How to Use Growing-Season Fire in Hardwoods for Better Deer Habitat

April 24, 2024 By: Craig Harper and Mark Turner

More land managers are using fire to manage habitat for deer and other wildlife today than at any time in the past century. And for good reason. There is no other tool that can improve and maintain both food and cover for deer better than fire. 

Land managers typically use fire to maintain old-fields, grasslands, and other early successional communities, and to manage pine woodlands and savannas. Use of prescribed fire is common to manage these plant communities throughout the South and Great Plains, but far fewer land managers use fire in hardwood forests of the eastern United States. We are pleased to see that times are changing.

Fire in Hardwoods

For decades, fire has been taboo in hardwoods. Most foresters over the years have maintained that fire could not be used in hardwoods because fire kills or at least injures overstory trees. Well yes, you can kill hardwoods if you use fire, but you also can kill pines with fire. The difference is in intensity.

Simply put, most of the Southern yellow pines (longleaf, loblolly, shortleaf, pitch, slash, and table mountain) tolerate low- to moderate-intensity fire very well, and some of them require fire for regeneration. However, all hardwoods in the eastern United States are less tolerant of fire than these pine species. 

So, over the years, fire practitioners have become accustomed to using relatively hot fires when burning pine stands and grasslands, and when they use a similar burning approach in hardwood stands, they damage or kill many of the overstory trees, including oaks, which is the most important group of hardwood species for deer and many other wildlife species.

Hardwoods are most easily burned in the dormant season, but recent research is showing how fire can be used at other times of the year to influence understory composition and structure, influence deer use, and provide necessary resources for deer year-round. 

Burning during different seasons may produce different effects on vegetation and the resulting habitat quality for deer. Differential effects may be related to timing or they may be related to fire intensity. For example, burning during the early portion of the growing season produces fresh-sprouting, highly nutritious forage during mid-summer when the nutritional demand is greatest for lactating does and bucks growing antlers. Conversely, burning during the latter portion of the growing season may affect understory composition and structure differently and thereby influence deer food and cover availability differently than fire during the dormant season or early portion of the growing season. 

Low-intensity fire in hardwoods can be applied safely during the growing season, but you can expect differences in intensity based on timing. When we measured maximum burn temperature using data loggers, we documented early-growing season (EGS) fires were hotter than late-growing season (LGS) fires. The cooler fires in the late growing season did not burn as completely and left more stems which resulted in an overall taller understory structure.

Early vs Late Growing Season

Throughout this article, we will refer to “early” vs “late” growing season for fire timing. The exact timing of early and late growing season will differ based on your location. We generally consider April to early May to be early growing season in the Mid-South, after leaf-out has begun but before leaves on overstory trees are fully developed. Our late growing season burning primarily occurs during September and October, often just before or during the period when leaves are changing colors. 

What About Turkey Nests?

Many of you reading this are managing your properties for turkeys as well as deer, and there is concern among many folks that burning during the early growing season is detrimental for turkeys because of destroying nests. Risk of destroying nests is lessened by not burning large acreages during the early portion of the growing season. 

Our research has detected increased use by foraging turkeys soon after burning. Brooding hens during summer may selectively use stands burned just a couple months prior over stands burned the previous growing season because of the shorter vegetation structure and increased visibility for the hen. The taller structure promoted by fire during the latter portion of the growing season may promote improved structure for nesting. As long as you don’t burn at too large of a scale during the early portion of the growing season, fire during both seasons can promote resources to benefit turkeys as well as deer. 

Matching sunlight with fire frequency

The primary limiting factor for understory response is sunlight. Generally, a minimum of 30% sunlight is needed to promote considerable understory response, which means you must reduce canopy cover by cutting or killing trees. Increased and faster understory growth is realized when more than 50% sunlight enters the stand. Your objectives determine the level of canopy disturbance and available sunlight. 

