Rangeland Resilience After Fire: Range Plant Ecosystems Able to Rebound

Ranchers affected by recent fires in South Dakota and surrounding states may have more questions than answers about how long they should wait before grazing pastures again. Long standing protocols suggest two growing seasons, but is that sufficient with current drought concerns? What plant health parameters should producers be looking for to make the best management decisions during the upcoming grazing season?

While pastures look particularly bleak in the aftermath of the recent Windy Fire in Adams County, North Dakota and Perkins County, South Dakota, the good news is that rangeland plants are highly resilient after a fire.

South Dakota State University Extension Rangeland Management Specialist Alexander Smart says that the bottom line from a range plant perspective is that a fire does not harm the plant itself.

“Grassland fires generally move over individual plants very rapidly, minimizing the duration and intensity of elevated temperatures,” he said. “The rate of post-fire recovery is controlled primarily by the condition of the vegetation before the fire and moisture conditions following the burn. Healthy, vigorous rangeland will recover rapidly following a fire.”

Lance Vermeire, USDA-ARS Rangeland Ecologist with the Fort Keogh Livestock and Range Research Laboratory at Miles City, Montana concurred.

“People often worry about plant vigor being harmed by fire, but that is not the case,” Vermeire said. “In addition to improved production, we observe increased forage quality and stimulation of the bud bank. The bud bank refers to buds below ground or in the crowns of plants that are the source of new stems. This is very important because in the Great Plains greater than 99% of the tillers (stems) produced by our perennial plants originate from buds, not seed. It is sometimes suggested that grazing after fire be delayed until plants produce seed to help recovery. Given that our perennial plants do not rely on seed for production and tend to respond favorably to fire, such a delay is not that helpful. Monitoring of plant health after fire is really no different than what should normally be done in making management decisions when fire has not occurred.”

What takes longest to rebuild is the layer of litter that helps to cover the soil below the plant understory.

“There’s an entire ecosystem below the grass stand,” Smart said. “The litter layer plays a valuable part in how that ecosystem works. It feeds the worms and the beneficial bacteria in the soil. It helps to protect the soil from wind and water erosion and helps to lock in soil moisture. The litter is also part of the habitat for the birds and small mammals that make their homes on the range. It may take one to two years to get back to a normal equilibrium between standing grass cover and the layer of litter on the soil surface.”

Data on winter fires is very limited for the northern Great Plains. Typically, snow cover and colder temperatures inhibit wildfires during the winter season. Most prescribed burns used to study range plants’ response to fire are planned in spring or fall, but Lance Vermeire was able to provide some research results specific to a dormant season fire.

“We burned during December 2003 and that was followed by severe drought in 2004,” Vermeire said. “Fire increased production considerably compared to non-burned plots that were grazed or not grazed. Soil water content was slightly less on burned sites than non-burned sites, but that could have been driven completely by the extra production and plants using more water. We have generally shown burned sites to be slightly drier or the same as non-burned. People often worry that fire dries soil out because the loss of litter cover exposes soil to more evaporation. There is a trade-off though because much of our rain comes in small events, and litter can intercept much or all of it so some of that rain never reaches the soil. Ultimately, we are interested in plant production and fire has consistently had neutral to positive effects on plant production.”

Fire is not a newcomer to the rangeland ecosystems of the northern Great Plains.

“When the buffalo were here, of course they would graze areas that had been burned,” Smart said. “Then they would move on to a different area and the plants were able to regrow.”

Controlled burns are often prescribed as a management tool to help decrease less desirable forages and increase more desirable plants. Wildfires have the same effect. While pounds of forage produced per acre may increase, stay the same or decrease after a fire depending on subsequent moisture received and whether the rangeland in question is predominately tall grass, mixed grass or short grass prairie, in the long run a fire can be beneficial to both the plant community and the producer.

“In our area, the species that tend to be harmed by fire are weedy annuals and those that tend to benefit are preferred perennials,” Vermeire said. “Even when there is not an increase in total production, fire shifts the community to greater production of native perennial species that are preferred forages.”

Smart said that bunch grasses such as needle and thread grass and little bluestem, with the crown on the soil surface, will be key indicators of recovery after a fire.

“Get on the fire line and compare plants of the same species on either side,” he said. “Are the plants on the burned area shorter? Do they have fewer tillers? In hayfields, check the alfalfa, which might get damaged because it has its crown at the soil surface or slightly elevated. Rhizomatous grasses that tiller below the soil, like western wheatgrass or smooth brome will not be hurt.”

Cattle are no dummies when it comes to finding the best food and will obviously seek out areas of new growth after a fire. While the buffalo would eventually move on, cattle in a fenced pasture will come back repeatedly, favoring the fresh green areas untainted by a stand of old growth.

“We have seen rangelands have similar or greater production after fire,” Vermeire said. “We have also seen that plants are not sensitive to moderate grazing after fire; grazing can be safely resumed as soon as there is sufficient forage to be grazed. The limitation is that without the old forage, ranchers should wait until there is sufficient growth to support their herd and make sure that plant growth is keeping up with demand.”

This could mean delaying grazing until later in the season and/or reducing the time spent grazing affected pastures. Temporary fencing can be a simple solution to keep cattle from camping out on burned areas in a pasture and putting too much grazing pressure on the plants too soon and too frequently in situations where fire passed through one part of a pasture.

“Given free choice, animals will focus on recently burned sites,” Vermeire said.  I suspect that some of the belief that grazing after fire is damaging has come from situations where only a portion of the pasture burned.  In tallgrass prairie, people sometimes burn portions of pastures and purposely let animals heavily utilize those patches to increase plant diversity.  If a person has a pasture where only a portion was burned and they are concerned about that selective use, options for using that pasture include: 1) temporary fencing to separate burned and nonburned; 2) basing utilization strictly off of use of the burned area; 3) grazing later in the growing season or during fall when the contrast between burned and nonburned is not as great.”

Will looming drought complicate rangeland fire recovery?

Alexander Smart shared data gathered in 2006 at the South Dakota Grassland Coalition managed intensive grazing demonstration site following a September 2005 wildfire.

“Regrowth was significantly lower early in the season, but both burned and unburned areas had similar green biomass at the June sampling date,” he said. “At the July sampling date the burned area had 20% less green biomass compared to the unburned area. Averaged over the summer, the burned areas had 25% less green biomass compared to the unburned areas. These data indicate that wildfire reduces forage production the following year, especially in a dry year like 2006 (April-May precipitation was 59% below normal). The protective litter was 6 times greater in the unburned site, however this did not translate into drastic temperature differences between the burned and unburned areas as expected. The dry and hot summer may have minimized any protective advantage the abundant litter in the unburned area could have provided.”

Lance Vermeire says that while weather has the biggest single effect on production in rangelands for our region, interestingly, fire effects do not really vary with weather conditions.

“From a livestock production standpoint the major effect that drought would have after fire is that most or all of the old standing forage would have been consumed by fire, so ranchers are completely dependent on what is produced that year,” he said. “That effect is usually greatest during early spring because the old forage is gone and new production is limited early on. That effect is also limited because the old forage typically decomposes quickly during spring and much of it would be “lost” anyway. Our years of fire research have covered all conditions including record dry and wet periods. If it is very dry, production is low and if it is wet production is greater. However, the differences between burned and non-burned sites are similar across those weather conditions. Our grasslands are very resilient after fire.”