Outdoors

Invasive species threaten our area’s native plants, animals

The American bullfrog is just one example of an invasive species found in Washington.
The American bullfrog is just one example of an invasive species found in Washington. Spokesman-Review, file 2004

Plants and animals have habitats that they depend on — they use their environment for food, water, shelter and reproduction.

Just like plants and animals, humans have habitats too. Your room is your habitat, as is your house, your school, your grocery store and beyond.

But the natural world also is your habitat. You use the natural world for things like hiking, exploring and playing. But unlike the minimal impact that squirrels or bears usually have, humans have the power to change natural environments on a large scale. That means it is our job to take care of the natural world, to protect animals, plants, habitats and humans.

One way to practice good stewardship is by being aware of and getting rid of invasive plants and animals. An invasive species is one that has been introduced from elsewhere and flourishes in its new home, at the expense of the plants and animals that were there before. It takes up all the space, sunlight or food from other species. This upsets the balance of the ecosystem, or the relationships between plants, animals and their habitat.

Your backyard is one type of ecosystem. Try going outside and noticing what plants and animals you see and how they interact with each other. What kinds of animals do you see? What do the bugs eat? Where do they make their home? Which animals eat bugs? What are some differences between open grass and under a tree? Under a bush? Next to a fence?

Ecosystems are fragile because they have spent a long time adapting and changing so each animal has a specific job within the ecosystem. When an outside species does grow out of control, it can upset that fragile balance. Invasive species get out of control when they are particularly suited to an environment, but the ecosystem isn’t prepared for them. For example, normally, predators would exist to keep their population under control, but in the new environment, they are left unchecked.

Imagine your friend has mice in their house. They get cats to eat the mice. The mice will keep breeding, but the cats will keep their numbers down. Now imagine the mice were brought to a new house where there were no cats. With no cats to eat the mice, the mice have more and more babies until the house is overrun with mice. That is what happens when an invasive species goes to a new ecosystem where it has no natural predators or natural enemies. Not all foreign species are invasive; many houseplants, for example, are known as exotic because they come from somewhere else, but they do not grow out of control.

Here are some invasive species we have in Western Washington:

English ivy is on the official noxious weed list in the state. It was introduced from England as early as the 1700s and has since become widespread. Ivy has a tendency to suffocate all plant species where it grows, creating fields of just ivy, known as an “ivy desert.” You may have seen ivy covering the trunks of trees; after a while, this will actually kill the tree. The weight can take down young trees, and for older, stronger trees, the ivy takes all the water and nutrients from the tree.

Himalayan blackberry might produce a delicious berry, but similar to ivy, it can grow out of control and create “deserts” where no other plants can grow. Once the vines have created a “desert,” it can prevent new trees from growing because it blocks sunlight. And because the fruits are so delicious, birds and other animals eat the fruit and spread the seeds all over. Native to Western Europe, Himalayan blackberry has long, trailing canes with sharp spines that grow quickly and stay sharp long after the plant is dead. If you’re going to try pulling out Himalayan blackberry, make sure to pull the root out or the plant will just grow more canes the next year.

Scotch broom also was introduced from Europe as a decorative plant, but quickly grew out of control. You might have seen Scotch broom growing along the side of highways. It is a brushy plant with bright yellow flowers, and can form vast fields of yellow where nothing else grows. The seed pods are spring-loaded so that when they are ripe the pods explode, scattering seeds far and wide — and once they land, they can last in soil for more than 30 years, making it very difficult to prevent new growth. The plants are toxic to animals, and the pollen can cause severe allergies in humans. The best time to cut Scotch broom is when it is in bloom, before seed pods form. Cut the thick main stalk, not just the branches, so the plant dies completely.

The American bullfrog is native to the United States, but only the central and southern regions. It was introduced to the West in the early 1900s by accident, and the population soon began booming. You may have heard their call at night, a low, throaty honking sound. Like many frogs, the bullfrog is a cannibal, and other frogs are a favorite meal. Many of our endangered native frogs fall prey to this voracious predator. And, American bullfrogs are so large that native fish won’t even eat the tadpoles. Females lay up to 20,000 eggs, making the frogs very difficult to get rid of.

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