Vegetation modulates the impact of climate extremes on gross primary production

Milan Flach,Markus Reichstein,Miguel D Mahecha,Fabian Gans,Alexander Brenning,Sebastian Sippel

doi:10.5194/bg-18-39-2021

Abstract

Abstract. Drought and heat events affect the uptake and sequestration of carbon in terrestrial ecosystems. Factors such as the duration, timing, and intensity of extreme events influence the magnitude of impacts on ecosystem processes such as gross primary production (GPP), i.e., the ecosystem uptake of CO2. Preceding soil moisture depletion may exacerbate these impacts. However, some vegetation types may be more resilient to climate extremes than others. This effect is insufficiently understood at the global scale and is the focus of this study. Using a global upscaled product of GPP that scales up in situ land CO2 flux observations with global satellite remote sensing, we study the impact of climate extremes at the global scale. We find that GPP in grasslands and agricultural areas is generally reduced during heat and drought events. However, we also find that forests, if considered globally, appear in general to not be particularly sensitive to droughts and heat events that occurred during the analyzed period or even show increased GPP values during these events. On the one hand, normal-to-increased GPP values are in many cases plausible, e.g., when conditions prior to the event have been particularly positive. On the other hand, however, normal-to-increased GPP values in forests may also reflect a lack of sensitivity in current remote-sensing-derived GPP products to the effects of droughts and heatwaves. The overall picture calls for a differentiated consideration of different land cover types in the assessments of risks of climate extremes for ecosystem functioning.

Highlights

We expect that climate change will lead to increases in frequencies, durations, intensities, and spatial extents of droughts and heatwaves in the decades (Meehl et al, 2000; Olesen and Bindi, 2002; Seneviratne et al, 2012; Coumou and Robinson, 2013; Cook et al, 2015; Zscheischler and Seneviratne, 2017)
Using a global upscaled product of gross primary production (GPP) that scales up in situ land CO2 flux observations with global satellite remote sensing, we study the impact of climate extremes at the global scale
The dichotomy described in the instantaneous response patterns confirms the overall statistics. Events with their centroid in France 2003, Russia 2010, and Germany 2018 all show bidirectional GPP anomalies that coincide with land cover type transitions between predominantly forested land cover and others

Summary

Introduction

We expect that climate change will lead to increases in frequencies, durations, intensities, and spatial extents of droughts and heatwaves in the decades (Meehl et al, 2000; Olesen and Bindi, 2002; Seneviratne et al, 2012; Coumou and Robinson, 2013; Cook et al, 2015; Zscheischler and Seneviratne, 2017). In particular the processes controlling the terrestrial carbon balance, i.e., photosynthesis and respiratory processes as well as fires and, for example, pest-induced mortality, are expected to be affected (Peuelas et al, 2004; Ciais et al, 2005; Vetter et al, 2008; Reichstein et al, 2013; Bastos et al, 2014; Yoshida et al, 2015; Wolf et al, 2016; Brando et al, 2019) (for a recent review see Sippel et al, 2018) Given that these responses represent feedbacks to the coupled climate–ecosystem dynamics, it is important to understand which factors generally influence the magnitudes of such impacts at the global scale. Soil moisture depletion in spring can even enhance carbon losses during summer (Buermann et al, 2013; Sippel et al, 2017a; Buermann et al, 2018)

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Discussion

Conclusion