Wyoming Wildlife - March 2023

Conifer Control

Conifers encroach in a riparian area in sagebrush habitat. Habitat managers take many considerations when removing conifers to improve habitat for wildlife.

The Wyoming Game and Fish Department uses several techniques to control the spread of these trees and plants to improve and restore wildlife habitat

Willow Bish
3/1/2023 12:00:05 AM

The Wyoming Game and Fish Department’s habitat biologists work across many different types of habitats to implement restoration or improvement projects for the benefit of wildlife. Of all the different types of treatments Game and Fish conducts, one treatment is often noticed by the public — the removal of conifer trees and shrubs. People may wonder why these projects take place, especially in a state where trees are sometimes few and far between.

Conifer removal helps the growth of aspen stands, which benefits many species of wildlife like mule deer. (Photo by Mark Gocke/WGFD)

These kinds of projects are for the benefit of wildlife and habitat, and biologists make several considerations when planning and conducting these treatments. Experts review everything from the location, types of vegetation targeting, methods and tools used, time of year, weather and even down to how cut conifer material is dealt with after the treatment to ensure wildlife gets the most benefit from these actions.


Conifers, which are plants that bear their seeds in cones or modified cones which look like berries on juniper trees, typically have needle or scale-like leaves and are usually evergreen. Most conifers are trees, but there are conifer shrubs as well. Wyoming has 12 species of conifer trees, including subalpine fir, Utah juniper, Rocky Mountain juniper, white spruce, Engelmann spruce, blue spruce, whitebark pine, lodgepole pine, pinyon pine, limber pine, Ponderosa pine and Douglas fir.

Historically, periodic wildfires swept across portions of the landscape resulting in an ebb and flow of conifer tree density and distribution. But beginning in the 1800s and throughout the early 1900s heavy livestock grazing occurred, which reduced grasses and other vegetation that acted as fine fuels for fires to the extent it reduced the occurrence of wildfire. While many livestock operations have greatly improved their grazing management, active fire suppression now occurs. Fire suppression allows conifer trees to expand into areas where they would not normally occur, such as grasslands and shrublands, and allows for increased density of conifer trees in forested areas. The expansion of conifers, particularly into areas where it is undesirable, is called conifer encroachment.

Habitats are limited in resources, such as water, nutrients, sunlight and space. When conifers encroach they compete for resources with other vegetation. In many cases, this reduces habitat quality for wildlife. Conifers can out-compete deciduous, woody vegetation such as aspen trees, cottonwood trees and fruit-bearing shrubs, which are valuable for many wildlife species. Habitat managers are most concerned about conifer encroachment in riparian areas, aspen, shrubland and sagebrush/grassland habitats. Conifer encroachment can impact the value of forage in these habitats for species like mule deer and elk by directly competing with more desirable forage. It also can cause avoidance of habitat in the case of sagebrush/grasslands by species such as pronghorn, sage grouse and bighorn sheep because these species depend on the visibility provided by open habitats to scan for predators. Conifers increase the availability of perches for avian predators, which may further negatively impact species like sage grouse.

Conifer trees also impact the fuel loads within habitats, causing fires to burn hotter over larger areas than what they have historically. In many habitats periodic wildfire is beneficial. Some plant communities including aspen and some shrub communities such as true mountain mahogany and mountain big sagebrush depend on occasional disturbances such as fire to trigger new seedling growth or rejuvenation of plant material from the roots. However, when fires burn too severely soil sterilization can occur, and much of the native seed bank can be lost. This results in a prolonged recovery period and puts sites at risk of invasive plant species and erosion. Historic wildfires were more likely to be spotty, which leaves islands of unburned vegetation creating a mosaic across the landscape, which is generally beneficial for wildlife.

Conifer encroachment impacts habitat for wildlife, and this jackstraw method of conifer control is one way habitat managers reduce that impact on the land. (Photo by Willow Bish/WGFD)

Some plant communities, such as Wyoming big sagebrush in northeast Wyoming which grows in a low precipitation zone, respond poorly to fire. When these areas burn, sagebrush often does not naturally return — potentially for hundreds of years. This creates issues for species such as pronghorn, sage grouse and many nongame species. In these areas conifer encroachment from species like Rocky Mountain juniper can greatly increase the risk of fire due to the higher fuel loads.


Managers have several tools available for addressing conifer encroachment, including a variety of mechanical treatments and prescribed fire. When the proper conditions are met, prescribed fire can be an excellent, cost-effective method for addressing conifer encroachment that closely mimics natural disturbances. Prescribed fire may not be an option for all sites, because partnership with an entity that has a fire crew and burn authority is required. Sites also must have a low risk of having fire escape into areas outside of the targeted treatment. Treatments may have variable results as fires may burn hotter or cooler than intended. Liability also is a consideration on private land, especially in areas of intermingled land ownership. Prescribed fire isn’t recommended in areas like northeast Wyoming where damage to non-target species such as sagebrush is likely to occur. Also, the risk of invasive species occupying sites post-treatment influences decisions about what treatment method should be applied. In some areas prescribed fire may require post-treatment herbicide application to address invasive weeds. Burning is typically a better option for treatment on sites that receive higher precipitation and cooler weather, rather than dry, warm sites because of the low rate of recovery and higher risk of weed invasion on drier sites. Lastly, timing windows for burning may be extremely short, making it difficult to effectively plan and implement treatments. Unfortunately, due to the complexities involved with planning these projects and the lack of contractors available to conduct prescribed burns on private land, this method is not used as often as managers would like.

