Note that the data published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution. For the most recent data, purchase the 2008 Report from Island Press.

What Is This Indicator, and Why Is It Important? This indicator describes the degree to which non-native plants are found in U.S. forests. It will report the percentage of the total area covered by overstory (large trees that form the canopy) and understory (shrubs, ground plants, and smaller trees) that is made up of non-native plants.

Species are generally considered to be non-native if their natural range does not include North America, although there is growing recognition that species that are native to one part of the United States may cause problems if they spread to other areas. Non-native species may spread aggressively and crowd out species that are native to a region; they may also alter essential habitat of native species, by shading native plants or by consuming large quantities of water, for example.

Well-known non-native species in the East include kudzu, melaleuca, and ailanthus, while western species include eucalyptus and Russian olive. Some non-native plants were introduced accidentally; others were originally planted for landscaping (e.g., Norway maple, multiflora rose) or for purposes such as erosion control (Russian olive). In general, forests with greater coverage by non-native species are subject to higher levels of ecological disruption, which may in turn have economic consequences.

Why Can't This Entire Indicator Be Reported at This Time? The USDA Forest Service Forest Inventory and Analysis (FIA) program is developing and testing protocols for reporting non-native plant cover. Data from this program will be included in future reports. For other non-native species indicators, see Coasts and Oceans, Farmlands, Fresh Waters, and Grasslands and Shrublands.