Metlen, Kerry.  2002.  Undergrowth vegetation response to fuel reduction treatments in the Blue Mountains of eastern Oregon.  M.S. Thesis.  University of Montana.  74 pages.

Mechanical thinning and prescribed burning are two tools used by forest managers to reduce fire hazard in forest stands overstocked by decades of fire exclusion.  Thinning and burning often have dramatic impacts on the diversity, distribution, cover, and species composition of the undergrowth.

The mechanical treatment in this study was a thin-from-below utilizing a singlegrip harvester.  All trees greater than 32 cm at breast height were retained and slash was left in place to be trampled by the forwarder.  Prescribed burning occurred in the fall, consistent with the end of the historic fire season.  Burns were light in intensity and fairly uniform.

The Thin-and-Burn treatment was a combination of these two prescriptions.  Treatments tended to be more intense due to harvest generated fuels and subsequent overstory mortality.

This study evaluated the response of undergrowth vegetation to fuel reduction treatments in Douglas-fir/ponderosa pine forests at the Hungry Bob Fire/Fire Surrogate site in northeast Oregon one growing season after burning and three growing seasons after thinning.

• The Thin-only treatment did not affect species diversity.  Cover of grasses and shrubs increased and fire-sensitive species increased in frequency.
• Burn-only treatments reduced the diversity of the undergrowth.  Cover of grasses and shrubs were reduced and the frequency of fire adapted undergrowth species increased.

• Thin-and-Burn treatments responded in a fashion similar to the Burn-only, though with some reduction in the frequency of fire-sensitive species.
• Fuel reduction treatments did not strongly influence the undergrowth vegetation in this short-term study.  This could be due to the intensity of treatments, response time, disturbance history, and evolutionary background of these undergrowth communities.