Sustain Our Nation's Forests and Grasslands

Assessing the health of U.S. forests

American Pine
Research on the bishop pine (Pinus muricata) shows a convergence of multiple stressors, including invasive pathogens and changes in seasonal water availability. Photo courtesy of Christopher Lee, California Department of Forestry and Fire Protection.

WASHINGTON, D.C. – Forests are complex ecosystems that are constantly changing due to tree growth, changes in weather and climate, and disturbances from fire, pathogens, and other stressors. The USDA Forest Service Forest Health Monitoring program tracks these changes every year across the nation as part of a forest health check-up.

The 2018 Forest Health Monitoring report is the only national summary of forest health undertaken on an annual basis. It contains short- and long-term forest health assessments for the continental United States, Alaska, Hawaii, Puerto Rico and the U.S. Virgin Islands. The report is important because it provides a vehicle for presenting research results in a timely and client-oriented way.

It identifies ecological resources whose condition is deteriorating, potentially in subtle ways across large regions. This requires consistent, broad-scale, and long-term monitoring of forest health indicators and the participation of multiple federal, state, academic and private partners.

Some of the report’s key findings include:

  • In 2017, 63 different mortality-causing insects and diseases were detected on nearly 8.1 million acres across the lower 48 states. Fifty defoliation-causing insects and diseases were detected on close to 120 million acres. Emerald ash borer was the most commonly detected cause of tree mortality in the East, while a variety of bark beetle species – especially fir engraver, western pine beetle, spruce beetle and mountain pine beetle – were major causes of mortality in the West.
  • Much of the southwestern U.S. and portions of southern California were affected by extreme drought conditions in 2017. Parts of the central Midwest, the northern Great Plains and the Southeast experienced moderate to severe drought.
  • The number of satellite-detected forest fire occurrences in 2017 was the fifth highest since the beginning of data collection in 2001 and the highest since 2014. Areas in the Pacific Northwest, the northern Rocky Mountains and California had the highest density of forest fire occurrences.
  • Analysis of Forest Inventory and Analysis data revealed that tree mortality is low relative to growth in most of the central and eastern US, with areas of the highest mortality found in riparian forests of the Great Plains. In contrast, mortality exceeded growth throughout much of the forest of the Pacific Coast states, especially in southern California.
  • The report also presents results from three FHM-funded studies of declining forest health in areas of special concern. Those chapters focus on the decline of bishop pine in California’s northern coast, the infestation of the Hawaiian native naio tree by an invasive insect, and the impact of rising temperatures on Great Basin bristlecone pine forests in Nevada and Utah.
  • The U.S. is large, and its forests are quite different in different parts of the country. As a result, the threats that forests face also vary from place to place. Most of our forests face at least one threat, whether that’s fire or an invasive insect pest or competition from nonnative plants.

The 2019 edition of the report will be published next summer.