U.S. Joint Fire Science Program


Date of this Version


Document Type



Fire Science Brief, Issue 70, September 2009


US government work.


Mastication, the mechanical shredding and chipping of small trees and shrubs, has been rapidly embraced by land managers as a treatment to reduce the risk of wildfire in the wildland/urban interface and to provide fire breaks in more remote areas. In the western United States, the use of mastication has more than doubled in the past 5 to 10 years, but until recently little was known about the novel characteristics of this artificial fuelbed or how it might behave when confronted with fi re. Mastication does not reduce the total amount of fuel; it essentially takes ladder fuels—live and dead shrubs and small trees—and redistributes them to the forest floor. This thick mat may temporarily suppress growth of new vegetation and hold in soil and fuel moisture. Recent research conducted at 10 sites in southern Oregon and northern California, across a range of forest types and fuel loads, has begun to characterize masticated fuelbeds, determine the potential effects of particle size and moisture on fire behavior, assess the heating potential on soils and possible damage to soil organisms and trees, and determine whether current models for predicting fire behavior of natural fuels will be valid in estimating fire’s effects in masticated fuelbeds. Research on the early response of understory and midstory vegetation to mastication and subsequent alternative treatments is also helping determine whether future treatments will be required to discourage regeneration.