Observational evidence of legacy effects of the 2018 drought on a mixed deciduous forest in Germany

Abstract

Forests play a major role in the global carbon cycle, and droughts have been shown to explain much of the interannual variability in the terrestrial carbon sink capacity. The quantification of drought legacy effects on ecosystem carbon fluxes is a challenging task, and research on the ecosystem scale remains sparse. In this study we investigate the delayed response of an extreme drought event on the carbon cycle in the mixed deciduous forest site ’Hohes Holz’ (DE-HoH) located in Central Germany, using the measurements taken between 2015 and 2020. Our analysis demonstrates that the extreme drought and heat event in 2018 had strong legacy effects on the carbon cycle in 2019, but not in 2020. On an annual basis, net ecosystem productivity was $$\sim 16\,\%$$ ∼ 16 % higher in 2018 ($$\sim 424\,{\hbox {g}_{\text {C}}}\hbox {m}^{-2}$$ ∼ 424 g C m - 2 ) and $$\sim 25\,\%$$ ∼ 25 % lower in 2019 ($$\sim 274\,{\hbox {g}_{\text {C}}}\hbox {m}^{-2}$$ ∼ 274 g C m - 2 ) compared to pre-drought years ($$\sim 367\,{\hbox {g}_{\text {C}}}\hbox {m}^{-2}$$ ∼ 367 g C m - 2 ). Using spline regression, we show that while current hydrometeorological conditions can explain forest productivity in 2020, they do not fully explain the decrease in productivity in 2019. Including long-term drought information in the statistical model reduces overestimation error of productivity in 2019 by nearly $$50\,\%$$ 50 % . We also found that short-term drought events have positive impacts on the carbon cycle at the beginning of the vegetation season, but negative impacts in later summer, while long-term drought events have generally negative impacts throughout the growing season. Overall, our findings highlight the importance of considering the diverse and complex impacts of extreme events on ecosystem fluxes, including the timing, temporal scale, and magnitude of the events, and the need to use consistent definitions of drought to clearly convey immediate and delayed responses.

Forest growth resistance and resilience to the 2018-2020 drought depend on tree diversity and mycorrhizal type

“…We found strong declines in growth during the 2018-2020 drought event for the majority of the investigated tree communities (Figure 1). Other studies that assessed the impact of the 2018-2020 drought on forests have consistently reported signs of tree drought stress, reduced growth and increased tree mortality, both during and after the drought period (Buras et al, 2020;Obladen et al, 2021;Pohl et al, 2023;Schnabel et al, 2022;Schuldt et al, 2020;Senf et al, 2020). While our reported growth reduction by 36.8 % lines up with the finding of an earlier study by Thom et al, 2023, that reported a 41.3% reduction during the 2018-2020 drought, it should be kept in mind that our reductions are biologically even higher, because we expect an ontogenetic increase (Pretzsch, 2020).…”

“…The growth responses of the tree communities at our site seemed to closely mirror the meteorological drought patterns, with the lowest growth rate in 2018, followed by 2019 and 2020. However, contrary findings from other studies point to 2019 as the year with the strongest growth reduction (Pohl et al, 2023;Salomón et al, 2022;Schnabel et al, 2022), attributed to the legacy effects of the 2018 drought (Anderegg et al, 2015;Kannenberg et al, 2020;Schnabel et al, 2022). Such drought legacies might be caused by diminished reserves of non-structural carbohydrates and altered carbon allocation, favouring the canopy and root system instead of radial stem growth (Hartmann & Trumbore, 2016;Brunner et al, 2015;Kannenberg et al, 2019).…”

Assessing impacts of alternative land use strategies on water partitioning, storage and ages in drought‐sensitive lowland catchments using tracer‐aided ecohydrological modelling

“…However, EcH 2 O-iso allows vegetation dynamics to be assessed (Douinot et al, 2019), and temporal changes in soil properties associated with land use change need to be incorporated (e.g., Poorter et al, 2021). In this regard, recent forest productivity changes associated with drought conditions could be used to better understand the complex lag effects of droughts on forests physiology and water cycling and incorporate this behaviour in models (e.g., Pohl et al, 2023).…”

Deterioro de ecosistemas y paisajes: Lo último al 2023

“…La sequía extrema como causa de deterioro del ecosistema tiene impactos positivos en el ciclo del carbono al comienzo de la temporada de vegetación, pero impactos negativos a finales del verano, mientras que los eventos de sequía a largo plazo tienen impactos generalmente negativos durante toda la temporada de crecimiento (Pohl et al, 2023).…”