Alaska's fuel breaks, twenty years on: spruce, birch and thaw

A black spruce forest burning. Alaska Climate Adaptation Science Center.

Interior Alaska is covered in black spruce, one of the most flammable forests on Earth, and as the climate warms and dries it burns more often. To protect towns, crews cut fuel breaks: they thin the spruce by hand, or scrape the ground bare with a bulldozer's blade — "shearblading". A study that went back to such breaks about twenty years later found that the two methods send the forest down very different paths, and that neither reliably tames a fire.

What the researchers did

They re-measured a network of fuel breaks in Interior Alaska, some thinned by hand and some shearbladed, about two decades after treatment. At each they recorded which trees were coming back, what grew beneath them, and how deep the ground thawed above the permafrost each summer. They also modelled how fast a surface fire would spread through each, how long its flames would be, and how intense it would burn, compared with untreated spruce.

What they found

What it means

• Shearblading has lasting side effects. It turns spruce to birch and aspen — which burn less readily — but it also degrades the permafrost beneath.
• Thinning is gentler on the ground, but the spruce comes back.
• Neither consistently reduced fire behaviour compared with an untreated stand. How well a break works depends on how untreated spruce is modelled — and the standard fuel models do not capture how these stands change as they regrow.
• Fire managers need better data: fuel descriptions and models that follow the vegetation as it changes year to year.

Sources

Written from "Boreal forest ecology and wildland fire fuel treatments", National Park Service, summarising M. A. Boyd, X. J. Walker, J. Barnes and others (2023), a study of fuel treatments in Interior Alaska co-authored by Park Service fire ecologist Jennifer Barnes.