COS 132-3 - The relationships between functional traits and budburst phenology of woody plants across North America

Abstract: Woody plant species vary considerably in their spring phenologies, ranging from early leafing understory species at the start of the growing season, to later developing canopy species. Such differences in species temporal niches are important in determining the abiotic environments experienced, as well as the intensity and diversity of biotic interactions. Species that budburst early in the season, for example, are at a greater risk of frost damage, but later budbursting species experience competition for soil resources and light. The varying selective pressures that this phenological gradient create may also lead to variation in other functional traits. We might expect early budbursting species to produce less costly tissue and express traits than infer more acquisitive growth. In contrast, later developing species experience a more favourable abiotic environment, but must possess traits that allow them to withstand greater competition for resources. In this study, we test for relationships between woody plant functional traits and budburst phenology and phenological cues in deciduous species from across North America. We collected trait data across two latitudinal transects in western and eastern North America, and using the same individuals, performed controlled growth chamber experiments under varying environmental conditions. Combining these datasets, we tested whether gradients in budburst responses to temperature and daylength follow similar gradients in trait values. We found trait variation in height and the ratio of leaf carbon to nitrogen to explain the variation in phenological cues across species. But other key traits, such as leaf mass area, showed weak relationships. Furthermore, the relative responses in our eastern versus western forests differed considerably in the importance of certain traits to phenological responses. Our findings suggest that some traits covary with budburst phenology. But the differences we observed both across species and between our eastern and western transects highlight the importance of variation in functional traits in shaping community dynamics and site-level community assembly across North American forest communities.