  • If you want to increase understory structure with moderate amounts of forage and maximize mast production, you should allow approximately 30% sunlight into the stand while retaining good mast-producing trees. Using low-intensity prescribed fire every two to four years will maintain this structure and forage availability on most sites. 
  • If you want to maximize forage production, you should allow more than 50% sunlight into the stand and use low-intensity fire every one to two years. 
  • If you want to maximize cover, you should allow more than 50% sunlight and use moderate-intensity fire every four to six years, burning before regenerating stems grow to about 3 inches in diameter at ground level. 
Late growing-season fire (September/October) in a hardwood stand. Recent research is showing how fire can be used at other times of the year to influence understory composition and structure, influence deer use, and provide necessary resources for deer year-round. 

Commercial Timber Harvest

A commercial timber harvest may be used to reduce canopy cover in stands with commercially desirable species of sufficient size and acreage to entice loggers to harvest the trees. However, commercial harvests can be problematic by damaging retained trees while extracting harvested trees and by rutting the site with heavy logging equipment, which many landowners find highly undesirable. Such negative consequences can be lessened by stipulating certain requirements in the contract and by contracting conscientious loggers. 

Most importantly, any thinning should reduce prevalence of undesirable trees and especially those competing with desired species to allow additional growing space and sufficient sunlight (30 to 50%) to the forest floor to stimulate understory response. We stress that such cuts should reduce prevalence of undesirable trees and retain desirable trees. This is very different from “selective harvests” that incorporate a diameter-limit harvest (such as harvesting trees 14 or 16 inches diameter-at-breast-height and larger). Such cuts high-grade the stand and severely reduce future timber value as well as habitat for deer and other species, such as wild turkey. 

Generally, thinnings implemented for deer should cut or kill trees species that do not provide deer food as well as individual trees of desirable species that have poor form or canopy position and are competing with trees with better form and position in the canopy.

Shelterwood With Reserves

If you are interested in regenerating the stand, then you should consider a shelterwood with reserves. This regeneration method removes undesirable species as well as individual trees of desirable species as needed to promote increased volume of retained trees, called the overwood, while allowing increased sunlight to the forest floor. A shelterwood with reserves differs from a traditional shelterwood in that the retained overwood is harvested approximately six to eight years later with a traditional shelterwood.

The retained overwood in a shelterwood with reserves is left in the stand to provide mast (usually acorns) for deer and other wildlife in the presence of relatively dense regenerating stems. Young regenerating stems of most oak species in the eastern United States are intermediate in shade tolerance and respond favorably to about 30% sunlight, which limits competition of shade-intolerant species. If dense regenerating stems are not desirable, and increased natural forage is the primary objective, frequent low-intensity prescribed fire is implemented to maintain forbs and fresh browse for deer.  

Forest Stand Improvement

If you are not interested in a commercial harvest, or if the trees to remove will not pay their way out of the woods, then you can use Forest Stand Improvement (FSI) techniques to open the canopy and influence food and cover for deer. 

Using either girdle-and-spray or hack-and-squirt, you can transition tree species composition by reducing undesirable species and retaining desirable species. Tree spacing does not have to be even. 

We promote “variable retention” when implementing FSI, which creates variable structure in the overstory and understory. In areas of the stand where more desirable species are present, we typically retain more trees; where undesirable species are more prevalent, we kill more trees. This approach creates more diversity in understory species composition and structure. 

Low-intensity fire then can be used to maintain deer forage or cover. Fire frequency influences species composition and structure whereby more frequent fire is used to maintain high-quality forbs and fresh sprouts, and less frequent fire is used to maintain relatively dense small-diameter stems (less than 2 inches DBH) to promote bedding cover.

Canopy reduction paired with early-growing season (EGS) and late-growing season (LGS) fire resulted in increased understory cover, but LGS fire promoted better fawning and bedding cover compared to EGS the summer immediately after both fires. The difference in cover is directly related to intensity and time-since-fire.

Forage and Fawning Cover

It is well-documented that canopy reduction when paired with fire may increase cover and forage for deer. However, the effects of burning during different times of the year have only recently been documented. Regardless of season, burning will promote more forbs, grasses, and resprouting brambles, shrubs and trees than in closed-canopy, unmanaged hardwood stands. 

