HOUGHTON - Sugar maple forests are one of the Upper Peninsula's most abundant - and potentially most sustainable - natural resources, providing jobs for loggers and high-quality timber that's exported around the world, as well as recreation spaces.
But while most northern hardwood forest stands are professionally managed, few foresters follow the strict standards that would lead to the greatest long-term benefit, according to a recently-released Michigan Technological University study.
According to the study, which included both privately held, corporate and state-owned forests, only 23 percent of forests conformed to the Arbogast method, which for decades has defined how many trees of various sizes should be cut to maintain the optimal productivity of a stand.
Dan Roblee/Daily Mining Gazette
Dr. Robert Froese examines some pole-sized sugar maples marked for cutting on a corporately-owned forest in Stanton Township. He said the forest was in a second-growth phase after having been clearcut several decades ago.
The study said about 40 percent of stands were overcut, which could lead to diminished future yield, while about 36 percent of stands were undercut, which limited both their economic utilization and potential for new growth. Public, private and corporate forests all missed Arbogast targets at similar rates.
Dr. Robert Froese, one of the authors of the study along with Nan C. Pond and Linda M. Nagel, said reasons for varying from Arbogast may be valid, but foresters and landowners should recognize the effects of those decisions.
"It's important to understand when we're not doing Arbogast but think we are, what the consequences are," he said.
The Arbogast method, he said, leaves numerous trees of various sizes, cutting enough to provide light and space for new growth while leaving enough trees to provide some shade and maintain forest quality.
"By maintaining the right number of trees at all times, the trees get tall and straight, which creates high quality boles so that 50 years from now we get high quality saw timber and veneer," Froese said.
The good news, according to Froese, is that almost none of the forest stands studied had been clearcut or catastrophically managed in other ways.
"All of the stands we sampled except one used some kind of selection sample," he said.
"On average, they clearly had the intent of leaving behind different size trees, with some thought to the future."
That means those stands should regenerate successfully, he said, just not necessarily as well as they would under strict Arbogast management.
Generally, Froese said, when private or corporate forestry practices varied from Arbogast, it was to meet landowner objectives of greater short-term financial gain, or to lengthen the period between one cutting and the next.
Forestry consultant Jerry Grossman's company, Grossman Forestry, manages about 350,000 acres of privately owned land, and while he calls the Arbogast method the "holy grail of forestry," he also agrees it's been "modified many times for different landowner objectives."
"It's like having a goal, you kind of approach it but never quite get there," he said.
Some factors that can lead to non-Arbogast decisions include weather issues, soil variations and pestilence.
"The whole peninsula is dealing with the ash borer, everybody's reacting to invasive species, and reacting to past management," Grossman said.
Mark Korkko, who manages corporate forest holdings for Molpus Timberlands, says his company takes Arbogast into consideration, but uses a variant of the method.
"We maximize for economic potential, as well as for the future," he said.
A primary difference, he said, is that Arbogast values lots of large trees left in the forest, whereas corporate clients would rather cut more of those trees.
"The economic value of those trees, once they get past a certain point, they decline," Korkko said. "At some point, as soon as the tree reaches a certain size class, you're trading quantity for quality."
Publicly-owned forest lands, according to Froese, tend to have a different problem - underharvesting, by the Arbogast standards. The dense canopy left behind can make it difficult for those forests to regenerate, he said.
Often, "They could have cut more and sold it and put money into the economy and still done well under Arbogast," he said.
In general, Froese said, while his study showed room for improvement in long-term management - and in transparency among foresters who say they're using Arbogast but fall short of the mark - it also revealed mostly responsible management overall.
"We're not doing Arbogast that often, but we're not doing that badly," he said. "Could we do better? Perhaps. It depends on what you want from your forest."