Machine being tested could replace slash fires

By Bebe Crouse

The Nature Convervancy

You may have seen a strange piece of machinery being towed through the area recently. It looks like a rail car-size dumpster mounted on tank treads. It's called a Tigercat Carbonator. It has nothing to do with producing fizzy beverages, but it will turn the woody slash piles left after forest thinning into a charcoal-like amendment that helps soil hold onto moisture and nutrients.

The Nature Conservancy, public agencies and private landowners have experimented with producing small amounts of biochar, but we wanted to find a way to take the process to a larger scale. So, in partnership with Blackfoot Challenge, U.S. Bureau of Land Management, University of Montana, U.S. Forest Service and private land owners we got a chance to go a lot bigger.

In October, a trained crew brought the Carbonator out from Oregon and, as a demonstration project, started processing the slash piles that had accumulated during thinning on land owned by TNC land and the BLM in the Lower Gold Creek-Twin Creek area. We're pretty excited about early trials.

If you've spent any time living around forests, you've probably seen the plumes of smoke that rises up from the woods during burn season. Because there is not a market for the small trees that are removed during thinning, they have traditionally been heaped into big piles and torched.

The process can produce a lot of smoke, especially if the trees are still pretty green, not so with the Carbonator.

With the Carbonator, the woody material is loaded into its big burn box and ignited. The machine uses fans to stoke the fire until it reaches very high temperatures, which can happen relatively quickly. Once heated, more material is fed into the burn box. Because the smoke produced is blown back into the system by the fans, very little of it goes into the air, except for what is produced when the material is initially ignited. The smoke produced is a small fraction of what would have been created by burning the slash in the open.

Once the material burns down to smaller chunks, it drops through a grate at the bottom of the burn box and is quenched in a water bath. Then the charred material is extruded by several big augers into a pile. At that point it is cool to the touch and ready to be hauled to local ranches to use on their hayfields. Another exciting characteristic of biochar is that it is a great way to store carbon for centuries that would have been released into the atmosphere if the woody debris were just left to rot or burned in open piles. Our partners at the Blackfoot Challenge are working with local growers to do small field tests of the biochar on their land. Anything that can improve pasture and raise a rancher's bottom line is worth a try.

Now, we won't be running out and buying one of these babies anytime soon. To start with, there are only a handful in the U.S. and a waiting list to get ahold of one. Negotiating the beast through narrow, muddy logging roads also wasn't easy. But we are happy to be part of testing the feasibility of finding a way to use a byproduct of thinning that is good for the environment and holds the promise of some economic return on our restoration efforts.

A shout out to the U.S. Forest Service Missoula Ranger District's Wildfire Adapted Missoula Joint Chiefs Landscape Restoration Partnership and the Department of Natural Resource and Conservation's Montana Forest Action Plan for supporting this work.