Tree architecture modulates the trends in greenness and water content of European forest canopies

Abstract The ongoing rapid changes in climate pose significant pressures on forests’ health and growth with modalities that are still poorly understood 1–3 . Trees’ structural properties like tree height, leaf and root biomass, result from the interplay between plant physiology and key environmental factors like temperature and water. On the other hand, the combination of these structural properties and site characteristics controls the functioning of trees and their sensitivity to environmental stressors. The unbalance between tree architecture and environmental conditions driven by climate change may therefore affect plant growth, vulnerability and mortality, ultimately affecting the stability of the terrestrial carbon cycle and the mitigation potential of land-based climate solutions 4 . Here we use satellite data and machine learning to assess the response of European forests to changing climate over 2001-2020. We show that tree architecture, topography and soil characteristics largely control the recent trend in forest greenness and dryness. Specifically, our results show that tree height and the vertical distribution of leaves have a strong effect on the canopy decline observed in large areas of Europe, with toller trees having leaves close to the top that show browning and drying signals. In addition, we demonstrate that the negative impact of recent climate trends is exacerbated on south-facing slopes and in nutrient-rich soil with high bulk density. These architectural and environmental controls of the trees’ response to climate are currently not accounted for in vegetation models, which therefore poorly represent the recent pattern of forest dieback 5,6 , and may therefore underestimate the risks of natural disturbances and tree mortality. These findings unveil the drivers of the worrying trends in EU forest conditions. In parallel, they offer valuable insights for the development of climate-effective practices for the management of EU forests under the pressure of climate change.