Tree crown metrics as indicators for drought stress resistance?

The crown of a tree determines current growth and reflects past growth patterns, competition and ecological stress factors such as drought, nutrient deficiency, or competitive pressure. In the context of climate change, assessing the acclimatization potential of trees to drought stress is crucial. This study investigates the relation of crown morphology with the basal area increment of 151 Norway spruces (Picea abies L. Karst), 151 Scots pines ( Pinus sylvestris L.), 217 European beeches ( Fagus sylvatica L.) and 61 oaks ( Quercus petraea (Matt.) Liebl./ Quercus robur L.) in southern Germany. Using terrestrial laser scans, eleven metrics describing the crown and competition were calculated from the tree point clouds. We linked these with tree-ring widths of increment cores to model basal area increment and relative growth decline during the Central European drought period 2015–2022. Using correlation analyses, we investigate the strength of different crown traits' association with growth over periods of different lengths (1–30 years). We found that trees develop species-specific crowns exhibiting temporally differentiated structural memory (i). Crown morphology is thus not only functional but also retrospectively interpretable. Furthermore, we found a considerable influence of various crown metrics on the drought stress response of trees (ii). However, the nature of the influence is highly differentiated and suggests a nonlinear stress response and trade-offs in acclimation. Our study highlights the relevance of crown morphology in drought response and provides a basis for further investigations into tree resilience and forest acclimation. • Species-specific crown metrics are significantly associated with long-term growth patterns. • Several crown metrics correlate with drought-induced growth decline across species. • Trees exhibit non-linear and species-specific growth responses to drought conditions. • Crown traits beneficial under normal conditions may become disadvantageous during drought.