Hybrid Forest Trees

by PALMER STOCKWELL and F. I. RIGHTER

SOON THERE will be hybrid forest trees that may grow to harvesting size in one-half or one-third the time required for a good, nonhybrid timber tree to reach the same size. Our forests and farm wood lots, where planting is practiced, might then be made to produce twice or three times the volume of timber that would be produced by planting standard stock or letting natural growth populate the site.

Already we have a hybrid pine, that at 3 years is more than twice as high and three times as heavy as the better of its two parents. So, a new era is beginning in reforestation and, although the hybridizing of forest trees seems to be at about the same stage that hybridization of corn had reached in the mid-1920's and failures and disappointments are to be expected along the way, we confidently predict that in another 20 years the forester will be using and discussing hybrid tree strains as casually as Midwest farmers now discuss their hybrid corn.

This exciting new development did not come overnight.

In the last decade, it has become increasingly apparent that the forests of the world are not producing timber as fast as the world needs it—particularly timber suitable for construction, packaging, paper making, and kindred uses. So, the tree breeder is at work in many countries, developing new strains to increase lumber production. Most countries are now interested in the improvement of forest trees, but intensive breeding work is carried on in relatively few of them.

Australia and New Zealand, which, like much of the Southern Hemisphere, lack softwood timber, have been leaders in introducing and acclimatizing foreign species. Not having the source materials needed for extensive hybridizing, Australian and New Zealand scientists have concentrated on selection and propagation.

The Russians have made contributions particularly with their research on hybrid oaks and poplars. The British are among the leaders in the development and analysis of ideas pertaining to the breeding of trees. The interest of Swedish breeders centered on the production of superior varieties of aspen for paper pulp production and conifers for construction lumber, the result being that several valuable new varieties are being used in forest planting. They have taken advantage of naturally occurring giant forms of aspen and have encouraged the introduction of hybrid poplars from America. Even during the war a few German research workers continued their quest for faster-growing trees. As in Sweden and Russia, the poplars have received most intensive attention in Germany, although the long-sustained German interest in the conifers continues. Denmark has made great strides in the work; indoor techniques for dwarfing trees, forcing early flowering, grafting imported scions on potted rootstocks, and other ingenious devices have reached a high stage of development.

The Union of South Africa established a tree-breeding program in 1943. Its first efforts are directed toward improving the native wattles and the introduced pines. South Americans are aware of the possibilities of tree breeding. Outstanding work has been done on quinine and rubber in the Amazon Valley of Brazil by commercial operators. Other Brazilian scientists are interested in various other species. In Argentina, Peru, Colombia, and other South American countries there is a growing interest, but they have established no specific tree-breeding program as yet. The Canadian tree-breeding program represents the combined action of the Biology Division of the National Research Council with the Dominion Forest Service and the Department of Agriculture of the Dominion. In 1940 the poplar work alone resulted in the production of 10,000 hybrids. The work was largely discontinued during the war but has gained impetus since then. The poplar for paper pulp and match stock production and conifers for paper pulp and construction lumber remain the centers of interest.

Between 1935 and 1945 most of the forest-tree breeding projects in the United States were reduced or discontinued, primarily because of the improved techniques for making paper of other woods than poplar, reduced budgets of Government-sponsored breeding work, and the war. The programs of the Oxford Paper Co. and the Tennessee Valley Authority were practically discontinued; those of the New York Botanical Garden, Harvard University, and the Northeastern Forest Experiment Station suffered almost as much. Only the Institute of Forest Genetics was able to continue its program—and its work was reduced by more than half during the war.

Several fundamental differences between the breeding of agricultural plants and forest trees should be kept in mind.

In the breeding of agricultural plants, genetic uniformity is a necessity. For example, the varicolored corn of the Southwestern Indians cannot compete on the open market with uniform standard varieties. Lack of uniformity in a farm crop would spell financial ruin for the modern farmer. He enhances the natural uniformity of his crops still further by careful grading for size, color, and other qualities—a profitable practice.

But forest trees are genetically quite diverse, although they may appear to be uniform to the casual observer. Natural species owe their existence and perpetuation to variability, which enables some to survive attack by insects or disease and others to invade new environments or withstand changed conditions. Furthermore, the timberman is accustomed to using trees from forests of natural origin and variability does not disturb him as it would the farmer.