Our research has documented that you can expect an average increase of 500% more deer food if you allow at least 30% sunlight to enter the stand and follow that with burning during any time of year. However, you can expect differences when burning during different seasons. Most importantly, burning during the dormant season and early portion of the growing season tends to be more intensive, and a hotter fire will top-kill a greater portion of hardwood saplings than a less-intensive fire. Vegetation resprouts following dormant- or early growing-season fire, but the response following early growing-season fire is several weeks after that of a dormant-season fire, thus highly nutritious forage is extended into late spring and early summer when nutritional requirements for deer are greatest.

In general, burning during the latter portion of the growing season is less intensive because of the greater biomass of green leaves, which are predominately water, and overall shade effect compared to burning during the dormant season or early portion of the growing season when near-full sunlight is reaching the forest floor. Thus, more hardwood saplings and bramble stems may escape fire during the latter portion of the growing season because the fire does not spread as easily and does not top-kill some stems. 

A cooler fire that does not burn the area completely may lead to increased browse and better cover for fawns because all of the vegetation was not top-killed, but overall forage quality will be lower because there is less fresh resprouting vegetation. If conditions permit a hotter fire during the latter portion of the growing season, hardwood stems and brambles may be set-back equally or better than during early growing-season fire, and more forbs may be promoted than burning at other times of the year. Forage quality for deer is outstanding the following spring, but quality slowly declines as the vegetation matures through the growing season. 

Thus, you can see how burning at different times of the year on your property stimulates and makes available highest-quality forage throughout the growing season. Plus, it allows you more burn days.

Early-growing season (EGS) and late-growing season (LGS) fire plus canopy reduction both increased forage biomass, but EGS improved availability of high-quality forages which resulted in an increase in nutritional carrying capacity, which relates to the number of deer that can be supported at a particular nutritional constraint.

If you haven’t burned before, or haven’t burned much, you likely are hesitant to use fire because of your lack of experience. That is a good thing! We should always use fire with some hesitancy and with extreme caution, just like we should exercise extreme caution anytime we are driving an automobile or tractor. That said, burning hardwood stands during the mid- to late growing season is an excellent time to get additional burning experience because typical conditions are relatively moist and fire intensity is low. In fact, on a typical day, it will be difficult to get the stand to burn at all. Of course, if you haven’t burned before, we recommend you have someone with burning experience to help you. Contact your state’s forestry agency and prescribed fire council to learn about support and training resources.

Deer Response and Spreading Fire Around

Burning during different times of the year can strongly influence deer use of an area. As fresh, resprouting vegetation becomes available after burning, deer preferentially select these areas for foraging. Our research indicates the increased use begins as soon as fresh vegetation appears and lasts for about two months. Thus, to best extend optimal deer forage across your property, you would conduct some burning during the dormant season to provide fresh resprouting vegetation in spring. 

Then, you would burn another area(s) during the early portion of growing season to extend high-quality forage into mid-summer. You then would follow that with burning another area(s) in the mid- to late portion of the growing season. Burning hardwood stands during the mid-growing season can be difficult because of the relatively moist fuel conditions. 

Typically, you will need more than 50% sunlight and a little wind to help carry the fire. However, we routinely burn in the latter portion of the growing season as conditions get drier. You simply have to be prepared to burn when conditions permit.

The areas you burn do not have to be large. In fact, we promote burning relatively small areas (5 to 20 acres, or even smaller). If you have your woods and fields broken into sections with firebreaks, you can easily implement such a strategy and better distribute high-quality forage throughout the property over time. Multiple units can be burned the same day. However, because you are implementing fire throughout the year, you don’t have to get everything burned at once! 

You Can Do It

Yes, you can burn hardwood stands without damaging or killing desirable overstory trees. Low intensity, coupled with removing any large debris from the base of the tree, is the key. Timing also is highly influential. Burning at different times of the year and adjusting the amount of sunlight entering the stand will help you increase food and cover resources for deer and other species on your property. 

You can do it! Start small and spread your management out across your property and throughout the year. You may just find that you don’t have to plant as many food plots as you thought, and you certainly don’t need to fill up the feeders!

About Craig Harper and Mark Turner:

Dr. Craig Harper is the Extension Wildlife Specialist and professor of wildlife management at the University of Tennessee and a Life Member of NDA. Mark Turner is an NDA member and Level 2 Deer Steward who is currently a Ph.D. candidate at the University of Tennessee working under the direction of Dr. Craig Harper.