Analysis Shows Thinned Forests Were No Match for Last Year's Mega-Fire in Calif.

Sometimes even the best efforts to return a forest to a less fire-prone state go up in flames.

This proved to be the case when the Rim fire created an inferno in California's Yosemite National Park last year.  A recently published analysis of Yosemite land burned during the record-breaking wildfire demonstrates that when blazes become extreme -- so large and hot that they create their own independent weather patterns -- they can easily destroy forests that have been restored, or thinned of underbrush, through recent controlled burns.

The U.S. Forest Service has long argued that management techniques like the removal of "fuel," such as brush and deadwood, by using controlled burns can significantly diminish extreme fire activity and protect forest habitats.

For example fire crews noted that a recent blaze in Arizona's Apache-Sitgreaves National Forests was made significantly easier to control thanks to a tree-thinning project there. Not only that, but larger trees within the treated areas proved resilient to the flames and many appeared to have survived the incident.

But by examining forest plots where Yosemite had allowed smaller fires to burn and consume fuels within the last 14 years -- a fire regime similar to what the forest experienced before the early 1900s -- researchers behind the new study show that when the Rim fire was at its most severe, the vast majority of trees in these restored plots were still killed.  The research appears in the journal Forest Ecology and Management.

The researchers stressed that the Rim fire did not start within Yosemite's restored forests but on adjacent national forest property, and that its rapid spread was in large part due to decades of fire suppression and fuel buildup outside the national park.

"We basically have artificially constrained fires to burn under very, very extreme conditions, and under those extreme conditions, fires generally will be able to overwhelm restoration efforts," said study co-author Brandon Collins, a researcher with the USDA Forest Service's Pacific Southwest Research Station in Davis, Calif.

"To me what it spells out is that we need to be doing fuel reduction efforts at much larger scales than we currently are," Collins added.  "We shouldn't be relying on parks to continue their burning programs -- it means we have a bigger problem on the landscape."

Analysis Shows Thinned Forests Were No Match for Last Year's Mega-Fire in Calif.