Forestry
9:03 am
Mon March 18, 2013

Logging Leftovers Could Keep Invasive Species Out

Credit USDA

A new study from the research arm of the Forest Service suggests that leaving behind broken branches and the tips of treetops after logging can help fight invasive species.

Scientists suspected that fir boughs and other logging leftovers could act like gardener’s mulch and protect the soil.

Tim Harrington is with the Pacific Northwest Research Station. He’s part of a group that looks at the long term effects of logging. Harrington set up an experiment growing Doug fir seedlings under different amounts of cover. He found that young firs grew best when about half of the soil was covered with old branches.

“It’s kind of like a no-till system," he says. "Basically, do not the disturb the soil any more than you have to, and you will benefit the native vegetation. And you’ll also retain growing space for the seedlings of conifers that we’re trying to grow.”

Harrington says the woody cap over the soil helped trap plant nutrients like carbon and nitrogen.
And it protected the site from invasive species that often blow in on the wind and take over clear-cuts.

“Scotch broom, we found early in the study, that it was inhibited," he says. "Hairy cats ear, which is actually like a dandelion species, they’re just not coming in because they don’t have the exposed mineral soil to colonize.”

So, could leaving behind slash help provide an alternative to spraying herbicides on clear-cuts to control weeds? That depends a little on your perspective.

“I think the slash retention is potentially a helpful thing," says Scott Holub, a research scientist with Weyerhaeuser.

He says Harrington’s results showed that the native firs grew the most when slash and herbicides were used together to knock back weeds.

“Really the big driver we find is the weeds and when there’s more weeds there’s less tree growth,” Holub says.

Holob says Weyerhaeuser is conducting its own experiments to figure out whether leaving behind branches and needles after logging will keep the soil healthier in the long run.

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