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Summer Grazing Deferment for Prescribed Burns

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Late winter-spring burns are probably the farthest thing from your mind in the middle of the summer, but planning for an adequate fuel load is necessary if future prescribed burns are to accomplish your goals. Most rangeland burns rely on fine fuel made up predominantly of warm-season grasses for combustion to create the desired impacts. As such, adequate "standing dead" grasses must remain in the field to serve as fine fuel until the time of a prescribed fire.

So what is an adequate fuel load? The answer depends on the goal(s) set for a prescribed fire, but generally ranges between 1,000 and 4,000 pounds of dry matter per acre (see examples). Fuel loads greater than 2,000 pounds per acre are usually required for successful "brush control" fires, while fuel loads near the lower end often result in very patchy burns. Environmental factors such as wind speed, relative humidity and air temperature also factor into the fire's behavior and the performance of any given burn.

Many prescribed burns require season-long grazing deferment for adequate fine fuel production and accumulation. However, with adequate precipitation, some early grazing can be allowed on productive sites. If an area to be burned is grazed, it is important to remember that most native warm-season grasses in the Southern Great Plains generally produce 75 percent of their biomass by mid-July. Of course, the actual growth curve varies from year to year with precipitation amount and timing.

Much of the warm-season forage or fine fuel removed through grazing after this time likely will not be replaced by additional growth. Therefore, to ensure adequate fuel loads for an upcoming winter-spring burn, most pastures in a planned burn area should be deferred from grazing after mid-July. Pastures that are grazed after this period should be monitored very closely to prevent removal of too much fine fuel.

different fuel loadsThe photos show examples of different fuel loads. Photo A shows a pasture with 600 pounds of dry matter per acre.

dry matterThe pasture in Photo B has 1,400 pounds of dry matter per acre - within the 1,000 to 4,000 pounds per acre range that is generally desired.

Summer Grazing DefermentPhoto C shows a field with 2,400 pounds per acre of dry matter. Brush control burns usually require more than 2,000 pounds of dry matter per acre.

Ken Gee
Retired Wildlife Research Specialist