Crown die-back of peri-urban forests after combined heatwave and drought was species-specific, size-dependent, and also related to tree neighbourhood characteristics

The Rhine River valley of Germany has been facing recurrent and intense spells of drought and heatwaves threatening the health of trees in peri-urban forests. Crown damage intensified by climate change accelerates tree mortality, threatening its ecological, economic, and social benefits; however, the pattern of crown die -back in peri-urban forests remained unclear. We performed a field inventory to estimate the crown die -back of 2578 trees of 51 species from 68 randomly selected peri-urban forest plots in Karlsruhe region on the right bank of the Rhine, after the catastrophic summer heatwave and drought of 2018. We related crown die -back to speciesspecific drought tolerance, wood anatomical traits, tree size, canopy surface temperature, tree density, Shannon's diversity and Gini coefficient for tree height. Regression results indicate that small -size trees were found to be more susceptible to canopy damage than large trees, with a 1 -meter increase in tree height associated with a 0.8 % reduction in crown die -back. This size -dependent process is also species -specific. Among the 12 species with significant (p < 0.05) linear relationship between height and die -back, 9 species demonstrated negative correlations and 3 species showed positive relationships. Species tolerant to drought or cavitation (e.g., trees with diffuse porous xylem, 21 species) had significantly lower crown dieback. For example, with a 1 -point -scale Contents lists available at ScienceDirect Science of the Total Environment