season of burn – Prescribed Fire

January 16, 2020January 21, 2020

Using Prescribed Fire to Enhance Habitat for White-tailed Deer

Prescribed fire is an excellent tool to stimulate and maintain forage and cover for white-tailed deer. Browse (the leaves and twigs of woody species) and forbs (broadleaf herbaceous plants) dominate the whitetails’ diet throughout their range, and fire can be used to increase available nutrition from these plants in woods and fields. Fire can also be used to maintain relatively dense cover before openness and visibility increase as a result of over-shading and competition.

Frequency of Fire

Forb production is highest in early successional stages where sunlight is not limited. In the eastern US, where rainfall exceeds 30 inches per year, woody species invade post-disturbance and typically dominate within 7 – 10 years, limiting forage available for white-tailed deer. Burning on a 3 – 7-year fire-return interval maintains early successional vegetation, which often provides 2,000 – 6,000 pounds (dry matter) of desirable forage per acre during spring and summer. This forage production rivals that of warm-season food plots and can be maintained at a fraction of the cost of food plots. The exact fire-return interval necessary varies by site and year. When managing for deer, it is desirable to burn when woody encroachment begins to limit forage production. This interval provides not only food, but attractive bedding cover as well.

Season of Burn

The fire-return interval influences vegetation composition and structure more than any other factor. However, timing of burning can also influence vegetation composition and associated structure. Within a given fire-return interval, burning during the dormant season sets back vegetation structure, but often does not change vegetation composition appreciably. Most woody species readily re-sprout following fire in any season. Burning during the growing season (especially late growing season) tends to decrease woody species and promote increased herbaceous coverage. Thus, the necessary fire-return interval to maintain the same vegetation structure and composition may be a year or 2 less following dormant-season fire than growing-season fire. Late growing season fire may encourage more forbs in areas where grasses represent >70% coverage. Increased forb coverage (>30 percent groundcover) is desirable when managing for deer. Browse and/or forbs should comprise 30 – 70% of the groundcover. Grasses are not desirable for deer forage, but some grass coverage provides fine fuel and facilitates burning.Both dormant- and growing-season fire have a place when managing for white-tailed deer. Although various browse species are selected over others by whitetails, browse re-sprouting following burning is highly nutritious. Young growth of any plant is more nutritious, more palatable, and selected by deer over older growth because it is more digestible. Nonetheless, as the growing season progresses and plants mature, forage quality declines.

Animal Nutrition

Fire can also be used in woods and woodlands to increase available nutrition and cover for white-tailed deer. However, burning in closed-canopy forests will do little to improve browse availability or fawning cover. Thus, it is important to open the canopy to allow at least 20 – 30% sunlight into the stand prior to burning. Retention cutting, thinning, and shelterwood harvests are often used to reduce canopy closure and enable more sunlight to enter the stand. Forage production (browse and forbs) in the understory of a closed-canopy forest usually averages 25 – 100 pounds (dry wt) per acre. With additional sunlight, forage production is increased to 700 – 1,000 pounds (dry wt) per acre. It is important to note these estimates only include plants commonly eaten by white-tailed deer, not total biomass. This flush of new vegetation not only increases nutritional carrying capacity, but also can help increase fawn survival by enhancing cover. The soft mast (such as blackberry and blueberry) response following fire also provides increased nutrition for deer.

If burning the woods may involve a little more than what it’s worth, consider this: Burning 4 acres of woods typically provides as much warm-season forage as 1 acre of soybeans. The increased forage following burning will persist at least 3 – 5 years, whereas warm-season food plots have to be planted each year. Any serious deer manager cannot afford to not consider using prescribed fire.

January 16, 2020January 21, 2020

Effects of Timing of Fire and Fire Intensity

Fire frequency (or fire-return interval) is the most important factor with regard to how prescribed fire influences vegetation composition and structure. Fire intensity and season of fire are two other factors that can also influence plant communities and thus wildlife communities.

Plant Succession

Managing plant succession is one of the main reasons managers use prescribed fire. Plant succession is the orderly process of plant communities changing following some disturbance event, such as fire, that leads to some final stage that is relatively stable until another disturbance event occurs. Whether our objective is to manage land for a particular wildlife species, ecological restoration, or increased forage for livestock, we use fire to influence the plant community. Fire can be used to set back succession or maintain a particular successional stage, and the effect of fire is influenced by how we use it. In general, and to a certain point, the hotter the fire, the greater the chance of killing vegetation. Most woody plants are killed when the cambium layer (the inner bark) reaches approximately 145⁰ F. Of course, all fires are hotter than 145⁰ F. However, tree bark is a good insulator and protects woody plants from many elements, including fire. Chances of raising the temperature of the cambium layer to a lethal temperature are increased with a hotter fire or by slowing the spread of fire (a longer residence time). It is important to understand that many woody stems may only be top-killed when the cambium reaches 145⁰ F. That is, the roots of the plant may continue to survive and the plant will sprout from the roots.

Fire Intensity

Fire intensity is influenced by environmental conditions, such as fuel load (amount of leaf and grass litter), litter moisture, litter size, air temperature, relative humidity, and wind speed, as well as the firing technique used. Fire intensity can be controlled by burning within certain environmental parameters and by using certain firing techniques. Within a given set of environmental conditions, headfires are hotter than backfires (headfires move with the wind and backfires move against the wind). However, the residence time of a backfire is considerably longer than that of a headfire. Thus, it is possible for a slower moving and less intense backfire to heat the cambium layer of a small tree or shrub to a higher temperature than a hotter and faster moving headfire. It is also generally safer to use a backfire than a headfire becasue a backfire is slower and typically has shorter flame lengths. Nonetheless, a relatively hot headfire is normally required to kill relatively large (>4 inches ground diameter) woody stems because the bark is thicker on larger trees and more resistant to relatively cool backfires.

