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published in the 2002 State of the Nation’s Ecosystems Report as well as the 2003 and 2005 Web-Only Updates have been superseded by the 2008 Report and thus should be used with caution.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.

View Data for Recent Trends View Data for Historic Wildfire Acreage

What Is This Indicator, and Why Is It Important? This indicator reports the acreage of forest affected each year by several important types of disturbance: forest fires, insects, and diseases of trees.

Fires, insects, and diseases are, for the most part, natural influences on forests. However, at times, such influences can exceed or otherwise differ from what might be considered "normal" levels of these disturbances. For example, fire suppression may foster the conditions necessary for catastrophic fires, and introduced pests like gypsy moths and Dutch elm disease can devastate large areas.

What Do the Data Show? Fewer acres have been burned by wildfire in recent decades than in the first half of the 20th century. Since 1980, between 2 million and 7 million acres burned per year, down from a high of 52 million acres in 1930; the decline is largely due to fire suppression policies and practices. Note that the data reported here describe all wildfires, including both forest fires and grassland/shrubland fires. Although nationwide data do not show an increase in recent decades, data (not shown here) from national forests, which are mostly in the West, do show a significant increase.

Insect damage varies dramatically from year to year. Five insect species together affected between 8 million and 46 million acres per year from 1979 to 2002. Many insect populations go through major cycles of year-to-year variation. For example, much of the variation over the past 20 years results from such cycles for gypsy moth and southern pine beetle.

In recent years, 42–44 million acres have been affected by two major diseases/parasites (fusiform rust and dwarf mistletoe).

Discussion It would be desirable to be able to report on acreage affected by forest fires (as distinct from other wildfires), on the acreage subject to different levels of fire intensity, and on the acreage of prescribed fire (fires that are intentionally set as a management tool). In addition, data on the acreage affected by other diseases is not available. Finally, some non-native insects, such as the hemlock woolly adelgid, which affects half of all eastern hemlock forests, may spread widely before it causes damage that is apparent from aerial surveys.

See also Fire Frequency .