Ranchers and rangeland managers sometimes use fire to retard invasive brush such as juniper or cedar and create more forage. In the process, this also reduces fuel loads to prevent catastrophic wildfires.
Chris Schenck, a statewide fire program leader with the Texas Parks and Wildlife Department, says historically fire kept rangelands and forests in properly functioning condition and ecological balance. “Really old climax systems [dominated by certain plants] are not as productive as a midserial system with wider variety of plants and more diversity,” he explains.
Schenck was with the U.S. Forest Service for 30 years and says fire is a good way to keep undesirable plant species in check; prescribed burns are one way to keep a balance of plants and ensure a healthy ecosystem.
When to burn
“Sometimes we wait until late morning when humidity goes down, so we can get more complete ignition and the fire will burn a little better. There’s less moisture in the fine fuels [grasses and small annuals],” says Schenck.
“An incomplete burn may not be a bad thing if our goal is to leave a mosaic with patches of unburned plants. Usually, however, we wait for the day to progress,” says Schenck. “On the other hand, if we’re worried about it being too dry, we start at the crack of dawn. Timing of fire during the day [or night] can give different results, but the main thing is getting the fire to carry or making sure it doesn’t carry too much, too fast. Often, we [are] hoping to be done by 3 p.m., and then we just watch it until dark. Sometimes wind comes up more strongly in the afternoon, and you might want to have the burn finished.”
Seasonal timing
Seasonality is important, depending on goals. “We typically burn in winter – dormant-season burning – when certain plants are dead or dormant due to frost, drought or their natural life cycle, and they are dry,” Schenck says. “With winter burning, we can reduce biomass, not only the fine fuels which usually carry the fire but also the medium (10-hour) fuels and the 100-hour fuels; we can reduce some of the woody invasive plants. With winter/dormant-season burning, we are often trying to kill heavy fuels like cedars or juniper and can usually get a good kill.”
“After dormant-season burning, we hope we receive precipitation and traditional weather cycles so we’ll get spring growth of desirable plants. Depending on how much time has occurred, spring growth could result in a return of annual forbs and shrublike plants that are good forage for wildlife or a return of good grass growth. The decadent old grass [that burned up] is not nutritious and impedes new growth.” It helps to remove that old grass along with the brush to allow more prolific growth of new grass.
Spring burning (or a bit later in the dormant season) is another option, with other goals. “There is still a lot of dormant or dry material, but we’re starting to see annual plants beginning to grow. Some of these are invasive and some may be native, but they generally rise up a little sooner than grasses. If we burn them, we can maybe knock back those annual plants and favor grass growth,” says Schenck.
The purposes, he adds, are similar to why people apply herbicides to kill broadleaf plants to allow grass to grow – choosing a time when broadleaf plants are in an early emergent stage. Often crews are using fire to imitate what herbicide might do.
With spring burning, before everything really starts growing, the dry fuels may create enough heat to knock back early emerging annual plants and some of the woody invasive plants as well. “We’re hitting those woody plants before they start new growth,” he says.
Some fires are targeted for midyear. Warm-season burning or growing-season burning is gaining more interest. “In summer, we still have some old dead grass and dead annuals from the previous year, plus green vegetation. We may have higher humidity and temperatures.”
Keith Blair of Red Buffalo LLC is a Texas-certified burn manager/burn instructor who conducts prescribed burns on private rangeland and does prescribed burn workshops. He has been doing prescribed burns since the mid-1980s, gaining experience with the U.S. Fish and Wildlife Service and seeing differences between seasonal burns in the Dakotas and those in Texas.
With the heavy fuel loads now in many regions (and way behind, trying to reduce them), he realizes we don’t have time to restrain burns to a single season; it’s important to burn whatever we can in each season. “In general, at least here on the Southern Plains, winter and early spring burns tend to promote warm-season grasses,” he says. “In summer, results can be highly variable but may benefit forbs more than a winter burn does. With a decent summer burn, you can often do more damage to the brush [such as mesquite] or prickly pear that is encroaching on the grassland.”
Factors for a good burn
Heat, humidity and wind can all make a difference in how well a prescribed burn will work or how safe it will be. The biggest variable is fuel moisture and dryness. This is controlled by temperature and humidity in dead fuels and moisture in live fuels. Red Buffalo’s outfit has Ashe juniper and redberry juniper, and they monitor the live fuel moisture in those plants.
“If it’s at a high level, and we put fire into a thick stand of that juniper, it will do nothing. If moisture level is low in those plants, we can put a fire into those stands, and it will explode and burn very well,” Blair says.
Thus there are some limitations within prescriptions. “When doing the black lines, we want the moisture to be a little high – so the fire can be easily controlled – but when we do the head fire, we want fuel moisture low so we can kill more of those plants,” Blair explains.
“During growing season, we have a good chance to get fires going, and sometimes winds are not as strong,” says Schenck. “We can knock back invasive species quite well, for two reasons. The fire doesn’t move very fast through green vegetation and, by having a longer time burning against a mesquite bush or small cedar tree, there’s a better chance of affecting that bush or tree. To kill the plant, it doesn’t have to all burn up. All the fire needs to do is boil/damage the cambium layer around the surface and affect that plant’s circulatory system, and it dies,” he explains.
Summer fires tend to move more slowly through the green vegetation, which takes longer to fully ignite. Often, you get a more thorough kill on some of the invasive species because of this longer burning time.
There are some cautions, however, when doing summer growing-season burning.
“We’re always gambling on the weather and hope traditional moisture does come after the burn,” says Schenck. “Everything will grow back, but if there’s no moisture right away, it may not grow back soon enough for the following spring. There is always the possibility that if you hit it fairly hard and then have drought conditions, you risk potential erosion if the vegetation does not re-establish soon enough. We can’t control the weather, so we are gambling with the natural process.”
