To those that don't know, invasive plant species can be attractive, fragrant, and even welcomed additions to gardens and landscaping.
And, actually, many invasive plants started in people’s gardens.
They got introduced to an area from different countries. Since they lacked natural predators, they were able to thrive. And then they started taking over…
Learn more about invasive plant species, why they are so dangerous, and how we can help manage them in our parks and green spaces.
What Are Invasive Plant Species?
Invasive species are non-native plants introduced to an area. Their introduction could be intentional--like adding the plants to a garden--or more indirect--like birds eating berries and then spreading the seeds after digesting them.
Since they don’t have natural predators to keep their population in balance, the plant species take over areas.
To be considered invasive, their establishment is likely to cause environmental or economic harm--and could even be dangerous. Chinese Wisteria (Wisteria sinensis), for instance, could cause severe discomfort if ingested, like burning mouth, vomiting, nausea, and diarrhea.
Many invasive species have characteristics that allow them to establish themselves quickly. For example, many invasive plants thrive in disturbed areas where other plants have difficulty surviving.
They often produce many seeds distributed by the wind, birds, other animals, and humans. For example, one plant of the Purple Loosestrife (Lythrum salicaria) can produce up to 2 million seeds a year that the wind disperses. Another invasive plant, the Japanese Barberry (Berberis thunbergii), has seeds that birds easily spread.
In addition, some invasive plant species have aggressive root systems, like the Japanese Knotweed (Fallopia japonica). They could spread long and dense root systems that smother out native vegetation. And it’s not just underground. The vigorous vine Kudzu (Pueraria montana var. lobata) wraps around plants and trees to smother them.
Why Are They Such a Problem?
Invasive plants do more than just take over a section of land. They harm the environment, human health, and the economy. It’s estimated invasive species, directly and indirectly, cost the United States over $100 billion per year.
Invasive plant species crowd out and destroy native plants. With fewer native species, the area’s ecosystem gets thrown off. The area becomes a monoculture, reducing the quality and quantity of fish and wildlife habitat. Large areas of invasive species may prevent trees from becoming established, reducing the amount of tree cover.
According to the United States Department of Agriculture, invasive species have contributed to the decline of 42% of U.S. endangered and threatened species and are the leading cause of 18% of the endangered or threatened species.
Invasives also impact the quality of our ground cover. Plants that act as ground cover often have a shallow root structure. During heavy rains and flooding events, areas with less root structure diversity are more prone to erosion that releases sediment into water sources.
Researchers are currently doing experimental studies about how climate change will affect invasive plant populations. The changing temperature, precipitation, disturbances caused by severe weather, and elevated CO2 levels may make conditions even more favorable for invasive species.
Common Invasive Plant Species
In addition to the species mentioned above, here are some other common invasive plant species found throughout the United States:
- Japanese Honeysuckle (Lonicera japonica)
- Garlic Mustard (Alliaria petiolata)
- Cheatgrass (Bromus tectorum)
- Japanese Barberry (Berberis thunbergia)
- Winter Creeper (Euonymus fortunei)
- Russian Knapweed (Acroptilon repens)
- Hydrilla (Hydrilla verticillata)
- Running Bamboos (Phyllostachys aurea)
- Norway Maple (Acer platanoides)
- Reed Canary Grass (Phalaris arundinacea)
Many of these plant species are native to Europe or Asia.
Managing Lands With Invasive Plants
Invasive species are notoriously difficult to get rid of once established. The following methods provide the best chance to recover land disrupted by these plants.
Prevention is the most economical and safest way to manage invasive species. Staff should be aware of any established or encroaching invasive species in the area. Conduct regular inspections, especially in disturbed areas, with staff trained to identify plants that don’t belong.
When possible, protect healthy native habitats to prevent disturbances and the potential for infestation.
Use native plants for gardens, landscapes, and other green areas whenever possible.
Educating the community about the best practices to prevent non-native plants from taking over can also help the community take proactive measures to protect public lands.
The window of opportunity for early detection and rapid response is very small for many invasive plants. If there are emerging invasive species in your area, then it’s essential to inspect your natural areas for any emerging plants. Pay special attention to disturbed areas like roads, paths, natural area borders, and in heavily used green areas.
Early detection and rapid response using one or more control methods saves land, time, and resources compared to eradicating a widespread infestation.
Here are some standard methods used to eradicate or manage invasive plants.
If your team notices the emergence of an invasive species early enough, they may be able to address the issue by physical means.
Physical methods include:
The team must remove the entire plant when using manual methods to avoid resprouts.
Mechanical methods are similar to manual removal--just with a little more horsepower. Techniques can include mowing, tilling, girdling, or creating barriers.
Mechanical methods cause disturbances at a site making it more vulnerable. Occasionally, herbicides get applied to prevent rapid regrowth after mowing or tilling an area.
Herbicides provide an effective and resource-efficient means to manage invasive species. Many common invasive plants can be killed with one of two herbicides:
- Glyphosate (Roundup/Rodeo)--a non-selective herbicide that kills everything it contacts.
- Triclopyr (Brush-BGone/Garlon)--a selective herbicide that does not harm grass and grass-like flowering plants such as lilies or orchids.
State-issued pesticide applicator licenses may be required when applying these chemicals. Also, special formulas may be necessary when used in wetland zones.
Biological controls use insect predators or plant diseases to help combat the targeted species. Usually, the biological controls come from the non-native species’ home area.
Biocontrol can be complicated and have other environmental implications, so it’s best to research methods that have minimal impact on non-target species and the local ecosystem.
An Integrated Approach
Integrated pest management (IPM) is a process used to solve invasive species problems while minimizing risk to the environment and people. IPM uses research and science-based decision-making to merge tools and strategies to identify and manage pests.
IPM uses a combination of control methods--along with prevention and early detection practices--based on the type of invasive plants involved, the natural ecosystem, and the most effective practices that require the least resources.
Invasive plant species have already caused a great deal of environmental and economic damage to the country. Sadly, the threat doesn’t show any sign of slowing.
As parks professionals, our best line of defense is prevention and early detection. Creating best practices for preventing the emergence and spread of invasive plants can protect the native habitat and save time, money, and resources.
Be sure everyone on the team remains on the same page. Conduct routine in-services. Train someone on each crew to identify invasive plants. Maintain records of inspections, sightings of invasive plants, and the action taken to eradicate or manage the species.
Restoring native habitats can be one of our greatest gifts to future generations.