How Thinning Impacts Fuels

A few years ago, the Custer Gallatin National Forest thinned the area on Kirk Hill by Bozeman to reduce fuels.

As has been reported, one of the problems with any fuel reduction is that the probably that a fire will encounter it during the period when it’s potentially effective is very small–usually around 1%.

A second problem is that thinning often increases the abundance of “fine fuels’ like grasses, shrubs and small trees. Large trees are less likely to burn which is why we get snags. So removal of larger trees does not necesssarily result in less fire spread.  It’s not the total biomass that determines fire spread, but the percentage of fine fuels like grasses.

Below is the Kirk Hill area immediately after thinning. Within two years, the area is now covered with dried grass–a highly flammable fuel. For the last picture I turned 180 degrees to photograph the same forest twenty feet from the previous photo but in forest that hasn’t been thinned. Note the fuel load is lower. The vegetation in the shade is still green–thus less flammable than the cured grass in the thinned area.





  1. Richard Halsey Avatar

    Simple, elegant, and extremely clear. Thanks, George. Unfortunately, the financial incentive to log and clear habitat supersedes science and logic… and the preservation of the natural world.

  2. Jerry Thiessen Avatar
    Jerry Thiessen

    Was the grass planted or natural? Was the grass native or alien? Grass fires in this ecological setting can yield far different results, even positive results, than cheat grass fires in sagebrush. We need to be clear about the message.

  3. Jeff Hoffman Avatar

    Here’s a more fundamental and better reason not to kill trees: It’s totally immoral to kill anything you don’t eat. Humans don’t eat trees, so they have no business killing them. PERIOD!!!

  4. Rose Herrmann Avatar
    Rose Herrmann

    There should also be wild horses put in forests as they act as a natural fire brigade so there is no need to clear cut and the predators (if they are not viciously murdered) will keep the population in check. I’m talking wolves , grizzly bears and mountain lions


George Wuerthner is an ecologist and writer who has published 38 books on various topics related to environmental and natural history. He has visited over 400 designated wilderness areas and over 200 national park units.

Subscribe to get new posts right in your Inbox

George Wuerthner