About Invasive Plants

What’s the big deal about invasive plants?

A million trees, to start with! That is our estimate of how many trees are at risk in Fairfax/Falls Church from invasive vines such as English Ivy and Asian Wisteria that are strangling and smothering them. That number will only grow unless we take action!

Then there are numerous invasive trees, shrubs, grasses, and groundcovers that are displacing the native plants and preventing new trees from growing.

The most fundamental problem with invasive plants is that they turn our natural areas into starvation grounds for birds and other wildlife. This is because plant-eating insects such as caterpillars for the most part can only eat the plants with which they evolved. Without those insects, the entire food chain collapses. . For example, a single brood of chickadees requires 6,000 to 9,000 caterpillars to fledge. To support this high demand for insects, chickadees often nest near native plants, which host the largest populations of caterpillars.

What are “invasive” plants?

  • “Native” plants are the ones that evolved here. Example: Flowering Dogwood

  • “Non-native” plants are ones that evolved somewhere else. Example: Japanese Azalea

  • “Invasive” plants are non-native plants that are causing harm or have the potential to cause harm to a given ecosystem or to human health or to the economy. Example: Bradford Pear

Not all non-native plants are invasive, but all invasive plants (using the legal definition of that word) are non-native. 

Where did invasive plants come from?

The climates of China and Japan are very similar to the eastern United States, so many invasive species came from there. Some came from other parts of Asia or Europe, with very few from the other continents. Invasive species don’t have to originate in other countries: plants that are native in one part of the United States could become invasive here in time. 

How did invasive plants get here?

Many species were brought in for gardens (such as Butterfly Bush), or for eating (such as Beefsteak Plant), or to use in erosion control (such as Autumn Olive), or for animal forage (such as Johnson Grass). Others came in accidentally, such as Japanese Stiltgrass which was used as packing material.

Why are some plants invasive?

When a plant is moved out of its native ecosystem, it leaves behind its natural controls, such as the insects that feed upon it. If it happens to produce a lot of seeds or runners, those can go berserk in a new environment.

Many invasive plants have notably long bloom times, flowering and producing seed for many months. On top of that, many invasive plants green up earlier in the spring and lose their leaves later in the fall. When you see a lot of green in the woods in March, there is a good chance that you are looking at Multiflora Rose or other invasive plants. 

Higher levels of CO2 in the air stimulate the growth of many species, as do shorter winters.. The climate catastrophe is greatly favoring invasive species. Native plants time themselves using other cues besides temperature, but invasive plants are more flexible.

Deer prefer native plants, so when their numbers are too high, invasive plants have an advantage.

How do invasive plants spread?

The more people there are in an area, the worse the problem. Many invasive species thrive on soil disturbance. People track seeds into natural areas and inadvertently plant invasive plants in their gardens. Birds prefer the berries of native plants, which provide them the nutrients they need, but in our neighborhoods they are forced to eat the invasive ones as well, which they then carry to other areas. You may not notice a problem with Japanese Barberry in your yard, but those berries end up in the woods and cause severe problems. (What you do notice is common garden weeds, the majority of which are non-native.)

Where can I find a list of invasive plants?