Okanogan-Wenatchee National Forest - Mastication Study

Mastication Study

Funded by the Joint Fire Sciences Program

Effects of mechanically generated slash particle size on prescribed fire behavior and subsequent vegetation effects

In the fire prone ecosystems of the interior Northwest, resource managers have begun to reduce fuel loadings by manipulating forest structure to achieve natural, pre-settlement conditions. This will facilitate a return to normal fire intervals and help reduce the potential of large catastrophic wildfires.

In order to restore pre-settlement forest structure, foresters are having to correct fire exclusion, resource extraction, and extensive grazing that have occurred in the 20th century. There are many options and tools at their disposal, and guidance is needed on what tools work best.

mastication head

Mastication head mounted to excavator

One of the tools for accomplishing this is mastication of non-merchantable trees. This proposed study is designed to assess mechanical fuels treatment of non-merchantable trees with mastication equipment. Its goal is to quantify the relationship between mastication effect, different particle size resulting from the mastication effort, fire behavior, fire effects, soil effects, and vegetation response. Particular attention will be paid to determining optimal particle size for the desired effect. The results of this study will provide managers with guidelines to develop thinning prescriptions using mastication and subsequent prescribed fire.

Several objectives will be examined in this project:

1. How does slash particle size and fuel bed depth affect fire intensity and severity?

2. How do different mastication efforts and subsequent prescribed fire affect understory and overstory vegetation?

3. What are the effects of soil heating from burning different types of slash on the soil nutrients?

4. What are the effects to soil when slash is not burned?

thinned forest

This stand of trees has been pre-commercially thinned by mechanical mastication



All units will receive the same thinning prescription. Slash particle mastication effort will result in three size particles from three effort intensities: small particles, from intense mastication effort; mixed piece sizes, from medium effort, and large pieces from low intensity effort. All burn units will then receive the same prescribed fire prescription. Each treatment, including the controls, will be repeated three times; the controls will lie outside the burn units.

masticated fuel

Masticated fuel (fine)



Completion Date
Meet with hosting District to discuss research plans
February 2004
Develop silvicultural and burning prescriptions with hosting District
April 2005
Lay out experimental units
May 2005
Collect pre-treatment data
August 2005
Complete mastication thinning
July 2007
Collect field data on thinned plots
September 2007
Prescribed burn selected units
October 2007
Collect field data on thinned and burned plots
November 2007
Finalize entry of field data and analyze results
January 2008
Submit final report and publications
February 2008

Hosting agencies

Joint Fire Sciences Program

US Forest Service, Okanogan-Wenatchee NF, Wenatchee, WA

US Forest Service, PNW Research Station, Wenatchee, WA