New Study Indicates Restoration of Unlogged Fire-excluded Forests Requires a Light Touch

While it is well known that fire suppression has resulted in structural changes in the dry interior forests of the western U.S., previous studies that have attempted to evaluate the changes in stand structure as a result of fire suppression have failed to consider how commercial logging that predated the fire suppression had already impacted the forest structure. For example, in the Blue Mountains of Oregon, commercial logging began in the 1870s, predating the effective fire suppression period by more than 50 years. This question is very important because the distinct forest management histories in previously logged vs. unlogged stands may necessitate unique restoration approaches. A new study in press with Ecological Applications entitled “Interactive effects of historical logging and fire exclusion on contemporary structure of ponderosa pine/Douglas-fir forests of the Northern Rockies,” has specifically addressed this critical question.

The Naficy et al (2010) study encompasses a broad geographic region within the northern Rockies, extending from central Montana to the Payette National Forest of western Idaho. The study is based on an extensive field campaign that identified paired logged and unlogged ponderosa pine/ Douglas-fir, fire-excluded forests. Notwithstanding the logging history, the paired logged and unlogged sites have similar management histories including effective fire suppression and similar physiographic characteristics allowing for comparison of stand structural differences that can be attributed to the logging.

Naficy et al. (2010) found that:
- Average total stand density of logged sites was more than twice that of unlogged sites.
- While the total Basal Area was similar between logged and unlogged sites, in unlogged sites the Basal Area was more concentrated in larger diameter Ponderosa Pine trees.
- In previously logged stands, the lack of large trees and abundance of smaller trees resulted in strong dominance of small fire-intolerant trees.
- Unlogged stands showed a more even distribution of ponderosa pine tree density across all size classes.

Naficy et al. (2010) shows that historically logged, fire-excluded ponderosa pine forests of the Northern Rocky Mountains have more homogenous stand structure, much higher average stand density, more standing dead trees and greater numbers and dominance of small, fire-intolerant trees than their unlogged, fire excluded counterparts, making them more prone to severe, stand-replacing wildfires than unlogged, fire excluded stands. While previously logged fire excluded forests may benefit from significant mechanical stand manipulations before fire can be safely introduced, unlogged, fire-excluded forests may require much less invasive treatments. Naficy et al. (2010) discusses the potential long-term risks associated with mechanical treatments, especially in previously unlogged forests. While acknowledging the differences between historical logging and contemporary fuels reduction practices, Naficy et al (2010) also recognizes the similarities; soil disturbance and reduction of canopy cover. Furthermore the reality of modern fuel reduction methods targeting medium and large overstory trees in order to increase canopy spacing and reduce crown fire spread and to help offset treatment costs (see photo).

Naficy et al (2010) concludes “Clearly, there is a need for careful consideration of the long-term effects of modern silvicultural treatments as part of a forward-looking fuels management approach that balances fire hazard reduction with wildlife habitat needs and other ecological values and is commensurate with the realistic financial and institutional ability of public land management agencies to maintain such treatments over time.”

A large Ponderosa Pine (marked in blue), growing here for well over a century is marked for cut in the Sugar Timber Sale. HCPC has worked diligently to explain to the Forest Service why restoration of fire-adapted old growth stands should not involved cutting early successional species that are older than the historical fire suppression period.

David Mildrexler,
Ecosystem Conservation Coordinator, and
Staff Scientist