DIRECT SEEDING OF TREES

W. E. MCQUILKIN.

Growing tree seedlings in a nursery and transplanting them later to the field is the standard artificial means for establishing forest plantations. On good sites and poor, in wet years and dry, the use of nursery stock, properly grown and properly planted, has proved more likely to succeed than any other artificial method.

Direct seeding, which means sowing seeds in the field where the trees are to grow, thus bypassing the nursery and transplanting operations, under some conditions may be a simpler, faster, and less expensive reforestation method. Because of certain inherent drawbacks, however, direct seeding is not regarded as a method to replace planting on a wide scale, but rather as a useful adjunct to it by which, in selected situations, reforestation can be speeded up and costs reduced.

By conservative estimates, we now have in this country at least 30 million acres of land in need of artificial restocking. Obviously, any procedure that will facilitate getting this land back into forest production should be fully utilized.

ADVANTAGES AND DISADVANTAGES will first be considered. With proper procedures on selected sites, direct seeding may be done successfully at lower cost than for planting nursery stock. Furthermore, since direct seeding is not dependent upon maintenance of a nursery and the starting of stock 1 to 4 years in advance, it permits a degree of flexibility in reforestation programs according to availability of labor, allotments of funds, and the press of other jobs that is impossible with planting. If curtailment is necessary, seeds can be held over a year or so more easily than growing nursery stock; with expansion, seed usually can be procured upon shorter notice and with less advance planning. Also, seeding can be done over a considerably longer season.

Growth direct from seed in the field permits normal development of root systems. Transplanting at best entails mutilation of roots and a set-back in growth. Although most species seem to suffer no lasting damage when properly handled, many cases of poor growth and disease in forest plantations are believed to be caused by malformed root systems that result from improper or careless planting. Some strongly taprooted species seem by nature poorly adapted to withstand transplanting they typically suffer high mortality, and many of the survivors fail to regain the vigor of natural, undisturbed. trees. With direct seeding, all depressive after-effects of transplanting are avoided.

On very stony areas, direct seeding is especially advantageous. Successful planting at reasonable cost on such sites may be almost impossible because of difficulty in digging holes to required depth and in finding enough rock-free soil to make a proper refill around the roots. Trees starting from seed in such ground are able to extend their roots around and between the stones, and may make excellent growth.

Opposed to these advantages is one major disadvantage that relegates direct seeding to a secondary place; namely, that with a few possible exceptions ( such as on extremely stony ground) direct seeding almost always entails greater risks of failure than planting nursery stock.

Greater risks are inherent in the method. Because of greater palatability to wildlife, greater susceptibility to certain types of insect injury and diseases, smaller size, undeveloped root systems, and generally greater fragility, seeds and newly germinated seedlings in the field almost unavoidably are more vulnerable to injury and death or destruction by all the natural obstacles to plant establishment than are transplanted nursery stock. In the nursery, seeds and seedlings are given intensive care and protection during the highly vulnerable early growth period; such care cannot practicably be given in the field.

The natural obstacles most likely to interfere more in direct seeding than in planting are the rodents and birds, drought, competition or smothering by the surrounding vegetation, injuriously high surface-soil temperatures, frost heaving, insect pests, as well as the seedling diseases.

Of these, rodent and bird depredations upon the seed, and direct-heat injury from high soil temperatures are problems practically unique to direct seeding. Planters of nursery stock ordinarily escape them entirely, and nurserymen can feasibly institute control measures if required. In certain sections, throughout the Western States particularly, seeding without some form of rodent control generally is futile; in other sections, notably the southern Gulf Coast States, birds are the major problem.

Direct-heat injury and mortality (independent of drought effects) may occur among tender, newly germinated seedlings if the surface-soil temperature rises above 120 F. Such temperatures are not unusual on bare ground in full sun; considerably higher temperatures sometimes develop on black soil surfaces or south-facing slopes. In extreme cases, even transplanted nursery stock may be damaged.

