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BY Richard Hines on Mar. 02, 2018

Prescribed Burning: Different Fire Strategies To Accomplish Various Goals

Across time, fires have dominated many ecosystems throughout the United States, particularly in the Southeast, Great Plains and the Appalachian Mountain Region. There is a definite history of fires not only in these regions, but every area in the U.S. Just as rivers routinely flood, fires would routinely burn large portions of the country. How often a fire burns on a site is called the “fire return interval” (FRI). In the southeast it would have not been unusual for sections of this region to burn annually or at least once every 25-35 years while some areas in northern Michigan may have had an average FRI of 200 years. It all depends on habitat type. This historical fire data was analyzed through examination of fire scars on old trees dating back into the early 1800s.

Today’s wildlife managers understand fire’s importance both to wildlife habitat as well as plant communities, and use it to closely mimic the original FRI. Knowing the past history of fire of an area will obviously be an important key in timing when to burn for fire dependent species. Land managers should consider all of these factors in deter-mining which fire strategies are best at accomplishing various goals and objectives. Fire can accomplish many tasks, not only to improve habitat, but when properly timed, to reduce fuel loads on the ground to decrease the potential for catastrophic wild fires.

What type of burning you should use will vary region to region and also among soil types, slope aspect, even the vegetation you are burning. Pine verses hardwoods verses grasslands, and even on grasslands cool seasons grasses verses warm season grasses all have varied responses. 

To begin, what are you trying to accomplish and what are your objectives? Keep in mind that different strategies may be needed to accomplish specific objectives and will influence which fire will be best. Some fires are used to just simply kill woody plants, improve native grass stands or “improve wildlife habitat.”  Every fire should have a plan with a clear objective that says; what you want to accomplish. One way to evaluate your success is taking photographs before and after the burn. Setting a metal T-post in a strategic location will identify a spot so you can evaluate the same place in coming years.

One of the most fire dependent game species is the northern bobwhite quail, so your burn might include improving grasslands for this bird. Important plants in the quail lifecycle include big bluestem, switchgrass or eastern gamagrass and forbs including partridge pea and all respond to burning. In managing grass-lands, your objective might include reducing hardwood stems growing up on the site. Without any control, hardwoods will soon take over a site, shading out grasses. In this case you should plan ahead by establishing fire breaks the previous fall.

Establishing firebreaks in the fall will help burning operations particularly if the soil is too wet to plow during late winter or early spring. In the South, you could also plant firebreaks with a green winter cover and this wide green cover will provide food for deer plus protect the soil from erosion. If you routinely burn areas, make some breaks a little wider so they can double as summer food plot locations.

Types of Fires

Once you select where you are going to burn, determine which type of fire is needed. In the world of prescribed burning three types of fires are used; a "backfire," "head fire," and "flank fire," and each type provides differing intensities for varying results.

The slowest and easiest to control is a “backfire” which burns into the wind. Flame length is sometimes so low you can step over the fire. However, that all depends on the fuel load on the ground. Fuel load is typically the amount of duff, leaves, dead grass on the ground – stuff that will burn. If you are burning slopes, this fire would be started at the top of the hill and slowly creep down slope. In most cases you can outwalk a backfire. Backfires are considered “cool” fires in that little damage is done to the larger trees. 

Ironically, because a backfire is slow the heat remains on site longer. This longer duration is perfect for killing smaller woody stems. It only takes 146° F to break the cambium on small trees, which is sufficient to kill them. If you are managing a native grass stand with woody encroachment, a back-fire may be the best way to knock it back. These cooler fires are normally ignited when air temperatures are less than 68°and relative humidity is more than 50%.

The opposite of a backfire is the “head fire.” These fires move up slopes at incredible speeds and even over flat ground the slightest wind will move flames rapidly over a site. Flame lengths are many feet long with extremely high heat which will push high into the canopies of trees. Because the heat is moving ahead so rapidly the fire is actually further drying the fuel ahead of the main fire, increasing the intensity of the fire. 

If you want to eliminate dense trees or shrubs such as cedar, a hotter fire may be needed. In these conditions you may be working in temperatures above 75° with relative humidity less than 30%. Needleless to say, this is a dangerous situation and should only be attempted by qualified fire crews. 

The third fire is a “flanking fire” which is set so flames move parallel into the wind. Flanking fires are also used to speed up backfires, but only after the burned section around the fire line (referred to as the black line) has widened sufficiently. Again fire training and knowledge of weather is important on flank fires.

Location of ignition points is always important. The primary ignition point should always be on the backside or area where the wind is blowing against the flame, pushing it into the firebreak. Experienced burners know to watch this first small flame as it indicates how the fire will behave. As the flame begins widening, each person with a torch moves the flame along the line keeping the backfire parallel, along the same line. At this point you want the firebreak widened by increasing the burned area or black-line. Move the fire across the entire backline and then begin edging up the sides after the blackline has increased. Communication between crew members is essential. 

