U.S. Forest Service considers using explosives to bring down treesPosted: May 30, 2012
Paul Bunyan wouldn’t have known what to make of Gordon Ash’s little logging crew in the Pioneer Mountains last week. Instead of axes or saws, the U.S. Forest Service team went after trees with sticks of highexplosive.
“You’d calculate the proper amount of explosive, and then fix that on the tree with shrink wrap,” Ash said. “You’d put it right where a face-cut would be, and sever it off right at the point where you put the explosive – almost like a directional fall. The idea is to link as many of those trees as possible to be efficient. In three and a half days, we did 500 trees.”
To be clear, this job went for quality, not quantity. Ash’s targets were beetle-killed pine trees overhanging parts of the Pioneer Mountain Scenic Byway in the Wise River Ranger District. Assuming the project pencils out, more blasters could take out stands of dead timber along highways in the Helena National Forest.
Blasting trees makes sense in certain situations, Ash said. Insect-killed trees in particular can pose hazards that healthy forests don’t. They often rot from the inside, making them prone to shattering or falling in unpredictable directions. Put that rotten tree on a cliffy hillside over a road, and there’s no safe way for a lumberjack or mechanical cutter to cut it down.
Explosives also help when a cut tree has hung up on its way to the ground. Those trees can get so twisted or bent that their tension makes it almost suicidal to touch them with a chain saw. Better to blast from a distance than trigger a natural booby trap, Ash explained.
“We just don’t have a whole lot of really good sawyers,” said Charlie Showers, engineering program leader at the Missoula Technology and Development Center. “The days of going out and doing that activity are long gone in the Forest Service.”
Interest in blasting hazard trees got started in Colorado, where huge swaths of forest have succumbed to mountain pine beetle infestations. Those dead trees threaten campgrounds, roads and other public facilities.
While the idea makes sense in theory, it takes a lot of on-the-ground practice before foresters feel safe to have it in the toolbox. Ash’s crew measured what their shock waves did to surrounding areas, how closely spaced the blasting pods could be, and other factors beyond what it took to detonate a tree trunk.
A blaster can exercise a remarkable amount of control in how the tree comes down. Drilling a hole in the trunk and putting explosives inside does very little damage to the wood, leaving a fuzzy stump. Shrink-wrapping explosives to the outside snaps the tree as if it were toppled by a wind sheer. Proper placement can bring down 50 trees at once, laying them “like hair on a dog’s back” for easy decking or removal, Showers said.
British Columbian loggers use explosives extensively, according to MTDC’s Robert Beckley. In addition to clearing hazard trees, they like to place fertilizer-based explosives at the base of decrepit cedar trees to tip them over without shattering them.
The ammonium nitrate-based explosives detonate more slowly than the emulsion-style sticks used in the United States. So they push more than they break, tipping the tree from the roots instead of snapping it at the trunk.
Beckley said he often gets questions about what the blasting does to surrounding wildlife. So far, he’s seen little effect – about the same reaction as animals have to a thunderstorm.
Last week’s experiment in the Pioneer Mountains explored, literally, the best bang for the buck.
The Forest Service needs to determine what kind of placements bring a tree down in the safest way, with the least explosive and the most efficient use of time and personnel.
So the crews tried to break down their actions into a forest assembly line, where some members would identify the target trees, others would place the explosives, and still others would connect the detonators.
“My gut feeling is telling me when you’re looking at massive amounts of trees on steep ground that you can’t get at with a 30-pound chainsaw, where you’ve got rot and limbs hanging them up in the canopy, I think this is really going to be a very viable tool for the ranger,” Showers said. “Where we can’t go in with logging equipment, explosives are the safest way, generally.”