Variation in responsiveness of woody plant leaf out phenology to anomalous spring onset

Abstract Timing of leaf out in woody plants is being affected by global climate change, with cascading effects on associated organisms and ecosystem processes. However, the timing and responsiveness of this important phenological event are not well understood, especially in relation to the geographic origin of species and populations. This study assessed the effect of anomalous spring warming on leaf out timing for woody plant species and individuals from a range of taxa and geographic origins. Timing of leaf out was assessed across 4 years (2011–2014) for 478 plants, representing 96 species and 21 genera, planted together in a common environment at The Morton Arboretum, Lisle, Illinois, USA. An anomalously warm spring in 2012 strongly affected leaf out timing, advancing mean leaf out date for every species by an average of 31 days across all individuals. Responsiveness was related to species traits, as species classified as early‐successional, with diffuse‐porous wood anatomy, or with a weak chilling requirement were much more responsive. There was strong variation among individuals within a species in leaf out timing and responsiveness. These patterns were somewhat related to geographical origin of the individual, but were not consistent among species or genera. High responsiveness of leaf out to anomalous spring warming, which is forecasted to be more common with global climate change, could have important implications for climate change adaptation, assisted migration, and ecological interactions. Chilling requirements may have limited responsiveness for some species, which could affect competitive dynamics within plant communities. Through such interactions and direct effects on woody plant species, variation in spring leaf out phenology will likely affect biodiversity and functioning in many ecosystems.