Phenology Phases in Full Force

May 19, 2022

Spring in the garden means a bustle of emergence and departure, a flurry of wardrobe changes, peeking and peaking, buzzing and alighting, bursting and retreating. Here at Southern Highlands Reserve, we’ve been recording the timing of these occurrences since 2008. Three times a week in the spring, staff and volunteers track the phenology phases, or life cycle stages, of 31 plant species including Fraser magnolia, witch hazel, blackberry bush, red maple, northern red oak and American chestnut.

Nature writers have been recording these events informally for centuries. For years in the mid-1800s, Henry David Thoreau took daily four-hour walks around Walden Pond and Concord, Massachusetts, and meticulously documented the leaf-out times of 43 plant species. A few years ago, researchers at Boston University were able to use these unpublished field notes to determine a significant shift in the timing of leaf emergence. In the 1850s, the mean date was May 8; 160 years later, it’s now April 20.

Phenology — the study of the timing of seasonal life cycle events — is one way to monitor the effects of climate circumstances like drought and rising temperatures. At SHR, we note phases such as flower bud swell, leaf bud swell, flower bud break, leaf bud break, leaves forming, leaves fully formed. In the fall, we’ll track the changing colors of leaves and when they drop. Over time, compilation of these dates creates patterns researchers can use to determine how plant behavior is changing.

The timing of these spring occurrences has a ripple effect on the success of pollination as well as on the life cycles of insects and birds. Even a short discrepancy in timing from year to year can mean the difference between thriving and a struggle for survival. Sometimes plants emerge too early and then pay the price of a late frost, which means less sustenance for birds and insects. Sometimes plants flower too soon, before bees and butterflies are active, and so miss out on pollination.

Elevation plays a role in timing as well, and as a high elevation garden, we’re able to provide data not readily available elsewhere. On Toxaway Mountain we are the “canary in the coal mine” for high elevation forests, providing evidence of long-term effects of climate change. These ecosystems have survived for eons as islands in the sky and are a result of the last Ice Age forcing species down the spine of the Appalachian Mountains. If changes in timing and survival are taking place here, they will soon occur elsewhere.

“It’s important to let researchers know what the climate is here, how many heating degree days we have,” says Director of Horticulture Eric Kimbrel. “It’s cumulative. As the days get warmer, plants and insects all react, and as it gets colder, the same thing happens. In the fall, actions are also dependent on the amount of daylight. When the days are getting shorter, the plants realize it and begin to go to sleep.”

At SHR, we train volunteers to be citizen scientists recording the progress of the seasons on the mountain. The accuracy and depth of our records is due to the dedication of our volunteers canvassing the garden each week to note these changes. It requires patience and a keen eye, and we are so thankful for our volunteers who help make all of this possible.

Anyone can get involved in tracking phenology phases thanks to the USA National Phenology Network, a partnership of volunteer observers, government agencies, nonprofits and educators. The organization runs a project called Nature’s Notebook, which enlists volunteers to track the weekly phenology phases of the plants and animals in their own backyards through an app.

To learn more, visit the USA-NPN website at