Plant phenological responses to experimental warming-A synthesis

Although there is abundant evidence that plant phenology is shifting with climatic warming, the magnitude and direction of these shifts can depend on the environmental context, plant species, and even the specific phenophase of study. These disparities have resulted in difficulties predicting future phenological shifts, detecting phenological mismatches and identifying other ecological consequences. Experimental warming studies are uniquely poised to help us understand how climate warming will impact plant phenology, and meta-analyses allow us to expose broader trends from individual studies. Here, we review 70 studies comprised 1226 observations of plant phenology under experimental warming. We find that plants are advancing their early-season phenophases (bud break, leaf-out, and flowering) in response to warming while marginally delaying their late-season phenophases (leaf coloration, leaf fall, and senescence). We find consistency in the magnitude of phenological shifts across latitude, elevation, and habitat types, whereas the effect of warming on nonnative annual plants is two times larger than the effect of warming on native perennial plants. Encouragingly for researchers, plant phenological responses were generally consistent across a variety of experimental warming methods. However, we found numerous gaps in the experimental warming literature, limiting our ability to predict the effects of warming on phenological shifts. In particular, studies outside of temperate ecosystems in the Northern Hemisphere, or those that focused on late-season phenophases, annual plants, nonnative plants, or woody plants and grasses, were underrepresented in our data set. Future experimental warming studies could further refine our understanding of phenological responses to warming by setting up experiments outside of traditionally studied biogeographic zones and measuring multiple plant phenophases (especially late-season phenophases) across species of varying origin, growth form, and life cycle.

Automated summary

The review of 70 studies involving 1226 observations of plant phenology under experimental warming shows that early-season phenophases of plants are advancing in response to warming, while late-season phenophases are marginally delaying. The magnitude of phenological shifts shows consistency across latitude, elevation, and habitat types, with nonnative annual plants showing a larger response to warming compared to native perennial plants. Experimental warming methods generally yield consistent plant phenological responses, but there are gaps in the literature for non-temperate ecosystems, late-season phenophases, annual plants, nonnative plants, and woody plants and grasses. Further studies should focus on setting up experiments in different biogeographic zones and measuring multiple plant phenophases to improve predictions of warming effects on phenology.