In a nutshell
Most studies of phenology have focused on events that occur in spring at the beginning of the growing season. As a result, we know less about factors that influence when autumn events like leaf color and leaf fall occur. The timing of these events has important consequences for plant communities, wildlife species, and nutrient cycling.
To better understand what triggers leaves to change color and fall, a team of researchers used Nature’s Notebook observations from more than 100 woody plant species at sites across the country. They used newly developed models to show that weather plays an important role in determining when autumn events occur, but the effects were not the same everywhere. In the eastern U.S., warm summer temperatures delay when leaves begin to change color. In the western U.S., rainfall has more influence than summer temperatures. When lots of rain falls between January and March, leaves tend to change color and fall later than normal.
The results from this study can be used to help predict how woody plant communities will respond to climate change. Increasing temperatures may result in longer growing seasons, particularly in the eastern U.S. In contrast, drought conditions in the western U.S. may lead to earlier leaf fall and shorter growing seasons.
What is special about this study?
The researchers used novel modeling techniques to show that autumn phenology differs regionally and differs among plant species. Their analyses were only possible because Nature’s Notebook observers collect data throughout the year for large numbers of plants across a wide geographic region. The results showed that the effects of temperature and precipitation varied regionally, which allows researchers to make local predictions about autumn phenology.
What does this mean for YOU?
Results suggest that climate change is likely to alter the timing of autumn events and change the length of growing seasons. While these changes could be beneficial for some species, they could also have negative implications for plants that need a dormant period before initiating growth in spring. You can help researchers refine and expand on these analyses in the future by continuing to submit observations of autumn phenology for plants in your area to Nature’s Notebook.
Citation:
Li, X., A. Donnelly, A., and Y. Wang. 2026. Contrasting precipitation controls on autumn phenology across eastern and western U.S. Agricultural and Forest Meteorology 384:111190. https://doi.org/10.1016/j.agrformet.2026.111190