Phenology Defined


Common lilac
Photo: Kirsten Meymaris

How does a bear know when it's time to hibernate? Why do April showers bring May flowers? Plants and animals don't have calendars or watches, but many of them take cues from the changing seasons. Changes in weather with the seasons, such as temperature and precipitation, signal many organisms to enter new phases of their lives. For example, buds form on plants as temperatures warm in the spring. As temperatures cool in the fall, deciduous trees and shrubs lose their leaves and become dormant. The study of the timing of these changes is called phenology.

Phenology is literally "the science of appearance." The word phenology comes from the Greek words "phaino" (to show or appear) and "logos" (to study). Scientists who study phenology – phenologists -- are interested in the timing of specific biological events (such as flowering, migration, and reproduction) in relation to changes in season and climate. Seasonal and climatic changes are some of the non-living or abiotic components of the environment that impact the living or biotic components. Seasonal changes can include variations in day length, temperature, and rain or snowfall. In short, phenologists attempt to learn more about the abiotic factors to which plants and animals respond.

Cherry Trees
Cherry Blossoms in full bloom, Washington, DC.
Photo: Wikipedia

Examples of springtime phenological events that interest scientists include flowering, leaf unfolding, insect emergence, and bird, fish, and mammal migration. Think about the changes where you live that tell you spring is almost here. In the Washington, D.C. area, cherry blossoms are a sure sign that spring is on its way. In many parts of the country, people look forward to hearing the songs of the first robins of the season. California poppies are an indicator of spring to many along the Pacific shores. In the Midwest, the greening up of fields and pastures is a signal that winter is almost over.

Because spring temperatures are slower to warm at higher latitudes than they are at lower latitudes, the timing of life cycle changes in living things differs from place to place. For example, a cherry tree might bloom in Atlanta two months before a similar tree blooms in Chicago because temperatures warm earlier in the year in Atlanta than they do in Chicago. While people often say that "spring comes earlier" in warmer climates because the temperature warms earlier in the year, the timing of seasons is actually determined by Earth's orbit not temperature. Spring officially starts in the Northern Hemisphere on the vernal equinox – about March 20 – no matter what the weather is like.

The arrival of spring gets a lot of attention in terms of phenological events, with flowers emerging from their winter slumber. However, equally important phenological events happen throughout the year. In the case of Project BudBurst, don't let our name fool you. We want to know when you first notice the signs of all seasonal change in plants, like when the leaves change color in the fall and when summer wildflowers wither and finish their life cycle. You can tell us about these changes by making observations and sharing them with us through our website. By joining Project BudBurst, you will be part of a community of thousands of people across the country that are furthering the understanding of plant phenology.