Denser forests across the USA experience more damage from insects and pathogens

Area of Science:

• Forest Ecology
• Forest Pathology
• Forest Entomology
• Remote Sensing

Background:

• Increasing forest density across the United States raises concerns about resource competition and vulnerability to disturbances.
• Forest density metrics, such as total tree basal area (TBA), are crucial for assessing forest health and susceptibility to damage.
• Previous research suggests a link between forest structure and susceptibility to insect and pathogen outbreaks.

Purpose of the Study:

• To investigate the relationship between total tree basal area (TBA) and forest damage caused by insects and pathogens in the conterminous United States.
• To determine if TBA can serve as a regional-scale indicator of forest health and vulnerability.
• To identify areas requiring more detailed forest condition analysis based on TBA.

Main Methods:

• A raster map of total tree basal area (TBA) for the conterminous U.S. was created.
• Annual survey maps of forest damage (2000-2019) attributed to insects and pathogens were utilized.
• Median TBA was compared between damaged and undamaged forest areas across four distinct U.S. regions.

Main Results:

• Median TBA was significantly higher in forest areas experiencing defoliation or mortality from insects and pathogens compared to undamaged areas.
• This pattern held true across all four analyzed regions, indicating a consistent relationship.
• The findings suggest a strong correlation between increased basal area and heightened forest damage.

Conclusions:

• Total tree basal area (TBA) is a valuable regional-scale indicator of forest health.
• Higher TBA values can identify forests potentially more vulnerable to insect and pathogen disturbances.
• TBA can serve as an effective initial filter for prioritizing areas for more in-depth forest health assessments.