Theresa Crimmins is the Assistant Director of the USA National Phenology Network (USA-NPN), an organization that brings together citizen scientists, government agencies, non-profit groups, educators and students of all ages to monitor the impacts of climate change on plants and animals in the United States.

Ready or Not, Here Comes Autumn

  • Sep 16, 2015

The calendar tells us that autumn in the northern hemisphere begins Sept. 23, but do the plants and animals in your area agree with this proclamation?

In temperate environments, the autumn season is charismatic, characterized by dramatic color changes in deciduous trees. Also, many migratory birds begin to depart for their wintering grounds to the south. Pumpkins and apples ripen, squirrels frantically collect acorns, mushrooms spread spores, and frogs and bats begin to seek shelter for their winter hibernation.

The changes that plants and animals undergo seasonally, like leaf color change, leaf drop, migration, and hibernation, are known as phenology, and a lot of people carefully track phenology, or when these events happen each year.

Fall colors in Virginia

Fall colors in Alexandria, Virginia.

One way many people track phenology is through a program called Nature’s Notebook, run by the USA National Phenology Network. Through this program, volunteers periodically report on what’s happening in their yards. Are the trees in flower? Have leaves changed color yet? Are birds nesting? It’s a great opportunity to become more in-tune with your immediate surroundings. To learn more, check out their web page on how to become an observer.

What’s been reported so far?

As of this writing, it seems that autumn is just starting to arrive for much of the country. Reports for leaf color change are just starting to trickle in, and few reports of birds migrating have been made. So far, these events don’t seem to be occurring remarkably early or late this year.

Why does the timing of these events vary from one year to the next? Many of these seasonal events in both plants and animals are closely linked to local conditions like temperature, moisture availability, and day length. As the days shorten and temperatures cool in the fall months, plants and animals are cued to undergo changes such as leaf color change and migration. For example, this August has been much warmer and drier in California than last August; accordingly, observers have been reporting pollen release in coyotebrush, a common shrub, much earlier this year. Likewise, this August has been much cooler than average in the central U.S. In response, leaf color change is being reported earlier for common deciduous trees, such as red maple and sugar maple, in this region.

As the season progresses and days shorten and temperatures drop, we’ll continue to see plants and animals respond. Explore the reports of plant and animal phenology directly using the USA National Phenology Network’s data visualization tool, or report what’s happening in your yard!