Why Phenology?

Why is Understanding Phenology Important?


Pine warbler at John Heinz National Wildlife Refuge
Photo: USFWS

Phenological observations have been used for centuries by farmers to maximize crop production, nature-lovers to anticipate optimal wildflower viewing conditions, and by almost all of us to prepare for seasonal allergies.

From a cultural viewpoint, we time festivals and events around specific phenological events. For example, a Cherry Blossom Festival happens during the first two weeks in April in Washington, D.C., whether or not there are cherry blossoms. The festival traditionally ends with a parade through blooming trees, but over the past few decades the cherry trees have been blooming earlier and now the parade happens after the peak bloom. The flowers bloom in response to warming temperatures, so if climate change is causing it to be warmer earlier in the year, the flowers will bloom earlier as well.

Having a parade for cherry blossoms while the blooms are fading is bad timing, but it is perhaps not quite as dire as some cases of bad timing that affect entire ecosystems. For example, in most ecosystems, there are insects and plants that need each other. Hungry insects searching for nectar from flowers inadvertently transport pollen from flower to flower. The pollen grains hitch a ride, often by sticking to an insect's legs. By distributing pollen, the insects, called pollinators, are fertilizing the flowers, allowing the plant to grow seeds and fruit.

But it takes time for insects to develop from egg to larva to adult, and the timing of their growth can't be sped up just because the flowers are blooming earlier. As the climate warms, plants may become out of sync with the insects that pollinate them. If an insect is still a larva when the flowers blossom, for example, it will not be able to fly from flower to flower to transport pollen. Without pollination, the flowers will not be fertilized and will not produce fruit.


Cotton mouse (Peromyscus gossipinus), found in the
southeastern United States
Photo: Wikipedia

Mammals in the ecosystem can be affected too. For example, consider mice. Some mice eat insects and seeds. If plants bloom too early for insects to pollinate them, then the seeds won't grow. And if the insects are too late to gather food from the flowers, they will not survive either. Without seeds or insects to eat, the mice may not survive. And animals that eat mice, like snakes and hawks, will also go hungry.

Changes in phenological events can also have a significant impact on how we humans live our lives and interact with our environment on a daily basis. For example, the timing of when plants flower and fruit can affect our food supply and therefore our health. Pollen allergies can also be exacerbated by changes in growing conditions. People who are allergic to plant pollen will experience reactions to the changes in flowering times and the lengthening of the growing season.

From historical records and observations, we know that phenological events can vary from year to year. Ecosystems can recover from variation between years, but when these changes happen consistently over many years, the timing of events such as flowering, leafing, insect emergence, and allergies can impact how plants, animals, and humans are able to thrive in their environments.