Plants That Won't Stay Put

Think of an ecosystem as a precision watch. The numerous levers, springs and cogs in the watch fit together as a harmonious, functioning whole. Introducing exotic species can be compared to opening the back of the watch and throwing in some additional parts. They may stay out of the way and have no effect. They might cause the watch to run fast or slow. Or, an extra part may fall into just the right spot to stop the watch completely. An example of a "stopped-watch" ecosystem might be a formerly diverse forest that has become completely covered by kudzu-an exotic vine -to the extent that only kudzu grows there.

When you look closely at a Missouri landscape you may find a great diversity of plants that coexist in apparent harmony. But in reality you are looking at a fierce competition. For thousands of years, plants native to Missouri have competed for available space, light, soil, water and nutrients. In the last few hundred years a host of exotic plants have arrived here from all over the world and tilted the balance of the struggle.

Some exotic plants, otherwise known as non-native or alien, were brought here intentionally. Others arrived by accident, perhaps as seeds hitchhiking on ships' cargo or in packing material. Many of these plants originated in Europe or Asia and were brought to North America during the earliest periods of exploration and settlement. Others continue to be introduced thanks to the expansion of global commerce.

Through millennia, our native plants have formed connections to many other elements of the landscape. A native plant may be tied to a particular insect that will collect and distribute its pollen to ensure seed production. Other insects may feed on the plant's foliage, stems, roots, flowers, or seeds, or they may drink the nectar it produces. Underground, the plant's roots may be connected to a specific fungus that improves the plant's access to nutrients in the soil. Other fungi, living in the plant's leaves, may harm the plant's health and keep the species from becoming more widespread.

Exotic plants, on the other hand, have been removed from their own native environments and transported to foreign regions that don't have the pests, diseases and competition from other species that kept them in check in their homelands.

Most non-native plants that were brought to North America have not spread aggressively. Tulips, originally from Asia, are an example. They stay where