The quest for the super trees is taking foresters from the woods to the lab
It's a Bunyanesque dream long held by foresters: stands of towering, straight , quick-growing trees that yield more planks and pulp per acre than your standard pine in the woods.
Today's commercial timberlands aren't yet dominated by such super trees. But through an expanding use of conventional tree-breeding techniques, coupled with efforts to harness the powers of biotechnology, foresters are moving closer. Their goal: trees that grow taller and produce more wood, are more resistant to diseases, and survive in harsher soils than their cousins of today.
The pressure to breed superior species stems from a growing need to produce more lumber and paper from limited timberland. Foresters have been aware of this need since at least the 1950s. But only recently has science begun to make an impact in the woods.
The first attempts at tree improvement were simple enough: Foresters planted seeds collected from what they considered the best trees in the forest.
Nowadays the process is more complex. Foresters still tromp through the woods to find trees that exhibit superior qualities. They then use high-powered rifles to shoot twigs off high branches (''a time-consuming job if you're not a good shot,'' says one forester). The cuttings are grafted to rootstocks and planted at a nursery. After a few years the seedlings produce flowers, which are sprayed with pollen from other selected trees to create high-quality hybrids. The process can then be repeated, using the best conifers in the grove, to breed better trees with each successive generation.
Simple enough, yes, but there are snags. For one thing, the process is time consuming. While farmers can turn out two or three generations of wheat in a year, it takes eight to 12 years for a hybrid tree to yield seeds. It takes several decades more before it can be turned into furniture or paper.
It's also tough to choose a pine in the woods to use as a parent. It's not always clear, for example, whether a high-quality tree is the result of genetic makeup or good soil. Then, too, there are the usual failures involved in any plant breeding. David Borem, a forest manager for Georgia-Pacific Corporation, estimates that 1 in 5 branch grafts don't take.
To the large timber companies, though, breeding super trees may bring redwood-size returns. Foresters assert that first-generation stands now maturing , mainly softwood trees such as loblolly pine in the South and Douglas fir in the West, should increase pulp and lumber yields by 10 to 15 percent per acre. Bigger gains may come in succeeding generations. ''How far can we go?'' asks Robert Weir, director of the industry cooperative tree-improvement program at North Carolina State University. ''In corn they are still making gains after 80 generations.''
Super-tree breeding, not surprisingly, is on the rise. More than 80 percent of all replanting in the South, the nation's ''woodbasket,'' is now first-generation stock. Companies are working on second- and third-generation trees in their nurseries. Once confined to the South and West, the practice is now carried out by timber firms and state forest services across the country.
Interest is building, moreover, in work with trees other than conifers. In the upper Midwest, for example, foresters have had some success in reducing the time it takes for walnut trees to produce nuts. In Vermont, breeders are trying to create maples that will drip sweeter sap. Quick-growing shade trees are another goal of research.
The big new frontier in super-tree development, however, will be to create exact replicas (clones) of fast-growing, disease-resistant species. The idea is to take a bit of tissue from a tree and, by treating it with chemical brews, cause it to sprout shoots and roots in a petri dish. Eventually the clone could be planted in soil.
The big plus: Scientists could create several hundred trees or more from one select pine. The progeny, in theory, would also be genetic copies of the parent - thereby avoiding hazards inherent in crossbreeding (passing on of unwanted traits, for instance). And trees could be turned out more quickly. With conventional breeding, it takes eight to 12 years to produce a seed-bearing tree. With cloning, a tree could be moved from beaker to soil in one to two years.
Except for a few species, however, the technique remains experimental. A handful of universities and timber companies are working on applying it to the big money spinners: loblolly pine and Douglas fir. North Carolina State researchers, for example, have created young trees from tissue cultures of pine seeds. But seeds are the product of crossbreeding and may carry undesirable traits. They are now working with cells from pine needles and buds - the next step toward the ultimate goal of cloning tissue from mature trees.
One danger in cloning and, to a lesser extent, in traditional super-tree breeding is that some unknown disease or insect could wipe out entire plantations of similar trees. But foresters believe they can maintain genetic diversity in the woods partly by breeding different trees for different sites.
''No forester would allow vast acreages of just one clone of a source,'' contends Cleatus Turner, a research and technology manager for St. Regis Corporation.