Highly competitive with native rangeland plants, it forms dense monocultures and increases fire hazards. English ivy, long a favorite in formal gardens, is extremely aggressive, killing native plants from trilliums to Douglas-firs. It is a particular problem in urban areas, where it was introduced to gardens and has since spread to parks and natural areas. Himalayan blackberry forms dense impenetrable thickets, generally in disturbed areas. Vigorous, erect canes can grow 20 to 30 feet in one season.
Scotch broom invades disturbed sites such as clearcuts, dredge spoils, and roadside clearings.
It produces prolific seed crops and propagates by popping and shooting seeds many feet. It spreads rapidly and out competes native plants. Other well-known invasive exotic plants include kudzu, Eurasian milfoil, and water hyacinth. Carp were first introduced to the United States in the 1870s by the secretary of the Smithsonian Institution. They were subsequently widely introduced in lakes and reservoirs, generally for the purpose of consuming oxygen-depleting algae.