An invasive plant is one that grows beyond its natural range and moves into an area, overwhelming the native plants and becoming the dominant species.
According to Executive Order 13112, signed on February 3, 1999 and establishing the National Invasive Species Council, an "invasive species" (including plants) is defined as an alien species whose introduction does or is likely to cause economic or environmental harm or harm to human health.
Most invasive plants were first introduced into North America on purpose. Usually the invasive nature of the plant was unknown before it was introduced, but without the diseases or pests that would have kept the plants in check where they naturally occurred, the plants were able to proliferate and become invasive.
Here in Bucks County, Pennsylvania, invasive species are spreading because of development and fragmentation of natural areas. Invasive plants seem to prefer areas where there has been soil disturbance. Depending on the species, invasives are easily spread by wind, animals, water or people.
To prevent the spread of invasive exotic plants: