Duff, a layer of partially decayed organic material, is a normal part of the forest floor. However, when fire has been absent for too long, it can build up to levels that increase a number of risks associated with prescribed fire. Understanding what duff is, how it behaves, and how to incorporate it into your plans is important for any landowner looking to safely reintroduce fire into long-unburned land.

Duff is a layer of partially decaying organic material that has accumulated on the forest floor, just beneath the litter layer. While duff can look different depending on the ecosystem, duff is usually composed of bark, leaf litter, pine cones, roots, and woody fuels that have been slowly decomposing for months or years. Additionally, duff tends to build up most heavily around the base of trees. In forests that haven’t burned in a long time, this layer can grow quite thick and dense, creating “duff mounds” around the trunks of trees. To the touch, duff feels springy, cushion-like, or spongy, and walking on this layer can feel like sinking into a soft carpet.

Watch this Southern Fire Exchange Video on Duff:

Check out this Southern Fire Exchange fact sheet on Duff >

Without regular burning or removal, duff can accumulate to unnatural depths. Unlike the quick-burning litter layer, when ignited, duff tends to smolder, a slow combustion process that can continue long after visible flames of a prescribed fire have died down. This creates two major concerns:

1. Tree damage and delayed mortality
2. Extended smoke production and longer mop-up operations

These concerns emphasize why duff deserves special attention before you put fire on the ground.

Watch this Southern Fire Exchange video on Duff and Tree Mortality:

Reintroducing fire to duff-heavy forests reduces the volume of accumulated organic material, recycles nutrients into the soil, protects tree health, and helps restore the open understory that many ecosystems depend on. You just have to approach sites with heavy duff carefully and with plenty of patience. Remember: it took years to accumulate duff on a site, it will take years to safely reduce the duff load.

Watch this Southern Fire Exchange video on Duff and Reintroducing Fire:

With proper planning, you can safely reduce duff buildup and reintroduce prescribed fire into your forest. Remember these guiding steps:

1. Assess current duff moisture on your land through the Touch Test or by using a duff moisture meter. Be sure to assess the moisture content of all layers of duff.
2. Burn when duff is sufficiently moist (at least 1” of rain in last 24 hours or 3-4” inches of rain in last 48 hours)
3. Softly rake duff out from the base of trees
4. Assess trees of concern post-burn
5. Ensure complete mop-up of duff and duff mounds to prevent smoldering

This spring, the Southern Fire Exchange (SFE) and the Consortium of Appalachian Fire Managers and Scientists (CAFMS) teamed up to lead two innovative duff fire science and management workshops in North Carolina: one in the mountain region and one in the sandhills region of the state. Collectively, the workshops brought together 78 natural resource managers and researchers from across the Southeast to learn about duff fire science and management. Participants gained a greater understanding of what duff is, its relationship to fire exclusion, the fundamental challenges it presents to land management, and how to plan prescribed fires in areas with heavy duff loads.

Both workshops featured indoor presentations, group discussions, and outdoor field trips to sites where duff-related challenges were present. During the “Duff in the Mountains” workshop field trip to the Green River Game Lands, participants were able to see and feel duff firsthand and observe the results of treatments tested in long-term fire management research plots. During the “Duff in the Sandhills” workshop field trip at Weymouth Woods, participants had the opportunity to observe duff actively burning following a prescribed fire.

The active participation and insightful questions from attendees created highly collaborative learning experiences. The group’s positive energy and engagement underscored the need for continued duff fire science research and future workshops in additional locations facing similar challenges.

The Duff in the Mountains Fire Science Workshop was held at the Henderson County Cooperative Extension Center and the Green River Game Lands, while the Duff in the Sandhills Fire Science Workshop was held at Weymouth Woods Sandhills Nature Preserve. Funding to support the workshops was provided by the Joint Fire Science Program, the Triangle Land Conservancy, and the Foothills Conservancy of North Carolina.

SFE is led by staff from the University of Florida IFAS School of Forest, Fisheries, and Geomatic Sciences; North Carolina State University Forestry Extension; and Tall Timbers. CAFMS is led by staff from the Virginia Tech Department of Forest Resources and Environmental Conservation and the Clemson University Department of Forestry and Environmental Conservation.