In a nutshell
There have been many efforts over the years to predict when plants will flower because the timing of these events has important consequences for plant and insect communities and human activities like agriculture and tourism. Eastern redbuds (Cercus canadensis) are one of the earliest flowering trees in North America. In the eastern U.S., the appearance of redbud flowers is one of the clearest signs that spring has begun. However, the timing of this event varies regionally and varies from one spring to the next, making it difficult to predict when trees in a particular location will flower each year.
To identify the conditions that trigger eastern redbud trees to flower, researchers used Nature’s Notebook observations from 152 sites across the species’ range. They developed a new approach that combined traditional models that account for temperature and daylength with a machine learning model. Researchers validated their results using historical data from herbarium records and recent observations submitted to iNaturalist.
The researchers found that both temperatures and daylength play a role in determining when trees flower, but the effects of temperature were not the same everywhere. Compared to trees in the southern U.S., trees in northern regions require extensive cold periods in winter but need less warmth in the spring to begin flowering. The results allowed researchers to predict within one week when Nature’s Notebook observers were likely to first observe open flowers on their local trees.
What is special about this study?
With their novel modeling approach, the researchers were able to accurately predict when redbud trees will flower each year. Researchers capitalized on the vast amount of information Nature’s Notebook observers have collected on eastern redbud trees, particularly since the Redbud Phenology Project campaign started in 2021. This study highlights the value of Nature’s Notebook campaigns, which can increase awareness and data collection efforts for high priority species.
What does this mean for YOU?
Results from this study underscore the important role that temperature plays in determining when plants flower. Warming temperatures will likely cause redbud trees in the southern U.S. to flower earlier in the spring. While this could benefit early-season pollinators, it could also have a negative impact if flowers open before a late spring freeze. You can help researchers refine models of flowering in redbuds and other plants by expanding the maps and submitting observations of plants in your local area to Nature’s Notebook.
Citation:
Mohammad, T., R. P. Guralnick, J. A. Santiago-Blay, and T. M. Crimmins. 2026. Hybrid machine learning approaches outperform mechanistic models of bloom timing in Eastern Redbud, Cercis canadensis. International Journal of Biometeorology 70:154. https://doi.org/10.1007/s00484-026-03197-2