Prescribed fire is one of the most useful deer habitat management tools. In our experience, members of the National Deer Association are well-versed at this point in prescribed fire’s benefits. However, there are still some barriers to using prescribed fire, and in this article we will concentrate on one that receives little attention – risks of burning in upland hardwoods, and how potential loss of hardwood timber value compares to the value of deer forage produced.
Mortality to mature hardwoods as a result of prescribed fire is rare. Despite this, concerns surrounding effects of prescribed fire on hardwood sawtimber value are common. In fact, the most common barrier for landowners when considering whether or not to burn in upland hardwoods is the fear of losing sawtimber volume or value, particularly of oaks. If more habitat managers were comfortable with using prescribed fire in hardwoods, the use of this technique would grow in regions and states where it is being under-utilized now.
As managers of our own upland oak stands for deer, we were curious to uncover the actual risks of using prescribed fire in upland hardwoods and how the cost:benefit compares to other management practices like food plots and supplemental feed. So, we conducted a full review of previous research to dig up all the data we could find on this topic, and we calculated a cost:benefit ratio based on those results.
First, let’s think about factors that reduce the value of hardwood timber.
How Fire Causes Value Loss
Various defects are common in upland hardwood forest stands across the United States. In fact, the U.S. Forest Service describes around 40 different potential defects that can reduce the value of hardwood timber. Common examples of such defects are seams, catfaces, knots, burls, and of course butt-scars, some of which can result from fire damage.
Factors influencing fire scarring are related to species composition, fire intensity, seasonality, and site. The threat of fire scarring and scar size is substantially reduced in larger, thick-barked tree species. Additionally, the probability of fire scarring is higher on southern aspects and steeper upper slopes and ridgetops where fire intensity may be higher than on northern aspects, cove sites, and flat terrain.
Growing-season fires have a greater potential to cause scarring because trees are actively growing and ambient temperatures are closer to lethal temperatures that cause plant tissue necrosis. Fortunately, when using prescribed fire, you have the ability to make decisions regarding firing technique, fuel loading, site selection, and weather conditions to restrict fire intensity to safe levels and minimize scarring.
Reviewing the Science on Fire Cost
One of the most comprehensive studies to date was published in the Journal of Forestry in May of 2020 (Mann and co-authors, 2020). In this study, researchers evaluated the economic impacts of prescribed fire on sawtimber volume and value in 139 stands ranging from 10 to 50 acres in size in Hoosier, Mark Twain, Wayne, and Daniel Boone National Forests (Indiana, Missouri, Ohio and Kentucky respectively). Stands received anywhere from one to six prescribed fires over the course of 25 years. There were a few key findings that helped shed light on our questions.
Note: We refer to “butt-logs” here, which is a forestry term for the lowest 16-foot section of a tree above the stump and the section of a tree that has the highest dollar value.
There was a wide variation in the timber volume lost on butt-logs, which was due to differences in firing techniques on one of those sites. Three sites were using low intensity prescribed fires, those that you most likely use to manage for deer while preventing damage to the overstory. On these three sites, relative butt-log losses averaged between 0.9 to 2.1%, and stands that received four or more fires in the 25 years averaged around 5% butt-log value lost.
On the fourth site, the objective of burning was to shift forest composition to fire-dependent oak woodlands which required more intense firing techniques. In other words, the objective was to intentionally damage or kill less-fire tolerant species with fire, many of which do have commercial value. Thus, this site should be viewed as a worst-case scenario. Losses in the worst-case scenario averaged 10.1% value lost to the butt-log over the 25 years. On average across all four study sites, stands receiving four or more fires in the 25-year period lost $83.79/acre in the final timber harvest.
These findings were consistent with a study published by Marschall and co-authors (2014) who reported an approximately 10% value loss to red oak butt logs harvested from sites in the Missouri Ozarks receiving either three or four prescribed fires. Again, the objective of fire on this site was to restore open woodland conditions and more intense fires were used in these stands than would be when managing for deer.
Even so, when taking a closer look, they reported that lumber quality and volume of trees that had a fire scar were negligible (less than 5%) when harvested within five years of fire, but increased to 10% if harvested 14 years after fire. Importantly, this study was providing the loss on a tree that was injured, not the loss calculated across the entire stand which included many trees without injury despite the high fire intensity. To drive this point home, they also reported that scar height was a major factor in volume loss with virtually no losses occurring when the fire scars were less than 2-feet high, indicating minimal to no damage resulted from low-intensity fires.
As is logical, the majority of value loss to a tree, if any, from prescribed fire results from damage near the base of the butt log, leaving much of the remaining merchantable wood unaffected. When considering whole tree value, Wiedenbeck and Schuler (2014) found that log value loss was less than 1% for any species harvested from a site treated with two prescribed fires in West Virginia. Another related study, Stanis and co-authors (2019) reported an average of less than 3% loss in timber value across 54 oak-dominated stands experiencing various burn histories across sites in southern Indiana. This study also determined that stands with four or more fires averaged 6% loss of butt-log volume for all merchantable species.
