For several years, members of the Mountain Area Safety Taskforce have been working with the U.S. Forest Service’s Pacific Southwest Research to evaluate whether fuels treatments that leave chipped woody material behind are contributing to fire abatement or creating a fire problem.
The lead investigator, Dr. Pamela E. Padgett, research plant physiologist at the research center, reported on the progress of the research at the Dec. 17 MAST meeting. She described the research as looking at whether “we were altering a vertical fuels problem into a horizontal problem.”
Several preliminary insights have been observed and Padgett is planning to obtain peer review of the work in order to publish it in 2015. First, the team found that the finer the wood is chipped the less flammable it is. The fine chips compact and compress more easily, thus reducing the amount of oxygen to the fuel below the ground surface. The more compact the fuel bed becomes, the less ignitable. Fine chips are considered less than an inch on the longest axis. The chips tend to be rectangular, with one axis much longer than the other, Padgett said to clarify.
Also, the fresher the fuel, the more volatile compounds that remain. These tend to be more ignitable and able to carry fire. However, composting the chips reduces volatile compounds and their fire capacity.
Not surprisingly, the softwoods, such as pine, were found to be more flammable than hardwoods, such as manzanita and oak. However, in the laboratory, freshly chipped oak was found to have a very fast rate of fire spread compared to other wood chips.
Finally, the depth of the chips was also an important contributor to their capacity to burn and carry the fire. Fuel beds less than 5 inches deep “exhibited very little ignition or very little spread,” Padgett said. The shallow beds were much less vulnerable than fuel beds 10 inches or more in depth. At these depths, the nature of the wood was almost irrelevant.
Work on the project started in 2010. Besides laboratory tests of chips, the final portion was a field test in the Poppet Flats fuelbreak area.
Padgett indicated that next year the brochures for the public will be prepared in addition to the professional publication of the results. The brochures will advise the public as to the best type of chipping for woody material.