Experiments provide science for prescribed burns

Rogers said timing and weather conditions are very important, but fuel loads are also an important component to produce enough fire energy to kill woody plants. This will likely require land managers to restrict access by grazing animals to allow vegetation to grow and provide adequate vegetative fuel for the burn to reach higher energy levels.

His team set up 72 randomized 30 foot by 30 foot experimental plots at the Sonora station to identify various ranges of fuel and fire energy. Researchers restricted livestock, including goats, sheep and cattle, from grazing access ranging from zero, limited and full access.

Rogers noted factors that affected fuel loads within the experimental plots. For example, researchers were unable to completely restrict axis deer, which are invasive grazers, from the plots. He also noted how grass productivity factored into fuel buildup, whether from lack of soil moisture or in areas with rocky and/or marginal soils.

Researchers added fuel like hay and dried juniper in measured amounts to randomized plots before burns to simulate higher fuel loads than could be achieved before the experiment. The team used video and infrared video cameras stationed 40 feet in the air via a boom lift to capture each burn. Other instrumentation above and below ground was used to collect temperatures created by the fire.

“The infrared camera and instrumentation allowed us to track heat signatures and the fire’s energy throughout each burn, and that gave us a better understanding of the relationship between fuel loads, weather conditions and fire energy,” Rogers said. “We want to eventually be able to give a land manager our best recommendations to make prescribed fire most effective as a tool to control woody plants.”

Prescribed burns as a tool

There were other claims about prescribed fire that Rogers’ study also dispelled. While high-energy fires will kill woody plants, it does not negatively impact soils or native plants in these vegetative communities, including seed grasses.

The study showed high-energy fires did not “sterilize the soil” or seal the soil like clay in a kiln, he said. High-energy fires also did not disrupt soil microbiome communities or native plant recovery.

High-energy fires did not decrease the base plant community dynamics, he said. For instance, “bud banks” of grasses bounced back even better after the burn, and succulents like Bacchus recovered with no long-term negative impacts.

Rogers said he is focused on providing science-based solutions for landowners and land managers. He believes the study answered several foundational questions related to the efficacy and impact of prescribed burns.

“Science is showing that prescribed burns can be an important and beneficial tool for controlling invasive woody plants, improving ag production potential for farmers and ranchers and habitat for wildlife while also reducing fuel loads that could lead to catastrophic wildfires,” he said. “We hope this study can be part of that conversation.”