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Seasons for Burning

Under correct conditions you can burn during any sea-son of the year, but obviously results will be different. Another factor to consider is the different amount of burn-days each month, plus you may only have a few hours each day that fall under the prescription parameters.

To ignite the ideal fire, it all gets down to weather and since the majority of ideal days come during late winter this is when most burning takes place. Because fuel is so dry during winter/early spring burns, they tend to consume everything across their path. Always consider how much cover you want to remove and only burn in small patches so some cover remains. Winter burns tend to favor grasses and may not have the impact on total woody cover removal unless woody vegetation is starting to green up. 

Spring and summer burns are also used but Jeff Hodges, National Grassland Coordinator for National Bobwhite Conservation Initiative says it all gets down to plant chronology, “From north to south there are slight differences in the best times to burn.” Typically burns late in the spring at the beginning of the warm season grasses’ growing season will give you pretty decent sprout control.” Hodges said that with late season burns there is also a risk of damaging nests of ground nesting birds such as quail, pheasant or turkeys. 

New quail research is debunking the previous thought that most birds are produced around June 15th.  It now appears that it is the second nesting attempt that produces the most quail for the year. In this case, burning during late July or August could be detrimental. So if you have to burn during this time only burn a small portion of the property. According to Hodges, “A nest may be lost, but when looking at the “big picture” you are improving habitat for the next two to three years.”

Overall, fire has very positive influence on wildlife. Daniel Boone National Forest Wildlife Biologist, Joe Metzmeier, told me their staff typically burns around 5,000 acres each year, primarily around pine stands and “these burn areas are magnets to turkeys.”  Metzmeier recalls seeing turkeys moving into and foraging over burn areas that still had smoldering logs from the previous day’s fire. Pre-scribed fire is one of the best turkey and deer management tools being used along the Cumberland Plateau Region. 

Another use of fire is eliminating invasive plants, but knowing your plants is vital. As an example, one of the most aggressive exotic plants in the Eastern US, is Sericea Les-pedeza. This introduction from Asia actually thrives with fire unless you burn during September when the plant is in full bloom. Again, type and timing of fires is important.

While burning in pines is a normal management technique, burning hardwoods has mixed reviews. Occasionally fire is used as part of fuel (ground litter) reduction, but using the wrong fire type during the wrong season can damage timber and reduce its value. If you manage oak savannah habitat, fire is necessary because many of the species such as bur oak and post oak are relatively fire resistant. Fire maintains the grass component of this habitat. Typically, woody species in this habitat have thicker bark plus the ability to compartmentalize wounds following a fire. White oak is also fairly fire resistant but any damage to the bole will greatly reduce timber value in coming years. Research is now ongoing to determine the proper type of fire and the FRI needed to help promote regeneration of oaks.

Ed Huffman, Professional Forester and owner of “Stewards of the Land” Forestry Service agrees and said there are some great uses of fire in forest management. “I am seeing some outstanding wildlife habitat in pines that are maintained in thinner stands, but my best use of fire is just maintaining old fields or general site prep for planting.” Huffman has seen some varied results from burning to promote oak regeneration and suggests it's best to get an opinion of a professional forester in your immediate region before using fire in valuable hardwoods. 

While fire has been around forever, it’s been used, mis-used, and in natural resources misunderstood more times than not, but properly used fire will work wonders for improving wildlife habitat enhancing forest conditions. 

If you burn your land you might consider hiring a professional to oversee the burn. If you conduct the burn yourself take time to obtain training. Typically, when I burn I begin watching the weather several days out searching for possible changes. The day of the burn I get final reports from local weather sources concerning the forecasts for relative humidity, winds, temperature and then I contact everyone on my burn plan. Even during the burn someone needs to be monitoring the weather. Experienced fire crews also learn to watch changes in the fire which may indicate changes in humidity or wind.

Several years ago a friend helped me with a small burn I was doing on my property. He said this is not what I thought it would be; it’s almost boring.” I told him that was a good fire! If everything goes as expected some folks may be wondering why they came, but trust me when conditions change abruptly you will need all hands on deck. That’s why proper planning is so essential. Many an impatient landowner has gotten bored and thought they could finish a burn up quick-ly by laying additional strip fires only to find themselves in trouble when humidity or winds shifted.

While it may sound difficult, learning how wind, air temperature and relative humidity all effect the environment and how fire will act during the burn is the best thing you could do if you are considering a prescribed fire for your property. Make sure you also meet with a Certified Wildlife Biologist or a Professional Forester. Let them work with you to determine goals and objectives that will benefit the wildlife and your timber resources.

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