Assessing regional-scale patterns of insect and disease damage to forests

PARTNERS: North Carolina State University Department of Forestry and Environmental Resources; USDA Forest Service Forest Health Monitoring Program and Forest Health Protection

SUMMARY: Monitoring the occurrence of forest pest and pathogen outbreaks is important at regional scales because of the significant impact insects and diseases can have on forest health across landscapes. Every year, the Forest Health Protection (FHP) Program of the Forest Service and its partners in State agencies identify millions of hectares of damage caused by insects and diseases across forests of the United States, mostly through low-altitude aerial survey efforts. Analyzing this data allows for the identification of areas at greater risk of significant ecological and economic impacts and for the selection of locations for more intensive monitoring and analysis.

An Eastern Threat Center cooperator at North Carolina State University (NCSU) works annually with partners in FHP to summarize, by region, the area of U.S. forests affected by insects and diseases that cause forest mortality and defoliation, and to identify statistically significant geographic hot spots of insect and disease disturbance. Within the continental United States, the hot spot approach employs the Getis-Ord Gi* spatial clustering statistic of a nationwide lattice of hexagonal cells (ideal for use in spatial neighborhood analysis) to find areas with higher proportions of surveyed forest affected by mortality or defoliation than expected by chance. The proportion of surveyed forest affected by mortality and defoliation is summarized by ecoregion in Alaska and by island in Hawaii.

IDS_mortality_hotspots_2016_061818.pngHot spots of exposure to mortality-causing insects and diseases in 2016 for the 48 conterminous States. Values are Getis-Ord Gi* scores, with values greater than 2 representing significant clustering of high percentages of forest area exposed to mortality agents. (No areas of significant clustering of low percentages of exposure, < -2, were detected.) Click image to enlarge.



Percentage of surveyed forest in Alaska ecoregion sections exposed to defoliation-causing insects and diseases in 2016. Click image to enlarge.


This project is supported by Eastern Threat Center funding.

STATUS: Ongoing

PROGRESS: The quantification of large-scale patterns of forest mortality and defoliation, using Insect and Disease Survey data, has become a standard component within the annual Forest Health Monitoring national reports. Chapters presenting the results are included in the 2008-2018 editions. A paper published in the journal Landscape Ecology describes this approach in detail. An effort is also under way to analyze trends over time in insect- and disease-related forest mortality and defoliation. This research has been described in a number of other publications and presentations.


Forest Health Monitoring National Technical Reports

Forest Health Protection Insect and Disease Survey

Kevin Potter, NCSU Department of Forestry and Environmental Resources, or (919) 549-4071

Updated June 2018

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