Mechanical treatments include chainsaw cutting and heavy equipment work. One of the more commonly used heavy equipment methods involves using equipment to grind tree material down. This method, called mastication, is effective at reducing fuel loads. It is a useful treatment method in areas where tree material needs to be reduced due to a high density of trees or for access reasons, such as for large herbivores, like cattle or elk, or humans. In some cases, the mulch left from mastication may be so thick that it inhibits understory vegetation. Mastication methods can’t be utilized in areas with difficult access, such as steep slopes, rocky areas, rough terrain or areas that are far from roads or do not allow for vehicles of any kind. Areas with moist soils aren’t the best candidates for heavy equipment work because there is a high likelihood of damage to vegetation and soil structure. Timing of treatment may minimize disturbance concerns by operating later in summer or early fall when the ground is drier or in the winter on frozen ground. Mastication may miss small trees, seedlings and low-lying branches which may require follow-up treatment or shortens the lifespan of the project. Heavy equipment methods can be costly and are not cost-effective on sites with low density trees.

Mastication is an effective method of conifer control where tree material needs to be reduced to a high density of trees. (Photo by Willow Bish/WGFD)

Chainsaw treatments are typically the most adaptable of all methods. They can be used on areas that are difficult to access with equipment and can be implemented with a high degree of precision to follow land ownership boundaries or to respect other restrictions. Timing of chainsaw treatments is typically flexible, which allows for a large window of treatment that effectively increases the amount of work that can occur each year. This method typically does not disturb soil or other vegetation and is often less disruptive to wildlife. Similar to heavy equipment work, this method may also miss small trees, seedlings and low-lying branches which requires follow-up treatment or shortens the lifespan of the project.


There are several techniques for cutting and handling tree material when utilizing chainsaw treatments. These include lop and scatter, cut and pile and jackstraw/hinging.

The lop and scatter technique involves cutting down trees and reducing the tree material so it’s closer to the ground. The vegetative debris left on the ground, called slash, can protect soil from erosion, provide microsites for increased moisture accumulation and protect desirable vegetation from excessive herbivory, or browsing by animals feeding on plants, by limiting access to the site for some time. Dense tree sites may result in too much slash, which limits understory vegetation growth. However, as trees break down and needles drop, understory vegetation growth becomes less inhibited. Similarly, the fire hazard may increase in the first few years before needles from the trees drop and the risk decreases over time. Lop and scatter can be cost-effective, but large trees and high tree density raises costs. This technique is often used in low-density sites. Lop and scatter is frequently used as a technique to prepare a site for future prescribed burns. Trees can be cut to create consistent ground fuels to effectively carry a fire through the site in order to stimulate aspen stands and produce a resprouting response.

Cut and pile treatments involve cutting trees with chainsaws or heavy equipment and then gathering tree material into large piles. Piles are left for several years and burned when they are dry and adjacent to areas not prone to burn. This method can be advantageous in areas where access through the site by humans and large herbivores is desired, or where fuel loads are too high to naturally decompose in a timely manner and specific boundaries need to be secured from the threat of fires, such as areas near infrastructure. This method is more costly than other chainsaw techniques and requires follow-up management for burning the piles and addressing weeds in areas where piles are burned. The increased cost associated with piling vegetation material is often not justified for habitat quality reasons alone and is often done for social reasons, human needs or the ability to have heightened control in adjacent prescribed burn areas.

This area of the southern Bighorns had limber pine encroachment, seen above. (Photo by Willow Bish/WGFD)

Habitat managers worked to reduce limber pine encroachment in this area of the southern Bighorns, as seen in this photo post-treatment. (Photo by Willow Bish/WGFD)

Jackstraw treatments involve cutting down trees and leaving them to lay where they fall without reducing the material. A variation of jackstrawing, called hinging, is when a felled tree is left partially connected to the stump. This treatment has similar implications for fire hazard as lop and scatter treatments, but the risk reduces over time. This treatment is cost-effective, which allows for a larger number of acres to be treated and is particularly useful in areas where herbivory is a concern, as it limits access to the site by herbivores for some time in order to allow for young, desirable vegetation to become established. Eventually, the trees break down and animals can access the site. This method is a more cost-effective way to protect sites than fencing due to the high cost and maintenance requirements of fencing. Jackstrawing/hinging is most frequently used in forested systems to protect species like aspen, which tend to be over-browsed by elk and livestock.

Decisions about conifer treatments can be complex, and require consideration of biological, technical, site-specific and social factors. The exact protocol may vary, but Game and Fish always has the same goal when conducting these treatments; to improve and maintain wildlife habitat. While some of these areas, such as open sagebrush/grassland habitats that have recently had a juniper lop and scatter treatment conducted, or an aspen stand that has had a variety of conifer species hinged/jackstrawed, may appear to be dramatically altered or result in a more difficult hike or hunt while trekking through the treatment, we hope readers now have a better understanding of the rationale behind these treatments and why Game and Fish does them.

— Willow Bish is a terrestrial habitat biologist for the Wyoming Game and Fish Department in the Casper Region. Terrestrial Habitat Program Manager Ian Tator, Game and Fish Migration Coordinator Jill Randall, Terrestrial Habitat Biologist Amy Anderson and Terrestrial Habitat Biologist Todd Caltrider contributed to this story.


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