Abstract
Monitoring the phenological responses of deciduous forests to climate is important, due to the increasing frequency and intensity of extreme climatic events associated with climate change and global warming, which will in turn affect vegetation seasonality. We investigated the spatiotemporal patterns of the response of deciduous forests to climatic anomalies in the Northern Hemisphere, using satellite-derived phenological metrics from the Copernicus Global Land Service Leaf Area Index, and multisource climatic datasets for 2000–2018 at resolutions of 0.1°. Thereafter, we assessed the impact of extreme heatwaves and droughts on this deciduous forest phenology. We assumed that changes in the deciduous forest phenology in the Northern Hemisphere for the period 2000–2018 were monotonic, and that temperature and precipitation were the main climatic drivers. Analyses of partial correlations of phenological metrics with the timing of the start of the season (SoS), end of the season (EoS), and climatic variables indicated that changes in preseason temperature played a stronger role than precipitation in affecting the interannual variability of SoS anomalies: the higher the temperature, the earlier the SoS in most deciduous forests in the Northern Hemisphere (mean correlation coefficient of −0.31). Correlations between the SoS and temperature were significantly negative in 57% of the forests, and significantly positive in 15% of the forests (p < 0.05). Both temperature and precipitation contributed to the advance and delay of the EoS. A later EoS was significantly correlated with a positive Standardized Precipitation Evapotranspiration Index (SPEI) at the regional scale (~30% of deciduous forests). The timings of the EoS and SoS shifted by >20 d in response to heatwaves throughout most of Europe in 2003, and in the United States of America in 2012. This study contributes to improve our understanding of the phenological responses of deciduous forests in the Northern Hemisphere to climate change and extreme climate events.
Highlights
Interest in understanding the interactions between phenology and climate has increased over the past few decades [1], because vegetation phenology plays an important role in balancing biogeochemical cycles, such as the exchange of water, energy, and carbon [2,3,4,5]
When analyzing the influence of drought on vegetation, we found that Standardized Precipitation Evapotranspiration Index (SPEI) calculated using timescales between 1 and 3 months was the best correlated with the timings of the start of the season (SoS) and end of the season (EoS) in > 50% of the pixels (Table S3)
Our results indicated that anomalies of temperature and precipitation controlled the changes in phenological metrics in the deciduous forests, consistent with previous studies [2,101]; the anomalies of SoS were strongly associated with the changes in mean preseason temperature, so this climatic variable may have been the main cause of the advance or delay in the start of the growing season, affecting 72.1% of the study area (p < 0.05)
Summary
Interest in understanding the interactions between phenology and climate has increased over the past few decades [1], because vegetation phenology plays an important role in balancing biogeochemical cycles, such as the exchange of water, energy, and carbon [2,3,4,5]. Investigating the interactive effects of temperature and precipitation on phenology, in order to understand and anticipate the effects of climate change on vegetation, is crucial [12]. Many previous studies have investigated the changes in vegetation phenology as a result of climate change and the associated global warming [13,14,15,16]. In this sense, the analysis of the sensitivity of vegetation to hydroclimatic anomalies is increasingly studied [1,17]—especially the effects of temperature on Remote Sens.
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