Invasive plants can dominate native plant communities by forming monocultures that use the resources (e.g. nutrients, light, water) native plants need to grow. Kudzu (Pueraria montana) is a vine that grows throughout most of the southeastern United States and in some northern states.

Kudzu grows rapidly and can smother native plants, kill trees by girdling, and uproot trees by the weight of its vines (1). When kudzu grows very few other plants are able to survive, substantially decreasing native biodiversity.

European cheatgrass (Bromus tectorum) has spread throughout the sagebrush rangelands of the Great Basin in Idaho and Utah, predisposing the invaded habitats to fire. Some research shows that before cheatgrass invasion fires occurred once every 60 to 110 years, but now fires are more frequent, burning every 3 to 5 years (2).

Smooth cordgrass (Spartina alterniflora) was transported from the East Coast to West Coast, where it hybridizes with native California cordgrass (Spartina foliosa) (3).

Spreading populations of hybrid plants could result in loss of genetic material of native California cordgrass and lead to local extinction (4). Additionally, the invading hybrid and nonnative species create cordgrass “meadows” in naturally open mudflats. This modification of estuary ecosystems has far-reaching impacts on native species and on people (5).

At Lacreek National Wildlife Refuge in South Dakota, Canada thistle (Cirsium arvense) has expanded vastly in the last 10 years, crowding out native grass and forbs on the refuge. Neighboring cattle that normally eat the grasses won’t eat Canada thistle (6).

About 42% of federally threatened and endangered species are at risk primarily because of invasive species (7).

On the Upper Mississippi River National Wildlife and Fish Refuge purple loosestrife (Lythrum salicaria) crowds out native plants. Purple loosestrife may be the most ubiquitous invasive species in the United States; it has invaded about 400,000 acres of federal land, including wetlands, marshes, pastures and riparian meadows (8).

Purple loosestrife confines native wetland plants, including swamp rose mallow and some federally endangered orchids, to small areas. It also reduces habitat for waterfowl, which impacts declining species such as the bog turtle, black tern and canvasback duck (8).

Recreational activities such as swimming, boating and fishing can be impacted by invasive aquatic plants such as Eurasian watermilfoil (Myriophyllum spicatum). As Eurasian watermilfoil grows up from the bottom of lakes and rivers, it creates expansive mats on the water’s surface with dense tangles of stems below. As a result, recreationists are unable to use these areas and the health of the aquatic ecosystem declines (9).

Invasive plant infestations can also reduce the economic benefits of recreation-based activities to communities (10).

Environmental damage caused by invasive species such as melaleuca, combined with the cost of controlling them, adds up to almost $120 billion per year (2).