Wildfire Corner: Benefits of Forest Mastication

By Guy Gifford, Landowner Assistance Forester and Fire Prevention and Firewise Coordinator, Washington State Department of Natural Resources, Northeast Region, guy.gifford@dnr.wa.gov

In the past several years, there has been increased awareness of the role that brush and dense stands of trees play in spreading fire, which has driven the effort to reduce fuels around homes – particularly those in the wildland urban/forest interface. This has put pressure on forest landowners to remove trees and brushy vegetation from their properties, but they may not have experience with the best methods of doing this. Forest mastication, or “forest mulching,” is a common method that achieves results.

Forest mastication is a mechanical treatment that changes how forest vegetation burns during a wildfire. It rearranges the vegetation by chopping it into smaller pieces and spreading it out over the ground.

Instead of having tall shrubs or young trees with their canopy touching, you “chew” them up and spread them out on the forest floor. This reduces the wildfire flame length when it burns through your property. Shorter flame lengths are easier to put out than tall flame lengths and pose less of a risk of turning into a crown fire.

Contractors use several different types of masticators. (The term masticator refers to the head on the machine, not the actual machine that drives around in the woods.) The most common one used on private property in Washington is a horizontal drum masticator. Less common types include rotary disk masticators and excavator-mounted masticators.

There are several different types of masticators. From left to right: rotary mastication head (Photo: FMI Equipment), rotary disk masticator (Photo: Advanced Forest), and a mini excavator with a masticator head (Photo: ASV-Australia).

Landowners frequently want to know what their land will look like after a masticator’s work is done, and rightfully so.

The short answer is that it will look a lot different. Mastication disturbs a lot more vegetation than cutting by hand, leaving behind a highly disturbed appearance. Typically, any place the masticator moves over will result in vegetation being masticated.

However, this highly disturbed look does not last very long! By the following June, the evidence of this destruction will fade away. First, the “white” pieces of freshly cut wood will turn a grayish color due to the natural weathering process and blend in with all the other woody debris on the forest floor. Then needles and leaves from the remaining trees and shrubs will fall, covering some of the debris and disturbed soil. Finally, new plant growth will flourish and hide much of the masticated material.

Landowners also frequently ask about how big the pieces of debris will be after mastication is complete. This can be influenced by the operator and their rate of travel over the forest floor; the slower they go, the smaller the pieces will be.

This mastication was done faster and left large-diameter material, including some large downed logs (Photo: Chris Schnepf, University of Idaho)

The size of the remaining debris is something you should discuss with your contractor. What you decide you want as a landowner will depend on your objectives and preferences. Fine debris decay much faster than large pieces. However, leaving large-diameter materials and large intact downed logs can be beneficial. The term foresters and wildlife biologists use for these large logs is coarse woody debris.  Large coarse woody debris provides habitat for insects and even small mammals while building organic matter in the soil over a longer period.

Mastication is a vital and efficient tool for landowners looking to reduce the risk of wildfire to their homes. Though the area will look highly disturbed at first, this is only a short-term nuisance. Long-term, mastication can provide wildlife habitat (if you choose) and, most importantly, some peace of mind during fire season.

To watch a masticator in action and learn more about the process and benefits, check out the videos below, and the recent U.S. Forest Service publication “To Masticate or Not.”

Forestry Mulching 101 – CELM Bigfork Montana

Bobcat Forestry Cutter Attachment – Bobcat Manufacturing

Mastication Treatments in Southwestern Forests – Southwest Fire Science Consortium

To Masticate or Not – U.S. Forest Service Publication