Minnesota Science
Vol. 45, No. 4
Aspen/Larch Project Seeks Better Tree For Paper Industry
by Larry Etkin
Are we in danger of outstripping the renewability of our forests? Many say we're cutting timber down faster than it grows back. But jobs and our environment require avoiding that problem. Potential solutions include developing "super trees" that grow bigger faster, or to improve the way we grow our trees on plantations. The Minnesota Agricultural Experiment Station has a major role in achieving those goals.
Wood product uses in the Minnesota region are mainly for the production of paper and flakeboard. Aspen is a major raw material, and it's being harvested heavily. It's about 40 percent of the region's, and virtually all of Minnesota's hardwood harvest. Forest resource managers accept the likelihood of a "maturity gap" occurring between harvestable crops in a few decades.
Super trees might fill that gap.
A single European tree has been the aspen breeding workhorse, though that may soon change through efforts of an aspen/larch project at the Grand Rapids branch experiment station. That parent tree, discovered in a Swedish forest 60 years ago, is unique. It has four sets of chromosomes, and these to increased fiber length and superior growth. It has been widely crossed with normal females of related species to create vigorous triploids for further selection and breeding trials.
But, "the genetic base is a little narrow with the triploid," says aspen-larch project manager Gary Wyckoff. "Not that we've got any numbers out there now that should cause any concern. But we felt to anticipate that concern, we needed to expand the number of parents involved."
Two new tetraploids artificially induced in native North American trees are now reaching maturity. That development is exciting for Wyckoff. "It gives us the opportunity to put our native tremuloides back onto tremula females. "
Silvicultural "soil/site" factors are also being looked at. "A given area of land and the soil beneath it and the moisture that reaches it create limitations. Now that plot of land, with that moisture and that nutrient situation, can only grow so much wood. Whether you put that wood on a few trees or on a lot of trees, you are only able to produce so much wood per acre.
"You can improve on that by putting in more efficient trees, trees that are more efficient in using a lower quantity of moisture and nutrients. And you can find the optimum number of stems per acre," explains Wyckoff. "We've found, for the most part, that somewhere about 500 to 600 stems to the acre, at least from a plantation standpoint, is where we want to be."
The project has also looked at short rotation, intensive culture: harvesting relatively young trees. With under 600 stems per acre, "we're saying that to get larger diameter trees, we accept wasting that sunlight at early ages, knowing we're not going to have to come in and thin that stand at a later stage," says Wyckoff.
"Trees like hybrid poplar are being grown on shorter rotation," he says. "Forest managers want to have the maximum amount of leaf area on that site early on, so they're converting as much of that site potential to wood in a very short period of time. They are content to harvest smaller diameter trees, with a higher proportion of branches and bark."
Short rotation is important to paper companies such as the James River Corporation, where geneticist Brian Stanton says, "we consider the work that the project is doing very pertinent and important to our efforts to develop new species as short rotation crops."
The university attracted the aspen/larch project to Grand Rapids when the Institute for Paper Chemistry moved from Wisconsin to Georgia. Its breeding research, begun in 1954, is one of the older hardwood programs in existence.
"One of the biggest strengths is its history of good cooperative efforts between the industry, universities, research facilities, various government agencies," says David Karnosky, director of the Center for Intensive Forestry at Michigan Tech.
"Breeding is on-going," Wyckoff points out. "You never really reach an end. You're upgrading, you're bringing in new genotypes, you're always trying to keep that variability present."
"I would agree with that, absolutely!" says Karnosky.
PHOTO CUTLINE: Egon Humenberger shows off one of the aspen/larch project's
triploid hybrids. The tree is only midway through its second growing season.