PINE BREEDING IN THE UNITED STATES

J. W. DUFFIELD, PALMER STOCKWELL.

Trees fit into the general rule that the plants and animals which nature gave us have not been considered quite good enough. For millions of years, it is true, nature has developed a breathtaking variety of forms, each wonderfully adapted to its surroundings. Changes in climate or the conformation of the earth's surface have caused the extinction of some forms and the development and migration of others. But during the long development of civilization man has learned to alter some of the myriad forms of life about him, making them better suited to his needs.

Centuries of breeding have developed livestock and plants that have special value, but only recently has man applied his knowledge of breeding to the development of better forest trees. Much of this work has been done with pines because of their wide distribution and their value for many wood products. Today pine-breeding research has progressed to the point that promising pine hybrids exist for each of the major timber-producing regions in the United States.

How has this point been reached? And what are the results now ready for trial?

As long as man used only an occasional tree he was not concerned with replacing it. But when he began to fell sizable sections of the forest, he observed that the succeeding cover was often different from the one he had removed. To insure another tree crop of the type harvested, he often found it necessary to sow seeds or plant Young trees. This practice foreshadowed the beginning of forest-tree improvement, perhaps 500 years ago. In his early planting operations, the forester soon learned that certain local races of trees surpassed the average.

American foresters, influenced in their early work by European forestry,were quick to import one of Europe's leading timber trees, the Scotch pine, a species that, despite its name, extends from the British Isles into Siberia and from the Arctic Circle as far as southern Austria and the Iberian Peninsula. Foresters in New York State found that Scotch pine from the shores of the Baltic Sea made a respectable tree in their plantations, while the same species grown from south German seed produced gigantic corkscrews and other bizarre and useless forms. Foresters in almost every European country have studied Scotch pine from various sources and have come to recognize an almost limitless number of local races, each fitted by natural selection into the mold of the local climatic and soil conditions.

In the past few years, several workers in the Forest Service, notably R. H. Weidman, T. T. Munger, and W. G. Morris, have completed studies of local races of ponderosa pine and Douglas-fir, two of our most widespread and important western conifers. An interesting study of altitudinal races of ponderosa pine in the Sierra Nevada of California was initiated by L. Austin, also of the Forest Service. Work of this kind has led foresters to the realization that careful comparative studies of climate and soils and of the growth of local races should enable them to proceed with more certainty in their work of reforestation.

In recent years most spectacular results have been achieved by this analytical approach in parts of Italy, South Africa, Australia, and New Zealand regions that have rather meager native conifer forests and only moderate rainfall, most of which falls in the winter. Such a climate resembles that of coastal California, where a few small patches of natural Monterey pine survive. The fossil record shows that this pine once occupied a much larger area, but because of increasing dryness along the coast it was squeezed into a smaller and smaller area. There it was making its last stand when the botanists found it. Given a fresh start in Australia, New Zealand, Italy, and South Africa, this almost extinct pine delighted foresters by its -rapid growth and good form. In places where it was a complete stranger, it found just the conditions of soil and climate it needed.

These examples show the effectiveness of natural selection in shaping the heredity of trees so as to fit them for growth in specific types of environment. It would be surprising, however, if men were content with a process so slow that it can only be seen in the unfolding of the fossil record. Foresters have turned to artificial selection or sought some other man-made device to speed up the remodeling of forest trees.

Biologists generally agree that certain features of species are especially important to survival of the race. The features have to do with the survival of the individual and perpetuation of the species. Furthermore, infancy is the period in the individual's life during which the balance between survival and death is most precarious. Thus the features most strongly molded by natural selection, the so-called adaptive features, have to do largely with the start of life of the individual. The forester, however, is largely concerned with the characteristics of mature or young-mature trees. His selection has been aimed at the development of trees especially suited to producing usable products such as clear lumber, smooth veneer, or strong paper in the greatest possible quantities per acre per year. His selection therefore must take quite a different direction from the one practiced by nature.

Before our knowledge of the science of genetics was developed, selection was practiced in the woods. Seed trees of good form were left and misshapen wolf trees were cut, or, if plantings were needed, seed was collected only from the best-formed trees. With the recognition of Gregor Mendel's work at the turn of the century, some foresters realized that well-formed seed trees might carry in a recessive or concealed condition certain hereditary factors that could cause some of their offspring to be of an inferior quality. Other early work by geneticists showed that many characteristics of plants and animals such as size, quality, and resistance to unfavorable environmental influences were determined by many hereditary factors. So, for a tree to have the maximum growth rate or a certain form, it had to have just the right combination of a large number of hereditary factors. That fact revealed the relative ineffectiveness of selection practiced in the woods as a method of improving the heredity of a forest and eventually led to deliberate efforts to develop superior types of forest trees by genetic methods.

It is always difficult to point with certainty to the originator of an idea, and we hope to be forgiven if we unwittingly slight the "father of tree breeding." Klotzsch, in Germany, attempted to cross Scotch pine with Austrian pine in 1845. His statement that he planted the hybrid seed the spring following pollination is at variance with the facts, because 2 years are required for the formation of seed of those species. Nils Sylven in 1909 undertook to investigate the heritability of certain well-recognized crown types in Norway spruce and Scotch pine growing in Sweden. This he did by making self-pollinations to determine whether the various crown types would breed true. From 1912 to 1924, Augustine Henry, in England, and several Americans, including Helge Ness, A. B. Stout, E. J. Schreiner, and others, began controlled pollination work, the foundation stone of tree breeding.

In 1925, James G. Eddy, after seeking the advice of Luther Burbank, established the Eddy Tree Breeding Station at Placerville, in northern California. The station was later deeded to the United States, to be managed by the Forest Service as the Institute of Forest Genetics. The Institute soon narrowed the scope of its work to the genetic improvement of the timber pines. John Barnes, W. C. Cumming, and W. G. Wahlenberg pioneered in the development of pollination techniques. F. I. Righter joined the station staff in 1931 and, with W. C. Cumming, perfected the techniques and used them to demonstrate the great possibilities for genetic improvement that could be realized through species hybridization in the pines. At about this time, Philip C. Wakeley, also of the Forest Service, made a number of crosses between the timber-pine species of the Southeastern States.

Much of the pioneer work in pine breeding thus is behind us.