Ready, Set, Grow

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Hybrid poplar trees are attracting attention as an alternative crop for Oregon agriculture.

They don't grow from magic beans, but the brisk pace at which hybrid poplars sprout up towards the sky does suggest a comparison with Jack's beanstalk. For example, the average Douglas-fir grows two feet in the first year of growth under good conditions. A hybrid poplar is explosive by comparison, averaging 10 feet of growth in the first year under good conditions.

It doesn't actually reach up to the clouds overnight, but a hybrid poplar tree can be ready for harvest in 7­14 years, about a third of the time it takes for a Douglas-fir to reach harvestable size of 12 inches in diameter near the base of the tree.

This quick-grow capability has made hybrid poplar attractive to the forest products industry and to agricultural producers. The industry sees hybrid poplar as an alternative source of wood fiber for paper and other timber-based products. Producers see hybrid poplar as an alternative crop that they hope will be profitable, if markets for the trees develop.

Their fast growth rate isn't the only thing hybrid poplars have going for them. Willamette Valley farmer Rob Miller describes the trees as a "wonderful" example of agro-forestry-the production of a forestry crop on agricultural land with standard agricultural production techniques.

They can be grown on flat land in evenly spaced rows and cultivated, fertilized and irrigated just like other agricultural crops, Miller said. And, hybrid poplars are useful for erosion control, stream bank stabilization and wildlife habitat restoration, he added.

Man walking among poplar trees.

Rob Miller, owner of Mt. Jefferson Farms near Salem, looks at hybrid poplar trees he planted a year ago in a 30-acre plantation. The trees average 12-15 feet in height, with some even taller. They'll be ready to harvest in 12 years. Photo: Bob Rost

Because they grow fast, hybrid poplars quickly develop a root system that takes up a lot of moisture, and nutrients such as nitrogen and phosphorus, as it expands. Poplars serve to anchor the soil, particularly in stream bank areas, while removing excess nutrients from water runoff before it enters streams.

Some growers take advantage of these characteristics by planting hybrid poplars in rows along stream banks to help improve stream water quality. In western Oregon some growers have found hybrid poplars a good alternative crop on wet soils that are poor for producing grass seed and other field crops. The poplar's thirsty nature helps it grow very well on agricultural lands that remain saturated with water for long periods of the year.

Their natural tendency to readily take up nutrients from soil and irrigation water has made hybrid poplars useful as a water treatment tool. Some cities around the state are using hybrid poplar plantations as a component of their water treatment facilities. And, the trees provide habitat for wildlife, particularly birds.

All these pluses make hybrid poplar sound like a pretty good bet for Oregon agriculture, but one big question remains-will there be good markets for the trees?

Initially, hybrid poplars were developed as a potential source of pulp for paper production. However, currently it's cheaper for paper companies to import pulp than to buy it from domestic sources. As a result, there has been a switch to growing hybrid poplars for use in solid wood products such as peeler logs for plywood, door frames, finish moldings and window sash material. But the market for poplar wood is still developing and its potential is unknown.

Whether it's pulp or solid wood products, David Riddell of Riddell Farms Inc. believes a good market for hybrid poplar will be found.

Man bending over a small poplar tree.

Clint Shock, superintendent of the Malheur Experiment Station, established a trial plot of hybrid poplar trees on station grounds near Ontario in 1997 to evaluate the trees for eastern Oregon growers. The evaluation study was part of a regional economic development program. Photo: Bob Rost

One of the first growers in the Willamette Valley to try the trees, Riddell farms 4,300 acres, mostly grass seed, near Monmouth and has 200 acres of hybrid poplars. He started planting the trees in 1990 and is planning his first harvest of hybrid poplars this fall.

Growing the trees as an alternative crop "is like investing in the stock market," Riddell said. "It's a long-term investment."

Don Wirth, a grass seed grower near Shedd, agrees. Wirth has 150 acres of poplars on his 3,000-acre grass seed farm.

"You've got to be optimistic about it," he said. "I don't know what the markets will do, but I planted the trees because I thought they would become a crop."

The hybrid poplar varieties Riddell and Wirth are growing had their origins in a Pacific Northwest forestry research project that began in Washington state three decades ago.

In the 1970s the U.S. Department of Energy and the University of Washington started a project to develop poplar trees as an alternative source of wood fiber for paper production, said Steve Strauss, OSU College of Forestry researcher. Researchers at the University of Washington conducted research on cross-breeding poplar species native to the Pacific Northwest with many other species of poplar that grow throughout the Northern Hemisphere.

"They found that some of the hybrid tree lines they developed had remarkable rates of growth, as much as double the average growth of native poplar trees," Strauss said. "In addition, researchers noted that these hybrids were not sensitive to changes in climate-they grew equally well just about any place in the Pacific Northwest."

These findings were appealing to the paper industry, and in the 1980s Fort James Corporation, a manufacturer of paper products, got involved in the development of hybrid poplars as a source of pulp for paper production. Riddell and Wirth have both worked with Fort James Corp. researchers in establishing plantations of hybrid poplar.

