Purple Loosestrife

Non-native species are also referred to as introduced, exotic, or alien species. The National Park Service defines non-natives as species that occur in a given place as a result of direct, indirect, deliberate, or accidental actions by humans. Plant species that are brought into an area as food, fiber, or ornamental landscape plantings can "jump the fence" and become established in the wild. Likewise, non-native animal species can be introduced into an area deliberately, for agricultural use or fish stocking; or by "hitching a ride" on objects like boat hulls and outboard motors. Many species find their way to new locations in crop seed, soil, or nursery stock.

Although many non-native species have had a positive impact on our society, these species would not have evolved with the indigenous species and are therefore not a natural component of the ecological system. In extreme cases, invasive non-native species can displace indigenous species, thereby degrading the integrity and diversity of native communities. Non-native species can also become pests, such as gypsy moths, fire ants, zebra mussels, and feral hogs.

There are currently about 12 non-native plant species in Acadia National Park that are of high management concern. Garlic mustard, Japanese barberry, and purple loosestrife top the recent ranking of Acadia's invasive plants. Garlic mustard is an early spring flower that can replace native spring ephemeral wildflowers and dominate the understory of deciduous forests and woodlands. Japanese barberry has the ability to reside in a wide range of habitats including forest understories, wetlands and fields, and it too can outcompete native plants. Purple loosestrife, although beautiful, is a noxious weed, well known for its capacity to rapidly invade wetlands, replace native vegetation and dominate those habitats at the expense of turtles, birds and other animals.