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Bill Berguson

Bill Berguson and a young poplar. Berguson leads the U's poplar tree breeding program at NRRI in Duluth. The program is one of the largest in the world to develop hybrid poplars for industry.

Fast-growing trees for fuel and fiber

U researchers developing hybrid poplars as a biomass energy option

By Pauline Oo and Jeff Falk

May 26, 2006

In times of high fuel prices, the demand for homegrown renewable energy is at an all time high. The University of Minnesota, Duluth's Natural Resources Research Institute (NRRI) is spearheading an array of projects aimed at meeting the growing demand for biomass energy. One of those projects involves hybrid poplars, some of the fastest-growing and most productive trees in North America.

"Gas prices have almost tripled in the last few years, and that's really caused a dramatic shift in what the economics of biomass could be," says Bill Berguson, director of NRRI's forestry program. "We're seeing [an increase in the] commercial applications of biomass energy." Gasifiers and ethanol plants that convert biomass waste products into energy are cropping up in mills and manufacturing facilities across Minnesota, he adds.

"There's a gasification plant at Little Falls that is biogas fueled," says Berguson. "There's also a large project, which is a joint venture between the municipalities of Hibbing and Virginia, that's going to burn biomass to fuel their facilities, provide heat for the homes in both cities, and [produce power for] the electricity grid. That [large-scale application] would not have happened a few years ago. The economics just wouldn't have been there."

Corn is currently the most developed biomass energy source in the United States, and researchers across the nation are evaluating other potential energy crops, including alfalfa, soybeans, hemp, and switchgrass. Berguson and his team have chosen to study hybrid poplar trees. The NRRI poplar tree breeding program is one of the largest in the world to develop hybrid poplars for industry.

Hybrid poplars can produce three to six times more wood per acre per year than natural forests, according to the Minnesota Department of Agriculture. Its productivity makes it well suited as a source of bioenergy (such as heat, power, and transportation fuels), fiber (paper, pulp, or particle board), and other biobased products like organic chemicals and adhesives. Compared to corn and other annual row crops, the hybrid poplar (and other perennial plants) is an ideal biomass alternative because it can greatly reduce erosion and runoff.

"It's an important part of the forest industry right now," says Berguson. "Hybrid poplar is planted on agricultural land [and] grown pretty much like a corn crop. Intensive management, weed control, and fertilization are part of why you get the fast growth. [The other part] is optimum genetics."

Hybrid poplars are members of the willow family, but they represent crosses among various cottonwood species.

"What we do is take the eastern cottonwood, which is native to Minnesota and a large part of the United States, and breed that with pollen from Japan, Korea, and parts of Europe, such as Italy," explains Berguson. "It takes a concerted breeding effort to produce a hybrid poplar."

A young poplar tree
A hybrid poplar can grow to a height of 60 feet in 10 years.

But it's worth it, he adds.

"You can grow a 60-foot-tall tree in 10 years," says Berguson. "And there is an industrial application of hybrid poplar in Minnesota on agricultural sites to produce wood primarily for paper production. International Paper [for example], is planting fairly large acreages of hybrid poplar to provide wood at its paper mill in Sartell, Minn."

According to the Minnesota Department of Agriculture, hybrid poplar trees can be harvested on 5- to 15-year cycles and often regrow from the roots and trunks, eliminating the need to replant.

NRRI's hybrid poplar research is focused on reducing costs by improving yields, increasing pest and disease resistance, and developing efficient management systems. To date, NRRI has bred poplar hybrids with more than 5,000 genotypes that are disease resistant and that will grow on marginally productive croplands, such as those in northern Minnesota.

"There is a lot of interest in using a variety of biomass sources, not just the hybrid poplar plantations themselves but residues from forest harvest operations and even biomass from brush lands," says Berguson. "All of those sources are being explored by us and others to see whether they are economical, what the volumes are, and how much energy you could actually derive from those sources."

Not only are biomass projects like the U's poplar breeding program important for energy independence, they are vital to Minnesota's economic development. Renewable energy is also one engine powering the University of Minnesota's drive to transform itself into one of the world's top three public research universities.

"There are projects that are starting that will result in additional revenue for loggers and keep the cost savings here in Minnesota, rather that exporting those dollars to Texas or the Middle East," says Berguson. "Those projects stay here and generate jobs locally, so that's really been a major change from the last few years. Biomass energy has really started to come into its own and become economically viable. And Minnesota is on the forefront of the development of biomass energy."

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