Hybrid poplar's appeal as an alternative source of wood fiber for pulp grew in the 1980s and 1990s as the U.S. Forest Service began reducing the amount of public forest acreage available for timber harvest. However, by the late 1990s falling pulp prices dimmed prospects for hybrid poplar as a pulp product. Even so, the forest products industry and agricultural producers throughout Oregon remain interested in hybrid poplar as an alternative source of fiber for wood products.

Man standing in a grove of poplar trees.

The same Malheur Experiment Station hybrid poplar trial plot three years later. Photo: Bob Rost

In support of this continued interest in these wonder trees, the OSU Agricultural Experiment Station is conducting research to find ways to make hybrid poplars even more productive.

OSU Agricultural Experiment Station horticulture researcher Tony Chen has been using gene technology to find ways to make hybrid poplars grow later into the year.

"This is important for two reasons," Chen explained. "First, extending the growing season will increase yields, and second, producers grow poplar for fiber and the quality of the fiber produced by the tree is better later in the season than in spring or early summer."

Like all plants, hybrid poplar trees begin growing in the spring when temperatures rise and stop growing in the fall when shorter day length and falling temperatures signal the onset of winter.

The typical Oregon growing season for poplar extends from the first of April to the end of August in high elevation areas, and to the first of October in lower elevation areas of the state.

Man looking at glass containers of hybrid poplar plants.

Oregon State University forestry scientist Steve Strauss is using gene technology to develop hybrid poplar varieties that have resistance to herbicides and pest insects. Photo: Lynn Ketchum

"To extend the tree's growing season, while ensuring the tree will survive the winter, it is necessary to find out how the tree genetically controls when it starts growing in the spring and stops growing in the fall," Chen said.

Once this growth-cycle gene is identified, Chen says it can be used as a genetic marker in poplar breeding programs to select trees that have the longer-growing-season traits researchers are looking for.

A genetic marker is a reference point on a chromosome. Chen is searching for the poplar's growth-cycle gene by developing a map of the poplar tree's chromosomes. This map-called a genome map-is a chart showing where genes are located on the chromosome.

"When we can identify the gene that is responsible for the desired growth characteristic, we will be able to isolate the gene and transfer it to a genotype, or hybrid poplar variety, that can be grown as a new tree that will continue growing later in the year," Chen said.

Steve Strauss is also using gene technology in research on hybrid poplars. He is conducting a project in the OSU College of Forestry to try to identify and isolate genes for disease resistance in the trees.

"The purpose of the project is to create a catalog of these genes so we can use them to introduce disease resistance into hybrid poplar varieties that are susceptible to various types of disease," Strauss said.

In addition to being sensitive to disease, hybrid poplars are also very susceptible to weed competition.

"These trees need a lot of water, a lot of nitrogen and a lot of sun while they are getting established right after planting," Strauss said. "They don't compete well with other plants so growers usually use herbicides to keep poplar plantations weed-free."

Man pruning poplar branches.

Rob Miller, owner of Mt. Jefferson Farms, prunes a year-old poplar in a plantation near Salem. The trees receive three prunings to promote the growth of 17-20 feet of clear wood in the bottom part of the tree. Miller has grown hybrid poplar crops for many years. Photo: Bob Rost

However, the trees are just as susceptible to some herbicides as the weeds are, so Strauss is experimenting with genes that express herbicide resistance. His goal is to use these genes to develop herbicide-resistant hybrid poplars that aren't affected by chemicals sprayed on weeds around the trees.

Researchers are also developing hybrid poplars that are resistant to insect pests such as the cottonwood leaf beetle.

In eastern Oregon at OSU's Malheur Experiment Station near Ontario, researchers are studying weed control and irrigation strategies in poplar plantations as part of a region-wide effort to evaluate hybrid poplar as an alternative crop for agriculture.

Growers on the east side of the Cascades became interested in hybrid poplars in the early 1990s, and by 1995 they had established trial plantings at several locations in Malheur and Baker counties.

The results were "impressive," according to Marilyn Moore, OSU Extension agent in Malheur County. Based on that early success, she and a group of interested growers applied for and received a $225,000 three-year grant from the Oregon Economic Development Department in 1996 to develop hybrid poplar as a crop in eastern Oregon. Moore served as coordinator of the grant.

"Hybrid poplars grow very well here because they are cross-bred with native black cottonwood that is common throughout eastern Oregon," said Moore. "Many growers here think it's possible to grow a harvestable tree in 8 to 10 years."

Growers in eastern Oregon believe they will find a strong market for poplar as raw material for solid wood products, but they won't know for a few years. The first harvest of hybrid poplar in eastern Oregon is still four to six years away. Even so, Moore thinks the timing is right.

Man standing by table.

Ray Ethel displays a table made of chipped poplar wood in his office at Broadacres Nursery near Hubbard. Ethel's two-story office structure is built almost totally of poplar to show the many ways this wood can be used in the construction of homes and other small buildings. Photo: Bob Rost

"The declining timber harvest on public forest land will likely increase the shortage of wood fiber, which should create more demand for alternative sources like hybrid poplar," she said. "And growers here believe they can produce a high quality tree by paying special attention to tree spacing at planting, weed control, irrigation, and by pruning to promote high quality wood growth in the lower part of the tree," she said.

