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Important Notes and Citations

The U.S. Forest Service conducted the 2013-2027 National Insect and Disease Forest Risk Assessment to provide a nationwide summary of potential tree mortality caused by major forest pests. Results from this assessment have been summarized by various land-unit types, including by: National Forest, National Park, U.S. Fish and Wildlife Service units, Tribal lands, and state counties. Depending on local needs and assessments these data can be used to support:

  • Prevention and suppression activities for integrated pest management
  • Restoration efforts
  • Ecosystem resiliency management
  • Short and long term monitoring efforts
  • Fuels and fire management
  • Social, economic, and ecosystem services
  • Climate change research and management
  • Identification of potential wildlife habitat
  • Evaluation of the historic range of variability

The data presented in this website is not intended to dictate local management activities, nor does it suggest that tree mortality always has negative consequences. Management decisions are best made at the local level, based on the best available information.

This website is designed to raise awareness about forest health issues and provides common ground for consultation between resource managers and forest health specialists. Forest insect and disease summaries by National Forest, National Park, or other units can be used as announcements or bulletins that serve to advise and warn of potential hazards to trees within those units. Areas having the potential for forest insect and disease activity represent places where conditions are favorable to pest activity, even though their activity may not yet be occurring or imminent. These tree pests should be on your radar!

Source Data

Data in this website represent model output from the 2013-2027 National Insect and Disease Forest Risk Assessment (aka 2012 NIDRM).

Data herein also represent NIDRM's forest parameters data (including by-species basal area per acre distributions) used as NIDRM model inputs.

For details about how forest parameter data were derived and how NIDRM risk models were built, see:

Krist, Frank J., Jr.; Ellenwood, James R.; Woods, Meghan E.; McMahan, Andrew J.; Cowardin, John P.; Ryerson, Daniel E.; Sapio, Frank J.; Zweifler, Mark O.; Romero, Sheryl A. 2014. 2013-2027 National Insect and Disease Forest Risk Assessment. FHTET-14-01. Fort Collins, Colorado: U.S. Department of Agriculture, Forest Service, Forest Health Technology Enterprise Team.

Forest Parameter Information

NIDRM's basal area (BA) modeling was originally performed at (gridded) 30m resolution and was then subsequently upscaled to 240m resolution.

The BA modeling resulted in estimates of tree species BA density (square feet per acre) across the entire U.S. for hundreds of tree species.

The BA values reported herein are the result of geoprocessing and summarizing the gridded 240m BA estimates within each of the different land units.

All BA values represent live trees only, and represent estimates for trees greater than or equal to 1 inch diameter at breast height (DBH). Breast height is 4.5 feet above base of tree.

Species group BAs are derived by summing the BAs of the individual species composing the group.

"Treed" pixels are those have non-zero modeled BA.

For details about forest parameter modeling in Hawaii, which was performed differently than in the coterminous U.S. and AK, see the NIDRM document cited above.

The BA estimates represent conditions as of (approximately) 2012.

Areal Extent Information

National Park Service boundary datasets were provided by the Natural Resource Stewardship and Science, Biological Resource Management Division.

National Forest System administrative boundaries were derived from the federal lands layer in

U.S. Fish and Wildlife Service boundaries were derived from the “USFWS Cadastral Geodatabase” available from USFWS Geospatial Services.

The most recent officially endorsed Tribal lands boundaries dataset (AmericanIndianReservations_2007.shp) was provided by the Bureau of Indian Affairs.

County boundaries were derived from the “Two Million-Scale County Boundaries of the United States” layer from

All NIDRM risk modeling was performed at 240m pixel resolution (~14.23327 acres), except in Hawaii, where modeling was performed at 30m pixel resolution.

Agent information

NIDRM models estimate a potential 15 year mortality to individual tree species or species groups attributable to individual agents or (in a few cases) to agent groups.

NIDRM modeled mortality is expressed in terms of basal area, having units of square feet per acre.

Individual NIDRM models are specific for particular geographic areas, as defined by Bailey's ecoregions (Bailey, 1976).

There are 186 NIDRM models representing 43 agents acting upon 63 hosts or host groups.

Some of the NIDRM model results have been "collapsed" into agent groups for reporting herein. These include the agent groups dwarf mistletoes and Ips spp.


In the NIDRM, pixels are considered to be at risk if the modeled 15 year BA loss rate across all tree species and across all agents is greater than 25% of the total BA.

Unlike the rest of the United States, there was insufficient data to adequately model total BA in Hawaii. The 25% loss rate risk threshold for Hawaii is based on the average loss rates for its 4 modeled agents.


Bailey, R. G. 1976. Ecoregions of the United States (map). Ogden, Utah USDA Forest Service, Intermountain Region. 1:7,500,000.