Fire Seasonality

Across most of the US, fire may occur in any season. Although late winter is when most people implement prescribed fire, considering other times of the year will not only extend opportunities for burning, it could also influence plant composition and help meet land management objectives. In general, research has shown that within a given fire-return interval, burning during the growing season (especially the late growing season) tends to kill woody species and decrease woody composition more than burning during the dormant season.

It is interesting how fire intensity may be greater, on average, when burning during the dormant season than during the growing season, but the effect in killing woody species is greater when burning during the growing season. Fuels tend to be drier and burn hotter during the dormant season than the growing season (the exception being during summer drought conditions). However, greater fuel moisture content during the growing season also means a longer residence time. Thus, timing of fire and fire intensity can be related.

It should be clear that fire frequency has a greater influence on plant composition and structure than timing of fire. However, prescribed fire does not have to be implemented during the dormant season. Consider burning during other seasons of the year and adjust fire intensity to help meet land management objectives.

January 16, 2020January 21, 2020

When is the Best Time of Year to Conduct Prescribed Burns?

One of the main questions many land owners and fire managers often ask about prescribed burning is when is the best time of year to burn? This will vary depending upon specific land management goals. Timing will also depend upon when the burn can be accomplished safely and under favorable weather conditions. When planning prescribed burns it is important for fire managers to know and understand how many days are actually available during a specific season or over the entire year. Knowing this will allow fire managers to plan for and execute a predetermined number of burns during a given year. It can also aid in determining in which season or seasons it may be best to conduct their burns.

Limited Number of Burn Days

Most fire managers have several prescribed fires to conduct during a specific burn season, and if an adequate number of days are not available, some burns will not be conducted that year. Burns not conducted are usually postponed until the next year, adding more burns and needed burn days to an already limited schedule the following year. It can also drastically change management plans on that particular burn unit. More often than not, many burn units are not burned regularly or at all because of a limited number of burn days due to restricting burning during a traditional burn season. This can negatively impact resources in numerous ways, along with creating an increased work load and cost on fire managers trying to implement prescribed burns.

Because of the limited number of burn days, a fire manger may try to burn when conditions are marginal. This can result in a prescribed fire that is not as effective as it should be causing management goals to not be met. On the other hand, safety may be compromised when prescribed burns are performed under marginal or less than desired conditions because of the need to complete all of the planned burns during that traditional time frame. If prescribed fires were conducted year-round, then more days would be available for burning, and the most optimum days for achieving goals and safety could be used.

Weather Variables

Weather has a major impact on prescribed fires and associated fire behavior. Therefore, the number of days available to burn each year is constrained by weather variables such as: temperature, wind speed, and relative humidity. Achieving the prescribed set of weather conditions during a particular time of the year has always been a dilemma faced by fire managers. If the goals of the prescribed burn are not extremely specific and safety concerns are maintained, then a wide range of conditions can be used for temperature, relative humidity, and wind speed. Often, a narrow window of weather parameters is required due to safety issues, policy, and regulation, which will reduce the number of available burn days.

Even if weather conditions can be met, timing of the prescribed burn is often limited to a single season by policy, tradition, or a lack of understanding of fire effects. Again, this limits the number of available days left to conduct prescribed burns. Remember that historically, fires occur throughout North America at any time of the year. Records show that fires set by Native Americans occurred in nearly all months, with a majority in the late summer. Also a majority of the lightning-caused fires in many regions of the United States occur during the growing season. In many areas burn season is late winter to early spring to correspond with green-up for livestock production, which also coincides with highly variable and changing weather conditions. However, conditions during the later winter can be favorable for wildfires which will further limit to the number of available burn days.

Limiting burning to a single season will continue to severely limit the application of prescribed fire in many areas. Also the lack understanding fire affects on native plant communities will also reduce the seasonal opportunities for conducting prescribed burns.

There are several publications and videos available that can assist fire managers to better understand fire prescriptions, fire effects and the best time to burn.

The Best Time of Year to Conduct Prescribed Burns http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-7504/NREM-2885web.pdf

Fire Effects in Native Plant Communities http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2703/NREM-2877web.pdf

Fire Prescriptions for Native Plant Communities http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2704/NREM-2878web.pdf

The Impact of Fire on the Landscape SunupTV http://www.youtube.com/watch?v=xh7_onVw8PQ&feature=plcp

Prescribed Burning for Pasture Management SunupTV http://www.youtube.com/watch?v=jq0XAsWq8Ok&feature=plcp

January 16, 2020January 21, 2020

What time of the year should I conduct a prescribed burn?

Prescribed fires can be conducted year-round anytime land or habitat management objectives can be safely achieved.

Historically, fires occurred throughout the year in North America, although for most locations, fire was more prevalent during specific seasons. Trying to burn during these historic fire seasons can be problematic for some locations because of safely concerns and limited days when weather conditions fall within prescription. However, burning outside of the historic fire season does not preclude the ability to meet management objectives in most cases.

For more information about season of burn or the time of year to conduct burns, see The Best Time of Year to Conduct Prescribed Burns.