Purdue Knocks on Wood to Produce Sturdier Trees

Molecular biologist Keith Woeste squats down among rows of young, musky-smelling black walnut trees and grasps one tree’s trunk to eye a slender branch.

These aren’t ordinary black walnut trees -- they’re integral to an ambitious bid by Purdue University scientists to create faster-growing, richer-grained and disease-resistant hardwood trees.

The goal is superior black walnut, black cherry and northern red oak trees -- a trio coveted by the fine furniture and wood flooring industry -- that can be planted by the millions in tree plantations.

“If we can domesticate hardwood trees, that means you can eventually leave the wild ones where they are in the woods because you’ve made something that’s better,” Woeste said.

For generations, people have been breeding better crops, fruit and decorative trees and prettier flowers. But until recently, there has been little work on improving hardwood trees.

Woeste believes that they can grow better hardwoods through a combination of classical breeding and biotechnology to give a boost to the nation’s $14-billion-a-year hardwood industry.

Researchers are crossbreeding the most desirable black walnut trees at Purdue’s experimental tree farm using grafted limbs selected from 400 different trees. They hope to produce black walnut trees with a higher percentage of heartwood -- the durable, coffee-dark wood made into expensive furniture.

Similar work is under way on black cherry and northern red oak at the center, a partnership created in 1998 between Purdue, the U.S. Forest Service and the Indiana Department of Natural Resources.

But the big leap forward may come when researchers begin genetically modifying select trees by inserting genes into embryonic trees with such sought-after traits as insect resistance.

Within five years, the center’s scientists hope to have created a new black walnut tree equipped with a gene that makes it resistant to herbicides. Such trees would boost large-scale hardwood tree farming by allowing tree farmers to kill weeds that threaten to choke out young plantation trees without damaging the trees themselves.

Researchers then will work to insert insect-resistant genes into black cherry trees to ward off attacks by insect borers that ruin the trees’ value.

If such improved trees eventually emerge, the center will be able to use simple biotechnology to produce millions of cloned seedlings for planting in the nation’s central hardwood region.

This 12-state area, stretching from Iowa to Pennsylvania to Tennessee, originally was covered by dense forests filled with towering oaks, walnuts and other ancient hardwoods. Nearly all of these old-growth forests were felled in the 19th century, in part to help build the East Coast’s great cities.

Although demand for North America’s hardwood trees grows each year, there is an annual shortfall of about 55 million seedlings.

Breeding efforts for loblolly and slash pines in the South have had the kind of success that Purdue is hoping for. By crossbreeding the most productive trees and developing “seed zones” that dictate where each improved variety should be planted, the inventory of wood from those trees has been boosted by 70%.

The Purdue center, which has a staff of 33 and a yearly budget of about $1.5 million, is surveying hardwood forests in the Midwest as part of its goal of creating similar hardwood seed zones.

But its research goes beyond industrial production issues to assessing the biodiversity of the remaining hardwood forests.

Nearly 90% of the nation’s annual hardwood production comes from private forests averaging less than 100 acres -- small patches that Woeste describes as “lifeboats of diversity.”

The best and biggest trees are typically taken during periodic harvests, and that could fuel the gradual decline in the size of hardwoods reaching the marketplace, said Paul Houghland Jr., executive manager of the National Hardwood Lumber Assn.

“The overall picture has been that the trees that are being harvested now are smaller than they were 50 years ago. And smaller trees mean you need more of them to get the same amount of lumber,” said Houghland, whose Memphis, Tenn.-based trade association represents hardwood producers and users.

More disconcerting than the size of the harvested trees is concern that stunted, diseased or otherwise undesirable trees left behind could weaken the genetic pool of hardwood species.

The Purdue center is cataloging and preserving tissue from a full spectrum of each species because many rare selections are in danger of becoming extinct.

Jeanne Romero-Severson, an assistant professor of quantitative genetics, is leading the center’s northern red oak project. Her task has particular urgency because oaks used for superior wood flooring are not long-lived -- 250 years at most.

“We’re now reaching the end of the natural life cycle of the trees that were here before the wave of European colonization, and we’d like to be able to capture that genetic diversity before it’s gone,” she said.

Unlike black walnut and black cherry, northern red oak cannot be grown from cuttings, but Romero-Severson is hopeful that the center can overcome that roadblock.

Her work surveying Indiana’s older growth forests has already led to the discovery that two old-growth woods in southern Indiana contain unique northern red oak populations. The stands are descendants of trees destroyed when mile-high glaciers flattened the northern half of Indiana about 14,000 years ago during the last Ice Age, she said.

The center’s staff is always on the hunt for seeds or branches of rare trees, such as those with curly or wavy grains that can fetch 10 to 50 times the price of normal grained hardwoods.

The hardwood-improving genetic technologies the center develops could also help ward off future disease threats such as a fungus threatening California’s majestic oaks and redwoods.

“It’s diseases like that we need to be prepared for because we know that hardwood trees -- the American chestnut, the American elm, for example -- can be decimated in a matter of decades by disease,” Woeste said.