Mastication is becoming a common fuel treatment method in forests and shrublands of the United States, especially where prescribed fire or mechanical fuel removal is difficult. Such sites are often located in the wildland urban interface (WUI) where fuel treatments must be carefully administered because of the risk to nearby communities. Mastication is used to grind the canopy and/or understory vegetation into small pieces, leave the particles on the ground, and reduce the chances of a fire spreading through the forest canopy. Once on the ground, fuels are either burned by prescribed fire or left to decompose.