Résumé
Concerns are rising about the capacity of species to adapt quickly enough to climate change. In long-lived organismssuch as trees, genetic adaptation is slow, and how much phenotypic plasticity can help them cope with climatechange remains largely unknown. Here, we assess whether, where and when phenological plasticity is and will beadaptive in three major European tree species. We use a process-based species distribution model, parameterizedwith extensive ecological data, and manipulate plasticity to suppress phenological variations due to interannual, geo-graphical and trend climate variability, under current and projected climatic conditions. We show that phenologicalplasticity is not always adaptive and mostly affects fitness at the margins of the species’ distribution and climaticniche. Under current climatic conditions, phenological plasticity constrains the northern range limit of oak and beechand the southern range limit of pine. Under future climatic conditions, phenological plasticity becomes stronglyadaptive towards the trailing edges of beech and oak, but severely constrains the range and niche of pine. Our resultscall for caution when interpreting geographical variation in trait means as adaptive, and strongly point towards spe-cies distribution models explicitly taking phenotypic plasticity into account when forecasting species distributionunder climate change scenarios.