Researchers at Mississippi State University are collecting samples of cottonwood trees in the Southeast to preserve the genetic diversity of this species.
Eastern cottonwood is an important contributor to forestry in the United States and other countries, with attributes that make it potentially even more important in the future. Timber industries have traditionally been attracted to it because it is fast-growing and can be grown from cuttings.
Recently, Eastern cottonwood has been identified as the most promising tree species in the eastern United States for biofuels production.
Sam Land, forest geneticist in MSU's Forest and Wildlife Research Center, has teamed up with the U.S. Department of Energy, U.S. Forest Service, and the pulp and paper industries to study these trees. The work was prompted by the DOE's Biofuels Feedstock Development Program.
"We're trying to study and preserve the natural genetic diversity of native trees and develop genetically improved trees," Land said. "This is a classic tree improvement program."
Cottonwoods are a hardwood, but softer than most. They are also very fast-growing, reaching 8 to 9 inches in diameter and 40 to 50 feet tall in five years. They are uniform trees and can make a profitable farm crop.
In the 1970s, the U.S. Forest Service at Stoneville began researching cottonwood genetics and released some new varieties. They closed this project in 1981, and Land salvaged what he could of their material and began collecting his own samples.
"My objective was to get a collection of Eastern cottonwoods from throughout their natural range in the southeastern United States. This includes North Carolina and Florida to central Texas and up to southern Missouri and Kentucky," Land said.
"This collection will preserve samples of genes in the native population from being lost to urban sprawl or bottomland flooding by dams and reservoirs," he said. "The collection also will provide the plant material needed for studies of the basic biology of this species and for tree improvement breeding."
Land divided the Southeast into six smaller subregions, with three east and two west of the Mississippi River and one in the Lower Mississippi River Valley. Samples already had been collected from the two sites west of the river, and from the river valley. Land's group located 72 natural stands in the three other subregions, with 24 stands identified from each subregion.
Seeds were collected and cuttings made from individual trees in each subregion. Orchards and nurseries were established in Mississippi, Louisiana and Florida to house samples of each of these trees. Cuttings provide clones of the trees from which they are taken, while breeding generates seeds that grow new trees not identical to either parent.
"Orchards and nurseries are central repositories of natural diversity," Land said.
Four field trials are being conducted to determine the fastest growing and most disease-resistant cottonwood varieties. These sites are located in south-central Florida, southeast Missouri, west-central Alabama and northeastern North Carolina.
"We're trying to find the best families and make crosses of these trees to improve them genetically," Land said. "With cottonwood's ability to propagate by cuttings, you can find the best individuals and multiply them many times."
By collecting and breeding trees, researchers are trying to preserve the genetic diversity that exists and find the best cottonwoods for a variety of uses. A primary goal is to develop a fast-growing source of cellulose that can be converted to fuels.
"We want to find rapidly grown trees to produce wood that can provide wood alcohol, or ethanol, for fuels," Land said. "Ethanol is an alternative, renewable source for fuels."
Land said there is a growing demand for ethanol, especially in light of the recent surge in crude oil prices reminiscent of the oil crisis of the 1970s.
"The primary argument is to get away from dependence on foreign oil," Land said. "It may cost 10 to 20 cents more at the gas pump to use ethanol, but the process for producing it is clean for the atmosphere and is not affected by international politics."
The traditional fuels of oil and coal are non-renewable. As they burn, they release carbon dioxide into the atmosphere. Trees are renewable and although they release carbon dioxide when burned, they use more of this gas from the atmosphere as they grow. Land said this process reduces the carbon dioxide responsible for global warning.
"Timber companies also are interested in developing fast- growing cottonwoods for pulp and paper," Land said. "Both the timber and energy production companies are interested in the improvement of similar traits such as disease resistance and rapid growth."
The economic impact of developing genetically-improved trees will depend on how widely the improved material is used. As the market for these wood crops increases, the economic impact will also increase.
Land said cottonwood is expected to become more important to agriculture in the coming decades since growing these trees in an intensive five-year rotation can provide fiber, store energy "on the stump" and improve the environment.