Clint Shock, agronomist and superintendent of the Malheur Experiment station, and his colleagues are studying ways to help growers grow quality trees. He is conducting a pruning study, and has already completed research projects on various approaches to irrigation management and weed control. Shock has also looked into the possibility of using cover crops in poplar plantations.

A cover crop might be any low-maintenance crop such as alfalfa or wheat that growers plant in rows between trees to help hold down weed growth in the plantation, Shock said.

In addition to cover crops, Shock and colleague Peter Sexton from OSU's Central Oregon Agricultural Research Center, Madras, are looking into the feasibility of intercropping in poplar plantations. Intercropping is the practice of planting a high value crop in the rows between trees. This gives growers the benefit of annually producing an income-earning crop during the first years in the poplar plantation while they continue growing the trees for the 8­12 years until harvest.

Shock believes intercropping could be especially important in eastern Oregon where the relatively dry climate requires growers to irrigate poplar plantations.

Man standing among poplar trees.

Tim Deboodt, OSU Extension agent in Crook County, is monitoring a trial plot of hybrid poplars at the OSU Central Oregon Agricultural Research Center, Madras. Agricultural producers in eastern Oregon are interested in growing hybrid poplars for the solid wood products market. Photo: Tom Gentle

"Irrigation costs can be very high, particularly if growers have to pay for electricity to pump the water they need," Shock said. "Annual earnings from a high value intercrop could help offset tree establishment costs."

So far, studies suggest that cover crops and intercropping don't work very well in hybrid poplar plantations between narrow tree spacings, Shock noted.

The trees are so sensitive to competition from other plants for water and nutrients that, at this point, it appears the best way to start a poplar plantation is to eliminate all competing plant growth as much as possible, Shock said, especially during the plantation's first year.

Cover crops are not very productive in the years following establishment of the plantation because by the third and fourth years, the poplar trees grow so high that their branches shade the area between the tree rows, reducing the amount of sunlight available to cover crops.

Shock and Sexton plan to study intercropping in hybrid poplar plantations using wider row spacings and denser tree spacings within the tree row as part of a proposed 3-year research program that will start in 2001. The changed tree geometry might allow successful intercropping, said Shock.

The program will include research projects on irrigation management, soil quality improvement, wildlife habitat and analysis of production costs.

Man reaching up a poplar tree.

Frank Sinclair has found hybrid poplars to be an effective tool for waste water management. Sinclair, superintendent of the Woodburn Waste Water Treatment Plant, has supervised the establishment of 85 acres of hybrid poplars near the Woodburn facility, which was the first to use poplars in waste management operations. The trees are ideally suited for this use. Photo: Bob Rost

As growers and researchers learn more about these trees, they hope to answer many of the questions about how this crop will fit in on the farm. The general consensus is that eventually hybrid poplars will be a good crop for Oregon agriculture-kind of like the beanstalk, which turned out to be a pretty good thing for Jack.

Concerning the development of markets for poplar wood fiber, many agree with Scott Leavengood, an OSU Extension Service agent in Klamath Falls who works in forest products manufacturing.

"It's a guessing game right now, but I think the markets will be there," he said. "The wood products industry here is interested in hybrid poplar, but it will take some time for them to decide how they want to use it."


The quick-growing hybrid poplar varieties popping up in plantations around Oregon today have quite a history. They are part of a research effort that spans the 20th century and includes contributions from university horticulturists and forestry industry researchers throughout the country.

The group of trees collectively known as poplars includes aspens, cottonwoods and balsam poplars. The cottonwoods and balsam poplars have been used in most of the cross-breeding research in the United States over the past 50 years. Joseph Illick, author of a book called "Tree Habits" published in 1924, wrote, "Among the principal merits of the Cottonwood are the ease with which it may be propagated, its rapid growth and its tenacity of life." Illick went on to note that the cottonwood grows easily from cuttings (a major reason why this and other poplars are easy to cultivate), and that it is nearly impossible to kill.

The cottonwood's hardiness and fast growth have made it a popular tree for use in windbreaks and as a shade tree since the pioneer days of the 19th century.

According to Brian Stanton, research associate for Fort James Corporation, the first poplar hybridization project took place about 1900 at the Kew Botanical Gardens, West Sussex, England, and was conducted by Augustine Henry. In 1923, the Oxford Paper Company sponsored a poplar cross-breeding program conducted by researchers at the New York Botanical Garden in the Bronx. The goal of the project was to produce improved poplar varieties for paper production, and thousands of new varieties were developed, including one designated OP367 (Oxford Paper 367) which is used in eastern Oregon today.

Since mid-century, various other cross-breeding projects involving aspen, eastern cottonwood and black cottonwood have been conducted by the U.S. Forest Service, the U.S. Department of Energy, several of the country's universities and private industry.

Hybrid poplar research took on a Pacific Northwest focus in the 1970s with the project started by the U.S. Department of Energy, the University of Washington and Washington State University.

Published in: Innovations, Economics