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 because they cause native biodiversity loss worldwide. Their effects are vast, and they are a significant threat to native plant species, wildlife, the agricultural industry, society, and the economy.

Please 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

Purple Loosestrife

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

Japanese Honeysuckle

Japanese honeysuckle was introduced from Eastern Asia to Long Island, NY, in 1806 for ornamental use and erosion control. It outcompetes native honeysuckles and other native shrubs and plants. Japanese honeysuckle is also known to impact forest regeneration, reducing the quality of wildlife habitat, particularly for forest-dependent birds.

Norway Maple

It was introduced in 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.

English Ivy

It was introduced in 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 prevents the leaves of a tree from accessing sunlight and moisture. It causes trees to become undernourished while providing the perfect environment for insects and other pests.

Japanese Rose

It 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 results from an accidental act (e.g., using the same shovel or equipment in two unique ecosystems).

Meanwhile, intentional introduction results from deliberate acts by humans (e.g., planting a seed from another ecosystem).

Some of the most common examples include:

  • Dispersal: Occurs when a plant species is moved from one environment to another. Humans are often responsible for this, whether intentionally or unintentionally.
  • Hitchhikers: Species are unintentionally transported by catching a ride in equipment, hiking boots, or other places.
  • Importation: This often occurs with the best intentions. For example, plants are imported for gardeners as ornamentals. However, if proper precautions are not taken and they are planted in unintended areas, they can become invasive.
  • 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 the invasion of 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 invasive species are 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 invasive plant species can adapt and thrive in new environments, they displace and alternative plant species’ environments. 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 root 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 invasive plant species are aggressive, 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 food value.

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 in that ecosystem because their diet may be affected.

4. Impacts on Agriculture

Invasive species affect the agriculture industry because they can spread quickly and outcompete crops and forest plants. They can also deteriorate soil quality, affecting native plants and crops.

Invasive plant species can act as new or additional hosts for crop diseases and pests, reducing crop yields or increasing the need for pesticides.

Once invasive plant species have taken hold in a new environment, removing them is challenging, time-consuming, and costly. Ultimately, invasive plant species can 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 harm health. 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 raise the frequency of fires by creating an abnormal buildup on the forest floor, providing 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 that the 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 they aggressively colonize new spaces. They can crowd out and kill important tree and plant species that provide shade, carbon storage, and habitat for native wildlife.

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