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Abstract:
Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest
ecosystems. These impacts remain poorly understood at the tree and species level and
across large spatial scales. Here, we investigate the effects of the record-breaking 2018
European heatwave on tree growth and tree water status using a collection of high-temporal
resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding
years, annual stem growth was not consistently reduced by the 2018 heatwave but stems
experienced twice the temporary shrinkage due to depletion of water reserves. Conifer
species were less capable of rehydrating overnight than broadleaves across gradients of soil
and atmospheric drought, suggesting less resilience toward transient stress. In particular,
Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution
dendrometer network was suitable to disentangle the effects of a severe heatwave on tree
growth and desiccation at large-spatial scales in situ, and provided insights on which species
may be more vulnerable to climate extremes.
