Trees are perennial, woody plants with a single stem (trunk), normally greater than 13 to 16 ft. (4 to 5 m.) in
height. Under certain environmental conditions, some tree species may develop a multi-stemmed or short growth form of
less than 13 ft. (4 m.) in height. The following species have been reported to be invasive in natural areas in the
U.S. Species native to the U.S. are included when they are invasive in areas well outside their known natural ranges,
as a result of human activities. For more information on each species, including the listing sources, images, and
distribution maps, click on the species.