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Invasive Tree Species: How Invasive Trees and Plant Species Threaten Native Forests

When you think of invaders, you probably think of big armies that flood into a place and frighten and even harm everyone that already lives there. But did you know that some of the pretty trees and flowers that you see in people’s gardens or even on the side of the road are invaders that are harming the naturally occurring plants and animals that had been there previously? These invaders are non-native plants, and while they can be beautiful to look at, they can be dangerous to wildlife and – over time – humans.

There are numerous names for non-native plant species, including non-indigenous, exotic, and – when they become environmentally troublesome – invasive. While many non-native tree species might have been brought over to different habitats for ornamental (to make something pretty) or economic (to make money) purposes, their long-term effects tend to be devastating to the original forest, reducing environmental diversity and threatening native trees and plants.

When you look at certain invasive tree species, it’s easy to see why they became popular with gardeners and homeowners. Many of them are quite beautiful, thick with bright and colorful flowers and velvety leaves; they can make properties appear lush and well-maintained. However, their seeds can spread easily into surrounding regions, and they can cause considerable damage to native forests when allowed to multiply.

Approximately 250 tree species cause significant harm when they invade non-native ecosystems. Although 250 is considered a small number on the scale of total tree species, their ability to grow aggressively in a wide variety of climates and conditions, reproduce at a high rate of speed, and survive even harsh environmental circumstances make them highly difficult to manage.

The following non-native tree species can be a threat to their non-native ecosystem, and even a threat to human health if allowed to proliferate.

  • White or Silver Poplar
  • Chinaberry
  • Chinese Tallow
  • Chinese Sumac
  • Black Locust
  • Tree-of-Heaven
  • Princess Tree
  • Mimosa

In the Southern United States, forests are highly diverse, providing essential resources for native wildlife, as well as the raw materials for numerous consumer products. Invasive tree and plant species alter the chemistry of the native soil, reduce the diversity of the existing flora and fauna, impede native species regeneration, endanger native seedlings, and certain invasive species can even increase the risk of wildfires. Here is how invasive species affect the health and biodiversity of native forests.

Limit native forest productivity. Invasive species are like little thieves – they steal the nutrients other plants need to survive. The competition of invasive plant species – not limited to trees, but also including vines, grasses, shrubs, and herbs – can spread disease and raise mortality rates of native seedlings, preventing forest regeneration. Certain plants, such as the Chinese Wisteria vine, release chemicals that prevent other plant species’ reproduction.

Reduce wildlife populations. You know how when you’re in a library everyone is quiet and focused, but when you’re in a park or at the beach, everyone is playing and having fun? Different environments influence our behaviors, and invasive plants can change environments so much that the animals change their behavior, too. The invasive bush honeysuckle shrub, for example, attracts bird species for nesting due to the strength of their branches. However, because the shrub leaves are naturally thin, predators that wouldn’t normally be a threat can easily spot nests and attack the birds. Also, invasive trees and plants can inhibit the growth and productivity of native fruit-bearing trees and plants, effectively removing important food sources for native wildlife, causing them to migrate from their native environments.

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Threaten biodiversity. Healthy forests have lots of different plants and animals, but when an invasive species arrive, it can destroy those different plants and take over space completely. Invasive trees and plants can quickly displace native species by crowding out vegetation, altering the soil pH, and casting shade on forest understory (plants that grow on the forest floor alongside and underneath trees). Invasive trees and plants dramatically influence the creation of native vegetation, which results in a reduction of native insect and animal populations. This puts rare and endangered species at an especially high risk of extinction.

How to Manage Invasive Trees

Fortunately, precautions can be taken to limit the spread of invasive trees and plants. Here are a few strategies that may help preserve and regenerate native forests.

  • Recognize threatening invasive species in your community. Learn which garden trees and plants are invasive and how you can accurately identify them. If you see outcroppings of invasive trees or plants in your region, you can report them to the local conservation agency.
  • Limit the spread of invasive plants. Invasive trees and plants spread when seeds are carried from one region to another. If you go hiking, for example, and walk through an invasive weed species or near an invasive tree species that drop light seeds, you could carry those seeds on your shoes and spread them wherever you walk. Try to be conscious of the possibility of transmitting invasive plant seeds whenever you go in or around a native forest.
  • Plant native species in your garden. If you have an interest in gardening, make sure you plant only native trees and shrubs. By strengthening the native plant and tree population, you can help limit the proliferation of invasive species. Ask your local garden outlet which species are native to your region.

Forest Founders is committed to regenerating native forests all over the world. For more information about how you can help protect our forests, please visit Forest Founders information page.