What is an Invasive Plant Species? (Explained)

Invasive species are plants, animals, insects, or pathogens that can cause significant ecological, societal or economic harm when introduced to a new environment where they are not native.

Invasive species introduction into new areas can be accidental (e.g. via ships, humans, or wind) or intentional (e.g. by humans).

Each year, non-native species cause over 100 billion dollars in damage to the US economy.

Invasive plant species are of particular concern, as they are the leading cause of native biodiversity loss around the world. The effects of invasive plant species are vast and they are a major threat to native plant species, wildlife, the agricultural industry, society, and the economy.

Continue reading to learn more about invasive plant species, their characteristics, how they spread, and their impact.

What are Invasive Plant Species?

Invasive plant species are non-native trees, shrubs, and herbaceous plants that have the potential to cause harm to the environment, society, economy, and human health. 

Common characteristics of invasive plant species include:

  • Non-native
  • Fast-growing
  • Rapid reproduction of seeds
  • High dispersal ability aided by the wind, birds, and humans (knowingly or unknowingly)
  • The ability to adapt to a wide range of conditions
  • Tolerance of a wide range of environmental conditions
  • The ability to thrive in disturbed soil
  • A lack of wildlife that consumes the plant species
  • Aggressive and smothering roots 

Top 5 Invasive Plant Species

1. Purple Loosestrife

Was introduced to the United States from Europe and temperate Asia in the early 1800s for ornamental and medicinal use. It has thick roots that can spread over extensive areas and can degrade habitats for many birds, insects, and other species. It is known to crowd out native plants.

2. Japanese Honeysuckle

Was introduced from Eastern Asia to Long Island, NY in 1806 for ornamental use and erosional control. They out-compete native honeysuckles and other native shrubs and plants. Japanese honeysuckle is also known to impact forest regeneration as it reduces the quality of wildlife habitat, particularly for forest-dependent birds.

3. Norway Maple

Was introduced from Europe by an explorer in 1756. They have very shallow roots and produce a great deal of shade, which makes it difficult for grass and other plant species to grow in the understory. Norway maples are also rapid seed producers and tolerant of many different environments.

4. English Ivy

Was introduced from Europe in the early 1700s when colonists imported the plant as an easy-to-grow evergreen groundcover. It is known to wrap around trees and branches, which prevent the leaves of a tree from accessing sunlight and moisture. It essentially causes trees to become undernourished while providing the perfect environment for insects and other pests.

5. Japanese Rose

Was introduced in Japan in 1866 as a rootstock for grafted ornamental rose cultivars. It restricts human, livestock, and wildlife movement and displaces native vegetation.

How are Invasive Plant Species Introduced?

There are several ways that invasive plant species can be introduced to a new environment. Introduction can be unintentional or deliberate.

The unintentional introduction of an invasive plant species is the result of an accidental act (e.g. using the same shovel or equipment in two unique ecosystems).

Whereas, the intentional introduction results from a deliberate act by humans (e.g. planting a seed that was taken from another ecosystem).

Some of the most common examples include:

  • Dispersal: This occurs when a plant species is moved from one environment to another. Humans are often responsible for this, whether it is intentional or unintentional.
  • Hitchhikers: Species become unintentionally transported by catching a ride in places like equipment, hiking boots, or other places.
  • Importation: This often occurs with the best intentions. For example, plants are imported for gardeners as ornamentals. However, they can become invasive if proper precautions are not taken, and they are planted in unintended areas.
  • Illegal Trade: The illegal smuggling of fruits, vegetables, and plant species across borders can introduce harmful new plant species, insects, and parasites. That’s why border patrol takes this issue very seriously!
  • Natural Dispersal: Some species can expand ranges naturally.

Stages of Invasion

There are usually three stages of invasion to a new ecosystem.

  1. Establishment
  2. Spread
  3. Impact 

What are the Impacts of Invasive Plant Species?

The US Government has estimated that nearly 25% of the 20,000 plant species native to North America are at risk of extinction because of invasive plant species and related habitat loss. Native species are kept in check by the natural balance of their ecosystem.

However, the same balance is not achieved when an invasive species is introduced. As a result, invasive species can affect the ecological balance of their new environment and lead to a wide range of impacts.

1. Impacts on Native Species

Invasive plant species compete with native species for moisture, sunlight, nutrients, and space.

Because of invasive plant species’ ability to adapt and thrive in new environments, they displace and alter the environment of native plant species. This can lead to degraded wildlife habitats, reduced water quality, and even increased soil erosion.

Since many invasive species are not consumed by wildlife, it also increases the pressure on native plants for grazing.

Common Impacts of Invasive Plant Species on Native Plant Species

  • Smothering
  • Growing invasively
  • Blocking shade
  • Spreading aggressively
  • Aggressive roots systems that choke other plants
  • Preventing native plants from growing
  • Taking all the nutrients

2. Impacts on Ecosystems

Invasive plant species can harm how ecosystems function, how native plants grow, and the health and abundance of native wildlife.

They are also capable of causing native plants and animals to become engaged or extinct, which affects biodiversity and forces native organisms to fight amongst each other for limited resources.

Because of invasive plant species’ aggressive nature, one species can quickly replace a diverse ecosystem with a monoculture of just that species.

3. Impacts on Wildlife

The spread and establishment of invasive plant species can completely alter and degrade wildlife habitats. In addition, wildlife may eat invasive plant species that do not provide any food value to them.

Alternatively, wildlife may not graze on invasive species, which can create food shortages as native plants become limited. This can alter the abundance and diversity of wildlife species that are part of that ecosystem because their diet may be affected.

4. Impacts on Agriculture

The agriculture industry is affected by invasive species because of their ability to spread quickly and out-compete crop and forest plants. Invasive plant species can also deteriorate the soil quality, which further affects native plants and crops.

Invasive plant species can act as new or additional hosts for crop diseases and crop pests, which can cause a reduction in crop yields or increase the need for pesticides.

Once an invasive plant species have taken hold in a new environment, it is very challenging, time-consuming, and costly to remove them. Ultimately, invasive plant species can directly lead to poor quality agricultural lands, increased pests, and decreased yield.

5. Impacts on Society

Invasive plant species can impact recreational opportunities, compromise outdoor experiences and lead to health impacts. Invasive species can affect human health by introducing new diseases and harboring an environment for pests.

Invasive species can also increase the risk of wildfires. They often increase the frequency of fires because they create an abnormal amount of buildup on the forest floor that provides continuous fuels that are easier to ignite.

6. Impacts on the Economy

Invasive species often cause indirect economic impacts and indirect economic impacts.

Direct economic impacts include management costs, research and monitoring programs, reduced crop yield, lost jobs, damage to infrastructure, and effects on global trade.

Indirect economic impacts are often challenging to quantify but include loss of ecosystem services, reduced biodiversity, effects on tourism and recreation, and reduced property values.

How Can You Avoid Spreading Invasive Plant Species

The best way to stop the spread of invasive plant species is to prevent them from being introduced in the first place. While that is not always possible, there are a few things you can do to help stop the spread:

  1. When traveling, do not pick flowers, weeds, or plants to take home from you
  2. Verify plants you are buying for your yard and garden are not invasive
  3. Drive on established roads and trails
  4. Do not pick and transport wildflowers you can’t identify
  5. Clean your boots before you hike in a new area
  6. Don’t move firewood to a new area

Invasive species are named because of their aggressive colonization of new spaces. They can crowd out and kill the important tree and plant species that provide shade, carbon storage, and habitat for native wildlife.

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