Coupled decline in growth and fine‐branching signals the onset of drought‐induced European beech mortality
Gerhard Schmied, Dominik Ambs, Luke Bohnhorst, Julia Schmucker, Jill Sekely, Hans Pretzsch, Lars Opgenoorth, Katrin Heer, Stephan Raspe, Torben Hilmers, Richard L. PetersSummary
Severe and recurrent droughts have caused widespread canopy decline and mortality in European forests. Drought‐induced mortality occurs when structural damage and physiological dysfunction impair a tree's ability to recover, yet it remains unclear when trees transition from reversible stress to irreversible vitality loss at the whole‐tree level.
We combined detailed information on fine‐branching architecture derived from terrestrial laser scanning with radial growth data from 174 trees to assess how structural and growth decline relate to drought‐induced mortality in European beech (
Fagus sylvatica
).
We found that European beech trees cross a critical tipping point under drought stress when pronounced declines in fine‐branching and radial growth occur together. Mortality probability increased sharply once relative twig length (= fine‐branching) dropped below
c.
325 m m
−3
and relative growth fell below
c.
7%, equaling a ≥ 75% mortality probability within 3 yr, whereas neither indicator alone reliably captured this transition.
Our results demonstrate that drought‐induced vitality loss in an angiosperm follows distinct trajectories but converges on a critical zone of coupled crown and growth decline that marks an ‘area of no return.’ Linking crown deterioration with growth performance provides a mechanistic early‐warning signal of irreversible vitality loss under intensifying climate extremes.