Elizabeth Wolkovich

Climate change is having a considerable impact on the timing of species life history events (phenology). Most species phenologies are advancing, while other species phenologies are either not changing or occurring later in the year. Phenological shifts can alter the environment under which species grow and potentially produce asynchrony in species interactions. Accurate predictions of phenological change are essential to understanding how climate change will impact species and community dynamics. But as of yet, we lack consistent knowledge of what causes the observed high species variability, both across the tree of life and at the community-level. In my thesis, I performed a meta-analysis in which I combined phenological time-series for over 1200 species with data on their life history traits, evolutionary history, and geography. My findings illustrate the importance of accounting for species evolutionary history, but contrast the results of previous studies, as I failed to find strong trophic-level differences or geographic trends. To better understand the community-level drivers of phenological variation, I performed a controlled environment experiment using spring budburst in North American woody plants as a case study. Again I found strong phylogenetic structuring of species budburst, but little variation in environmental cues across populations. Despite accounting for the effects of the three primary cues of budburst, I found a considerable amount of unexplained variation across species, which suggests additional traits or environmental cues contribute to species budburst timing. In my final chapter I identify traits that could be driving this pattern. Combining six trait measurements with my experiment results, I tested whether phenology correlated with gradients in other traits and the growth strategies they infer. Only a subset of traits correlated with photoperiod, and none with temperature, suggesting that gradients in phenology do not align well with our current understanding of trait variability. The results of my thesis illustrate the high species-level variation in phenologies in response to climate, as well as the relative importance of phylogenetic structuring of phenology in improving our understanding of the mechanisms driving phenological variation.

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