News

Strolling down the Atlanta BeltLine this time of year, you might notice a lot of brown within the landscape: dead-looking flowers and grasses, crushed leaves under mostly leafless trees. This contrasts greatly with what you might expect to see in a city arboretum, and it might lead you to wonder whether it is simply a field of weeds left unmanaged. But there is a story here, and there is more happening than meets the eye. As with all other seasons, a meadow in winter holds the key to abundant life, and seen with discerning eyes, it can offer a world of beauty.

Dormant meadow

So what happens in the winter within the Atlanta BeltLine Arboretum? Here in the Piedmont, where we live in Atlanta, lawns and a few common species of evergreen ornamentals do not accurately illustrate the diverse plants and animals that would naturally reside here. While it is visually and mentally appealing to see all that green in a winter landscape, it doesn’t tell the true story of our land.

Yes, you can find evergreens here (think native hollies, Christmas ferns, and evergreen magnolias), but the Piedmont is mostly defined by deciduous forests that go largely dormant in the winter. The Piedmont also historically had pockets of meadow habitat in areas visited by regular fires, along waterways, and in areas heavily grazed by animals. Though these meadows have declined by 90%, they are still biodiversity hotspots. You’ll find this habitat growing along the Atlanta BeltLine Arboretum in the form of human-created meadows. Just as in the forest, herbaceous perennials that grow in meadows appear dead in the winter, but there is actually a lot going on if you know what to look for!

Song sparrow on cattail

When the tops of meadow plants die back in the winter, the roots extending deep underground are alive and well and will provide the plant with the fuel it needs to resprout next spring. If you look closely, you may see green leaves at the base of some dead-looking plants like bushy heath aster (Symphyotrichum ericoides) or goldenrod (Solidago sp.): these are called basal leaves and can last all winter until next year’s new growth. Native clumping grasses such as little bluestem (Schizachyrium scoparium) or switchgrass (Panicum virgatum) might be browning, but if you look more closely you will see that their seed heads can be quite beautiful. In fact, they provide a source of winter food for many different species of birds, including native sparrows, finches, and the vibrant cedar waxwing. This is why we leave them standing all winter.

So, in this winter landscape, are there any insects? While many insects are dormant in the winter, signs of them abound even now. Bumblebees can occasionally be seen clutching the stems of the last of the late wildflowers on sunny days. Moths might be found nestled beneath fallen leaves. Ants still come out on sunny days too and can be found marching up trees and standing stems.

Another fascinating phenomenon can be found on many of the abundant Canada goldenrods (Solidago canadensis) which in the summer have bright golden blooms. The tall stems (covered with dead brown leaves) are still standing now, and if you look closely you might find a stem with a protrusion shaped like a sphere.

Goldenrod gall in spring

Goldenrod gall in winter

This rounded growth is actually the nursery of an insect called the goldenrod gall fly, Eurosta solidaginis. This fly spends its whole life cycle on goldenrod. When a female is looking for a goldenrod to lay her eggs on, she can be quite picky. Some plants are more palatable than others to the goldenrod gall fly, and a female determines this by “tasting” different plants. Once she finds an acceptable plant in the springtime, she lays her eggs in the goldenrod stems.

When the larvae hatch within a few days, they immediately begin eating the plant. The larvae’s saliva contains a chemical that mimics the goldenrod’s own hormones, promoting its growth, and forming a gall within three weeks. This gall becomes nearly the size of a golf ball, has a corky exterior, and is filled with specialized tissue with the consistency of damp wood that the larvae consumes. Though dramatic in appearance, the gall does not harm the goldenrod’s growth, and it still blooms in the spring. That fall, the larva within chews a tunnel almost to the gall’s surface, leaving just a thin membrane between larva and the outside world: it is from this point that the larva will emerge the following spring.

Because it cannot chew its way out of the gall, the newly transformed fly inflates a balloon-like structure between its eyes which pops the thin membrane to the rest of the world. The adult fly that emerges is smaller than a housefly with mottled brown, nearly translucent wings, and will live just 10-14 days, during which time he or she will focus on mating and laying eggs. As clumsy fliers, they are mostly found walking up and down goldenrod stems in the spring. So be on the lookout for the galls sheltering the larvae the next time you take a stroll down the BeltLine.

So much life can be found within the Arboretum meadows all year round. What can you find in our winter landscape?

Written by Kelly Coles

Published January 16, 2020