Summer 2001

Invaders from Weedland

Ah! The beauty of wildflowers! Or are these weeds? To most people, the picture above is one of richness and beauty. An ecologist would agree. Yet the ecologist would see, technically speaking, weeds.

The white flowers with the yellow centers are ox-eye daisies — garden escapes from Europe that are among our commonest wildflowers. The yellow is moth mullein, and the brown-topped grass is meadow fescue. All three of these are alien weeds.

Ecologists define weeds somewhat differently than gardeners do. To the ecologist, a weed is a plant that heals disturbances. Something destroyed the original nature of the ecosystem here. Maybe a bulldozer, or a plow. There is healing in progress here. Beautiful healing.

Most weeds are wonderful plants. Some are native and some are alien. We hear a lot of talk these days about alien invasives. We'll get to them below. But most aliens are a valuable part of local ecosystems. An alien red clover can supply delicious nectar to the rare Aphrodite butterfly. More importantly, a turf of simple weeds — native or alien — is like a healthy scab that begins the healing of a wound. Weeds in nature go away gradually, once the disruption of the ecosystem has stopped.

Toward the bottom right in the top photo, you may be able to pick out the leaves of a dandelion. These leaves have the recurved "lions teeth" that gave the plant its name (the "dande" is from dens/dental meaning teeth). As in your yard, if you stopped mowing and left nature alone, the dandelions would go away in time. They thrive on mowing or trampling but can’t compete in a rich prairie or forest.

If the recovering area shown here were in a prairie preserve, these weeds would be part of the healing process that would tend eventually toward complete recolonization by the ancient plants that the bison and elk ate. (The leaves of arrowhead, visible in the water, show that some of those ancient native plants are reasserting themselves already.) If this were part of a well-managed forest, the ecosystem that would win out would feature trees. Classic weeds can be a healing step toward either forest or prairie.

But disaster lurks. Notice the blue and pink flower. It's crown vetch, an invasive. Invasive plants and animals, whether native or alien, are one of the major threats to healthy nature. To be sure, crown vetch may seem to behave like a weed after an ecosystem is damaged. But it doesn't yield to the diversity that makes for healthy ecosystems; in fact it invades and degrades healthy ecosystems.

Crown vetch can spread across prairie and eliminate most of the richness of life there. Invasives in both prairie and forest include native trees and shrubs. It’s not the alienness or nativity that makes the difference. It's whether the species is one of the "out of balance" or "aggressive" invasives that crowd out biodiversity and degrade the natural community.

Land managers are learning to control invasives in field and forest. With invasives in check, we can once again appreciate the beauty of simple weeds.

Words by Stephen Packard. Weed photo by Walt Anderson/Root Resources. Butterfly photo by Jan Kanter.

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