Slow sapling recovery leads to mortality rather than acclimation

Mirela Beloiu, Biogeography, Universität Bayreuth, Bayreuth, Germany, Reinhold Stahlmann and Carl Beierkuhnlein, Biogeography, University of Bayreuth, Bayreuth, Germany

Background/Question/Methods
Resilience is a key concept in ecology and describes the capacity of an ecosystem to reduce the impact of a disturbance, recover from it, and return to a stable state. An essential aspect of resilience is recovery. However, it is still questionable whether species with slow recovery are more susceptible to mortality or whether this reflects an acclimation, optimizing survival in the long term. Forests are one of the ecosystems most vulnerable to disturbances, such as droughts. Here, we combine field measurements with remote sensing techniques to assess damages by the 2018 drought and the recovery and mortality patterns after it for saplings and mature trees. We measured 1606 saplings from 174 plots across central Germany over three years.
Results/Conclusions
Our results indicate that recovery time after a disturbance increases with tree ontogeny. Fast recovery is correlated with saplings’ survival whereas low recovery is correlated with mortality. Mature tree recovery was highest in coniferous, followed by deciduous, and mixed forests. In contrast to large trees, saplings face more favorable conditions under drought. Nevertheless, saplings on shallow soils and previously moist sites are more vulnerable to drought events. Whereas mature trees are particularly vulnerable to water shortages combined with an increase in temperature. Mature trees showed long-lasting drought-induced effects on crown structure compared to saplings from the same sites. These findings highlight that saplings and mature tree recover differently after a drought event, which might increase their vulnerability to future climate changes and lead to changes in forest productivity, carbon cycling, and their biodiversity.