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

Abstract

Forests across much of the United States are becoming denser. Trees growing in denser stands experience more competition for essential resources, which can make them more vulnerable to disturbances. Forest density can be expressed in terms of basal area, a metric that has been used to assess vulnerability of some forests to damage by certain insects or pathogens. A raster map of total tree basal area (TBA) for the conterminous United States was compared with annual (2000–2019) survey maps of forest damage due to insects and pathogens. Across each of four regions, median TBA was significantly higher within forest areas defoliated or killed by insects or pathogens than in areas without recorded damage. Therefore, TBA may serve as a regional-scale indicator of forest health and a first filter for identifying areas that merit finer-scale analysis of forest conditions.

Silvicultural treatments improve pest and disease conditions of white pine (Pinus strobus) residual trees and regeneration

“…Host density may facilitate or slow down the development of disease epidemics or pest outbreaks (Asaro et al, 2023) and understanding effects of host density is therefore critical to management of resilient forests. Shelterwoods and low-density thinnings are the most prescribed silvicultural treatments for management of eastern white pine insect pests and diseases (Ostry et al, 2010;Livingston et al, 2019).…”

Potential Interactions between Climate Change and Land Use for Forest Issues in the Eastern United States

“…Outbreaks of several species of native insects (e.g., southern pine beetle, Dendroctonus frontalis; red oak borer, Enaphalodes rufulus) and fungi (e.g., fusiform rust, Cronartium quercumm f.sp. fusiforme; oak wilt; Ceratocystis fagacearum) that attack trees consistently occur in current forests with high densities and basal area [97], which typically are greater than in historical forests that had low tree densities due to frequent fire. While increased tree densities occur regardless of climate variation, greater water availability ameliorates stress on trees, particularly in high density stands.…”

“…Reducing additional stressors, such as risk of insect outbreaks, and competition for limited resources will help trees survive and thrive under climate change. This may be accomplished in part by restricting tree densities [96,97].…”

Modeling climate-smart forest management and wood use for climate mitigation potential in Maryland and Pennsylvania

“…The climate change impact scenarios suggest that increases in disturbance intensity and severity could counteract any projected increases in future growth caused by climate change resulting from carbon fertilization, warming temperatures, or longer growing seasons (Kurz et al, 2008). Additionally, evidence suggests that risk from wildfire, insect and pathogen, and drought disturbances pose a severe future threat to carbons storage (Allen et al, 2015;Jolly et al, 2015;Brando et al, 2019;Walker et al, 2019;Asaro et al, 2023). Therefore, focusing exclusively on C sequestration and storage cannot supplant other management goals such as enhancing forest health and resiliency without potential catastrophic repercussions for future ecosystem resilience.…”