Peak season plant activity shift towards spring is reflected by increasing carbon uptake by extratropical ecosystems

Abstract

Climate change is lengthening the growing season of the Northern Hemisphere extratropical terrestrial ecosystems, but little is known regarding the timing and dynamics of the peak season of plant activity. Here, we use 34-year satellite normalized difference vegetation index (NDVI) observations and atmospheric CO concentration and δ C isotope measurements at Point Barrow (Alaska, USA, 71°N) to study the dynamics of the peak of season (POS) of plant activity. Averaged across extratropical (>23°N) non-evergreen-dominated pixels, NDVI data show that the POS has advanced by 1.2 ± 0.6 days per decade in response to the spring-ward shifts of the start (1.0 ± 0.8 days per decade) and end (1.5 ± 1.0 days per decade) of peak activity, and the earlier onset of the start of growing season (1.4 ± 0.8 days per decade), while POS maximum NDVI value increased by 7.8 ± 1.8% for 1982-2015. Similarly, the peak day of carbon uptake, based on calculations from atmospheric CO concentration and δ C data, is advancing by 2.5 ± 2.6 and 4.3 ± 2.9 days per decade, respectively. POS maximum NDVI value shows strong negative relationships (p < .01) with the earlier onset of the start of growing season and POS days. Given that the maximum solar irradiance and day length occur before the average POS day, the earlier occurrence of peak plant activity results in increased plant productivity. Both the advancing POS day and increasing POS vegetation greenness are consistent with the shifting peak productivity towards spring and the increasing annual maximum values of gross and net ecosystem productivity simulated by coupled Earth system models. Our results further indicate that the decline in autumn NDVI is contributing the most to the overall browning of the northern high latitudes (>50°N) since 2011. The spring-ward shift of peak season plant activity is expected to disrupt the synchrony of biotic interaction and exert strong biophysical feedbacks on climate by modifying the surface albedo and energy budget.

Acceleration of global vegetation greenup from combined effects of climate change and human land management

“…The comparison between global Vgreenup, Dgreenup and Agreenup indicates that the high spatial and interecosystem heterogeneity of Vgreenup is more determined by the high spatial variation in Agreenup, while the temporal dynamics of Vgreenup are directly controlled by both changes in Dgreenup and Agreenup. This is consistent with recent findings that trends toward an earlier SOP and peak season plant activity shift toward spring co-occurred with increases in vegetation productivity (as represented by NDVI) in mid-and high-latitudes of the NH (Gonsamo et al, 2017;Xu et al, 2016). However, the fact that trends in SOP and productivity are of opposite direction does not a priori cause a change in Vgreenup as it depends on the magnitude and statistical strengths of the trends in Dgreenup (the difference of SOP and SOS) and Agreenup respectively (Wang & Fensholt, 2017).…”

Changes in timing of seasonal peak photosynthetic activity in northern ecosystems

“…It also may reduce the observed DOY Pmax sensitivity to warming (Smith, Malyshev, Shevliakova, Kattge, & Dukes, 2016). Nevertheless, we believe that the proposed DOY Pmax framework and its changes are valid because of multiple evidence from independent datasets in this work (Figure 3 and Figure S3) and previous studies (Buitenwerf et al, 2015;Gonsamo et al, 2018;Rotenberg & Yakir, 2010).…”

Alpine grassland plants grow earlier and faster but biomass remains unchanged over 35 years of climate change

“…Plant growth patterns (i.e., phenology and growth rate) respond to climate variation (Jonas et al 2008;Wingler & Hennessy 2016) and have an important role in regulating Earth's climate because they drive seasonal land-atmosphere exchange of carbon, water and energy (Wang et al 2011;Buitenwerf et al 2015;Xia et al 2015). Plant growth patterns also influence the ability of plant communities to provision animals with habitats and food resources (Hegland et al 2009;Gonsamo et al 2018).…”