Predicting future forests: Understanding diverse phenological responses in North American temperate forests and globally

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In recent years increasing attention has focused on plant phenology (the timing of recurring life history events such as leafout) as an important indicator of the biological impacts of climate change, as many temperate plants have shifted their timing earlier with increasing temperatures. As data have accumulated, researchers have found a link between phenological responses to warming and plant performance and plant invasions. Such work suggests phenology may not only be a major impact of warming, but a critical predictor of future plant performance. These studies, however, often consider phenology as a singular plant trait---one that may critically influence plant performance and spread but is not tied to other major traits. In contrast plant phenology could be considered as one of many correlated traits making up a plant's trait syndrome. I suggest progress can come from explicitly considering phenology as a critical plant trait correlated with other major functional traits.Previous research highlights a trade-off where earlier phenologies are associated with a suite of traits related to rapid return on investment, but lower competitive ability, while species leafing and flowering later show the reverse. This axis makes sense when considering how stress, disturbance and competition vary across the growing season in temperate systems: early in the season when abiotic stress and disturbance are high (e.g., frosts etc.), but competition low, an early-flowering, rapid growth, and comparatively low-investment strategy allows species to grow and reproduce quickly before periods of strong competition begin. This research program will test for evidence of this trade-off across >100 woody species and how it relates to plant performance with climate change. Such a trade-off would mean phenology's strong links to invasions and performance with climate change may be only one piece of a larger story of how a correlated set of traits are promoted by warming, and contribute to the lab's larger goal of understanding how plant communities assemble and dis-assemble with climate change. The proposed work combines local, regional and global scale approaches to examine how phenology fits within a functional trait framework then tests for the relative roles of phenology and other major plant traits in driving plant performance. In particular this proposal will address the following questions: (1) How can we best predict woody species phenological responses to climate change considering the three major cues of spring warming temperatures, winter chilling temperatures and daylength? (2) What is the relationship between phenology and performance in temperate woody species? (3) How do major functional traits relate to plant phenological responses to climate? (4) What is the relative importance of phenology versus other functional traits in predicting plant performance responses to climate change?