The magnitude and direction of plant species responses to climate change has widespread consequences for trophic interactions, ecosystem services, and our ability to predict the shape of future communities. To date, however, research has focused primarily on documenting species responses without developing a detailed understanding of why some species and communities vary with climate and others do not. Combining expertise from ecologists, phylogeneticists, and climatologists, we will use extensive plant phenology data from experimental and observational studies across North America and Europe to conduct a metaanalysis and develop robust predictors of plant phenology responses and sensitivities to climate change. Our resulting database of phenological studies, their related climate variables, and phylogenetic trees will be, we believe, the most comprehensive data available to study the relationship between climate change and plant species phenological responses. Our comparison of experiments to observational studies will test whether short-term, small-scale manipulations of climate can predict the long-term trends seen on global scales, and should improve the design of future climate manipulation experiments. Additionally, our work will develop new approaches for the use of climate metrics in ecology and inform the designs of government data inventories and citizen science projects. collapse