Loggers of public lands and their allies are increasingly using 'forest health' arguments to promote more logging, especially in the last unlogged, unroaded reaches of our national forest system. According to this view, there are too many trees in the woods. Being flammable, they will make forest fires burn superhot and cause unnaturally great damage. Solution: cut lots of the trees down. At the heart of the many defects in this theory are three hard facts. One: 'forest health' logging to reduce fire risk is a giant, untested experiment. Two: logging, even 'forest health' logging, causes ecological problems and can actually promote fires. And three: unmanaged, unroaded forests are generally those in the best ecological shape.

No broad scale, systematic, scientific study has ever shown that any kind of logging reduces a forest's overall susceptibility to fire. There are a few, small scale and preliminary studies, and a wealth of anecdotal evidence about the linkage between thinning forests and subsequent fire. They present a conflicted picture, with the scientific work tending to indicate increased fire susceptibility in the wake of all forms of logging, as actually done in the field by logging crews. The timber industry can take visitors to sites where fire hit a thinned stand and decreased in intensity. Similarly, environmentalists can take them to any number of counterexamples, where a cool burning, non-lethal fire hit a thinned stand and blew up into a serious conflagration.

There are multiple reasons why even 'forest health' logging can increase a forest's susceptibility to fire. First, it is the little trees and saplings that are most flammable, but loggers only want medium and large size trees, which have thicker, more fire-resistant bark and have often survived previous fires. Second, it is difficult and expensive to log without creating highly flammable 'slash' from the limbs and needles of logged trees. Third, logging opens up forest stands to the drying effects of wind and sun, which increases their flammability; undisturbed forests, by contrast often have cooler, moister microclimate conditions under the forest canopy. Fourth, logging stresses forest ecosystems in a variety of ways, including damage to residual trees, compaction of soils so they don't absorb water well or allow proper root growth, and spread of diseases and invasive alien plants into the forest interior. Fifth, logging disrupts natural processes that modulate ecosystem health, for example by eliminating the dead trees that house insects and birds which control forest pests, and by driving out forest interior animal species like tree voles that play a keystone role in trees' nutrient cycling. Sixth, logging equipment, loggers themselves, and others who use logging roads are all frequent sources of fire starts, through sparks, cigarettes, escaped slash fires, campfires, unmuffled exhausts, and so forth.