Forest Health

There are many definitions and opinions about what is meant by “forest health.”

Our Definition

A healthy forest displays resilience to disturbance by maintaining a diverse set of structures, compositions, and functions across the landscape. Secondly, it is hoped that healthy forests meet the current and future needs of people in terms of values, products, and services. These two elements of a healthy forest are interrelated, but may oppose each other. A healthy forest may be able to meet societal needs indefinitely, but only with sustained ecological capacity to recover from human or natural disturbance.

Purpose & Goal

Utah's Forest Health Program contributes to a strategic Division goal to "provide for long-term sustainability of natural resources on non-federal forest, range, and watershed lands." The purpose of the Forest Health Program is to provide Division service foresters, community foresters, private landowners, and other partners with information, education, technical assistance, and appropriate management strategies to prevent pest epidemics and achieve healthy forest stand conditions.

Forest Health Monitoring

Forest Health Monitoring (FHM) is a national program designed to evaluate the status, changes, and trends in forest health conditions on an annual basis across all land ownership. The United States Forest Service is working cooperatively with state natural resource entities, as well as other federal agencies and universities, to implement FHM at four principal levels:

Detection Monitoring
Evaluation Monitoring
Intensive Site Monitoring
Research on Monitoring Techniques.

The purpose of this initial Utah Forest Health Monitoring report is to highlight the prominent forest health issues in the state and to provide a baseline summary of field plot and survey activities associated with Detection Monitoring. If unexplained changes are detected Evaluation Monitoring may be activated to investigate the extent and severity of changes. Intensive Site Monitoring involves a national network of sites for research on ecological processes related to elements of change in specific ecosystem types. Finally, Research on Monitoring Techniques is responsible for developing reliable forest health indicator measurements.

FHM reports forest-related health issues on a large scale. The principle levels of reporting are state, regional, and national/international. Local or special evaluations, surveys, and reports augment FHM data as necessary and are produced as issues arise and where FHM data sets are appropriate for the area of consideration.

Insect and Disease

In addition to fire; insects, diseases, and weeds act as important disturbance agents in Utah forest ecosystems. Fire suppression has altered the occurrence, severity, and intensity of fires. This may have contributed to increased insect and disease activity in certain forest types. Noxious and invasive weeds in Utah are spreading at an alarming rate, displacing native species and disrupting the normal functioning of ecosystems.

Insects and diseases play an important role in the function and nutrient cycling of forest ecosystems. In a healthy forest, endemic levels of insects and diseases remove weakened and stressed trees, thus thinning the forest and reducing competition for light, water, and nutrients. Dead trees provide habitat for a variety of wildlife species. For example, raptors use dead trees for perches and decayed trees provide homes for cavity-nesting birds. The vigor of trees is an important factor in determining their susceptibility to attack by insects or diseases. Forests that are over-mature or over-dense often become susceptible to insect and disease outbreaks, creating considerable fuel and increasing the susceptibility of stands to fire.

Bark Beetles (General): Bark beetles are among the most destructive pests in Utah’s coniferous forests. These small insects bore through the bark to create galleries where they lay eggs; their larvae then feed on the phloem, effectively girdling and killing the tree. While often part of a natural ecosystem, prolonged drought and dense forest conditions can trigger massive, landscape-scale outbreaks.

Douglas-fir Beetle Part of the Dendroctonus genus, this beetle specifically targets Douglas-fir trees, particularly those that are downed, injured, or stressed by drought. Reddish-orange boring dust in bark crevices is a primary sign of infestation. Because they can attack healthy trees during outbreaks, managing stand density is critical for forest resilience.

Emerald Ash Borer (EAB) Though a relatively new threat to the region, EAB is a highly invasive wood-boring beetle that is 100% fatal to untreated native ash trees. It is critical for Utahns to monitor for "D-shaped" exit holes and canopy thinning. Because ash is a common urban tree in Utah, EAB represents a massive potential economic and environmental loss for our communities.

Ips Engraver Beetle Ips beetles typically attack pine and spruce trees that are already stressed or weakened by recent transplanting or drought. Unlike some other bark beetles, Ips are known for their "Y" or "H" shaped gallery patterns under the bark and their tendency to produce multiple generations in a single warm season, leading to rapid localized spread.

Mountain Pine Beetle (MPB) Perhaps the most famous of the bark beetles, MPB attacks various pine species, including lodgepole and ponderosa. Large-scale MPB outbreaks can change entire landscapes, turning green forests to "red-top" within a year. Successful attacks are often marked by "pitch tubes"—blobs of resin the tree uses to try and push the beetle out.

Pinyon Engraver Beetle Specifically targeting Utah’s iconic Pinyon pines, this beetle is a major driver of mortality in woodland ecosystems, especially during periods of low precipitation. They usually attack the trunk and larger branches, causing the needles to turn a bright straw-yellow before fading to reddish-brown as the tree dies.

Spruce Beetle This beetle is the primary cause of mortality in Utah's Engelmann spruce forests. Outbreaks often begin in wind-thrown trees and then move into standing timber. Over time, spruce beetle infestations can convert old-growth spruce-fir forests into subalpine fir-dominated stands, significantly altering the forest composition.

Balsam Woolly Adelgid (BWA) An invasive wingless insect that targets subalpine fir, BWA injects toxins into the tree while feeding, causing "gouting" (swelling) of branch nodes and abnormal wood growth. Over several years, this disrupts the tree’s ability to transport water and nutrients, leading to crown dieback and eventual mortality in Utah’s high-elevation forests.

Black Pineleaf Scale This pest appears as small, dark, armored bumps on the needles of various pine species. By sucking the sap from the needles, the scale causes yellowing, premature needle drop, and a thin, "see-through" appearance in the canopy. Severe infestations can weaken a tree's vigor, making it more susceptible to secondary attacks by bark beetles.

Fir Engraver Targeting mainly true firs like white fir, the Fir Engraver creates distinctive horizontal galleries that can girdle the tree. Evidence of an attack often begins with "top-killing," where the uppermost branches turn red while the lower crown remains green. They are often "stress-led" pests, thriving in trees weakened by drought or root disease.

Pitch Mass Borer This clearwing moth larva creates large, unsightly masses of dripping pitch on the trunks of pines and spruces. While the damage is often aesthetic and rarely kills the tree on its own, the boring activity can weaken the structural integrity of branches and serve as an entry point for various fungal pathogens.

Poplar Borer A significant pest of aspen and cottonwood, the Poplar Borer creates large tunnels in the wood, often evidenced by "frass" (sawdust-like excrement) and oozing sap on the bark. Repeated attacks can cause structural failure or "snapping" during high winds, posing a safety risk in residential or recreational areas.

Western & Forest Tent Caterpillars These defoliators are easily identified by the large, silken "tents" they weave in the branches of deciduous trees like aspen and mountain mahogany. While the sight of a completely defoliated tree can be alarming, healthy trees usually survive the attack and will "re-leaf" later in the season, though repeated years of defoliation can cause dieback.

Western Pine Beetle This beetle specifically targets Ponderosa pines, particularly older or drought-stressed individuals. They create intricate, winding galleries that look like "spaghetti" under the bark. Like other Dendroctonus beetles, they use pheromones to coordinate mass attacks, which can quickly overcome a tree's natural resin defenses.