Impact of Drought on Forest Biosphere-Atmosphere Interactions

Drought stress in forests has been increasing with climate warming, both through reduced soil water availability and increased atmospheric water demand (vapor pressure deficit). The consequences are enhancing (i.e. positive) temperature feedbacks, increased tree mortality and shifts in species composition. This is concerning because forests contribute to mitigate excessive surface temperatures and increases in atmospheric CO₂ concentrations. While drought stress-related declines in photosynthesis are well established, important questions remain regarding (i) changes in respiration, (ii) compensating effects of understory vegetation, (iii) attenuating (i.e. negative) forest-atmosphere feedbacks, and (iv) small-scale processes (i.e. at soil, leaf or tree-level) that also emerge at the ecosystem scale (Wankmüller et al. 2024).

Here we present an overview on the current knowledge of drought impacts on forest biosphere-atmosphere interactions (Wolf & Paul-Limoges 2023), recent evidence for the potential of understory (i.e. below-canopy) eddy-covariance flux measurements (Wolf et al. 2024), and the results of an ongoing drought manipulation experiment using paired (i.e. drought-stressed and irrigated) eddy-covariance flux towers to measure understory biosphere-atmosphere interactions at the Pfynwald forest in Switzerland.  

Finally, we will discuss the challenges and perspectives for scaling fluxes of carbon, water and energy from tree to ecosystem scale using a combination of established and novel in situ measurements.

 

References

Wolf S & Paul-Limoges E (2023) Drought and heat reduce forest carbon uptake. Nature Communications 14: 6217 (https://doi.org/10.1038/s41467-023-41854-x)

Wolf S, Paul-Limoges E, Sayler D, Kirchner JW (2024) Dynamics of evapotranspiration from concurrent above- and below-canopy flux measurements in a montane Sierra Nevada forest. Agricultural and Forest Meteorology 346: 109864 (https://doi.org/10.1016/j.agrformet.2023.109864)

Wankmüller FJP, Delval L, Lehmann P, Baur MJ, Cecere A, Wolf S, Or D, Javaux M, Carminati A (2024) Global influence of soil texture on ecosystem water limitation. Nature 635(8039): 631–638 (https://doi.org/10.1038/s41586-024-08089-2)