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Earth Notes: After a Fire, Chain Saws?

Each summer, wildfire scorches western forests, leaving millions of charred trees in its wake. Often logging trucks are not far behind, moving in to harvest the dead trees.

While salvage logging can help recoup economic value from dead trees, the practice exacts an ecological cost. Even in fire-adapted forests, like the ponderosa pine forests here in the Southwest, high-intensity fire usually increases soil erosion by burning off ground cover and reducing the soil’s capacity to absorb water.

Salvage logging further disturbs the soil, with varied effects. Heavy logging equipment breaks up the water-repellent soil layer formed by fire. That could potentially decrease runoff. But it also causes extensive soil compaction and disturbance, which increases erosion.

A recent study helped quantify the cumulative impacts of salvage logging. Observing both logged and unlogged burned forests for nine years, Joseph Wagenbrenner of Michigan Technological University and his research team found 10 to 100 times more stream sedimentation in salvage-logged sites, along with reduced rates of vegetation regrowth.

They also found that certain management practices, like leaving plenty of woody debris behind, decrease the severity of soil erosion on logged sites. As a result, the team recommended several additional soil conservation practices for landowners who opt to salvage log, including building water diversions and logging when the ground is frozen.

Climate models predict increasingly frequent and severe wildfires in the Southwest. Developing sound conservation practices with which to respond to these wildfires is an essential part of maintaining forest resilience in the face of climate change.

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