechanism model of different grassland types in future research.
Highlights
Though a higher accumulated growing degree-days (AGDD) was required in warm steppe, the green-up date was earlier than other cold grassland-type areas
Our analysis showed that 90.2% of the regional AGDD requirement did not change significantly; this proportion was the same as that described previously for the change in AGDD requirement on the Qinghai-Tibet
We found that the increase in heat requirement for grassland vegetation was positively correlated with precipitation
Summary
Plant phenology aims to investigate the interrelationships between cyclical plant phenological phenomena and environmental conditions [1,2]. Phenological events reflect a combination of intrinsic factors of plants (genetic) and environmental impacts. Since the avoidance of late spring frost damage and early autumn cold events are very important for the survival of plants, timely green-up is essential [3]. Changes in the phenological phenomena of vegetation that are caused by global climate changes lead to constant
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