Cost Per Pound of Deer Forage
At the end of the day, we are all asking ourselves “Is it worth it?” We have learned over the years the effectiveness of thinning (through commercial harvest or with Forest Stand Improvement) and burning to create a valuable combination of increased nutrition, cover, and attractiveness for deer on our hunting land. Is the value gained in pounds of forage, nutrition, fawning cover, or bow-stand encounters enough for us to increase the use of fire in our hardwood stands? We decided to do the math and compare the cost of increasing available forage by burning hardwoods to other activities many of us already practice.
We wanted to give you a conservatively high cost of producing protein by burning in upland hardwoods so we considered how much native forage can be produced with the added costs of contracting the burning and taking the value losses estimated from the above-mentioned studies.
Lashley and co-authors (2011) showed high-quality summer deer forage available following prescribed fire in hardwoods with adequate sunlight availability (greater than 30% canopy opening) was approximately 625 lbs./acre. Common deer forages in burned hardwoods (forbs, brambles, and woody sprouts) in the eastern United States regularly average 16% or more crude protein. In other words, burning in hardwoods can realistically produce 100 lbs./acre of protein for deer.
In general, contracted prescribed burning using a state forestry agency is approximately $30/acre. Let’s assume that you successfully use low-intensity fire most of the time but the fire intensity gets hotter than you would like 25% of the time, that should produce losses of about $84/acre similar to the Mann study (value lost averaged over three sites with low-intensity fire and one with high-intensity fire). However, those were fully stocked stands, so you would remove some merchantable timber before it was exposed to fire. For ease of numbers, we will assume stands were thinned to half the density, which results in half as many trees exposed to fire and half as much value lost per acre: $42.
In the first year, that equates to $0.09 per pound of forage and $0.57 per pound of protein produced. If we plan to continue burning on a three-year rotation for 10-years ($90), maintaining an average of 625 lbs./acre of deer forage per year, the cost drops dramatically to $0.02 per pound of forage and $0.09 per pound of protein produced.
Warm-Season Food Plots
A well-managed warm-season deer food plot with soybeans or cowpeas can produce around 8,000 lbs./acre of dry weight deer forage per year averaging 30% (2,400 lbs./acre) crude protein (Harper 2016). The cost of establishing food plots typically runs an average of $325/acre when considering average costs for lime, fertilizer, seed, and herbicide, not including costs for equipment, fuel or labor. In a single year of managing a warm-season food plot for deer, the cost breakdown is approximately $0.04 per pound of forage and $0.13 per pound of protein produced. When we extrapolate that cost over a 10-year period ($3,250) the average annual cost per pound of forage and protein remains the same.
Another common technique used to increase protein availability to deer is supplemental feeding. Common deer feed blends cost somewhere in the neighborhood of $25 per 50-lb. bag with approximately 20% crude protein available. That works out to $0.50 per pound of forage and $2.50 per pound of protein.
The Cost-Efficiency Winner
Now let’s put those costs into perspective. Even after taking conservatively high losses on timber value, burning in hardwoods to produce deer forage costs less than a warm-season food plot. Providing protein via supplemental feeding cost 27 times as much as burning hardwoods. Plus, these estimates do not include the financial gains from the timber harvest, or the added habitat bonuses of soft-mast production during the summer, increased hard-mast production in the fall, nor the added value of bedding and fawning cover.
Burn Hardwoods Even More Effectively
Our cost:benefit analysis shows that burning in hardwoods to improve habitat quality for deer is a cost-efficient way to increase available nutrition even if some losses in timber value occur.
If you are interested in using prescribed fire for this purpose, several thoughts should be kept in mind.
Based on previous studies, white oaks were less susceptible than red oaks which were less susceptible than other merchantable species. Thus, when planning a timber harvest, preferentially leaving more fire tolerant oak species may help minimize damages caused by burning. Luckily, those same tree species tend to be high value for deer.
Also, our cost estimates were conservatively high because they included a site that was using fire with the intent of damaging some overstory trees. Using low-intensity firing techniques such as backing fires and spot-firing techniques will result in far less damage to overstory trees.
In fact, previous studies show that almost all the damage to overstory trees following fire in upland hardwoods is attributed to limbs or downed trees catching fire next to the bole of a standing tree. Taking the additional precaution of removing this debris away from the base of prized trees can result in virtually no damage to the overstory from prescribed fire.
If you were interested in burning in your upland hardwood stand but losing money on timber value was a barrier, we hope this review and cost:benefit exercise has helped you put those risks into perspective and can help you make informed decisions about habitat management tradeoffs on your property.
About the Authors: Dr. Marcus Lashley is a professor of game management, Director of the University of Florida Deer Lab, and host of the Fire University podcast. Jordan Nanney is the Director of Field Operations for Compass South Forestry.