Both seedings and plantings are affected by the other obstacles named, but in general seedings are more sensitive and more likely to fail as any factor or condition becomes increasingly unfavorable. Little trees starting from seed in the field are more subject to the damaging effects of drought, root competition from other plants, and frost heaving because of their less well-developed root systems; they are more subject to smothering by other plants because of their handicap in height. Certain insect pests, like cutworms and white grubs, sometimes are highly destructive to the tender young plants but ordinarily do not seriously damage the 1- or 2-year-old seedlings. Likewise, serious damage from certain of the diseases, notably damping-off, is largely restricted to the period during and immediately after germination.

Other lesser disadvantages of direct seeding as compared to planting are that it requires a good deal more seed per reforested acre seed that may sometimes be difficult to obtain and that it is a somewhat more painstaking type of work, especially with small-seeded species like most conifers, which germinate poorly unless the depth of coverage is carefully controlled.

With recognition that direct field seedings are inherently more sensitive to adverse factors than plantings, the art of successful seeding can be characterized as, first, the discernment and the utilization of the combinations of species, site conditions, and the seasons where natural obstacles to plant establishment are relatively few or present in mild degree; and, second, application of such treatments as are necessary and economically feasible for lessening the obstacles or modifying the factors most likely to cause failure.

SEVERAL PRINCIPLES AND METHODS:

Direct seeding generally should be restricted to the more favorable sites. These sites usually are characterized by fairly deep, mellow, loamy, and well-drained soils situated on lower slopes and benches with northern or eastern exposures, in coves, or on bottom lands.

Site selection is more important in dry climates than in the moister ones. In the Lake States, for instance, which average rather dry among the forest climates, direct seeding generally is an uncertain undertaking except on the lower lying parts of the areas known as sand plains. Extensive acreages of this formation are found in Wisconsin. Seeding tests in the sand plains have indicated good chances for success where the ground-water table lies between 2 and 5 feet from the soil surface, but increasingly greater risks of failure as the water table gets deeper.

Besides good soil and moisture conditions, sites favorable for seeding are characterized by relatively thin and open plant cover. This points to recent burns on forest land and to recently abandoned farm lands as being among the most likely situations for satisfying direct-seeding requirements.

Seeding can be done any time that field conditions permit from late fall to early spring roughly October through April in the North, with a somewhat shorter spring season in the South. Fall sowing generally is best because it allows the seed to after-ripen naturally on the ground and germinate as soon as the weather is favorable in the spring. With spring sowing, seeds that require afterripening must have been previously stratified at near freezing temperatures for one to three months. When no positive rodent-control measures are planned, spring sowing sometimes is advisable because of the shorter period during which the seeds are exposed to the foraging of the animals.

All experience indicates that direct seeding with most species in the western forest regions is futile without some form of rodent control. Effective control measures are of two types : Hardware cloth covers placed over the seeded spots, and poisoning the area before seeding.

Covers or "screens" of hardware cloth (3 or 4 meshes to the inch) are effective but relatively costly and inconvenient. They are made usually in a conical or dome shape to permit nesting for carrying and storage. At prewar prices, covers 6 inches in diameter could be made for about 4 cents each, and with reasonable care were expected to serve about 10 seasons. Thus, where seeding might be done year after year, the prorated cost per spot for screens could be reduced to less than one-half cent. Even at that rate, the cost runs around $5 an acre of 1.000 to 1,200 spots; to this must be added the labor cost of placing them on the spots, lifting them later. and storage. Obviously, seeding with screens offers little chance for reducing reforestation costs below those that are needed for planting. Their use clearly is out of the question for a private landowner with a small, one-season job.

The prepoisoning for rodents, before seeding, seems to offer the best promise of effective control at reasonable cost. Experimental trials of this method, as developed at the Northern Rocky Mountain Forest and Range Experiment Station in cooperation with the Fish and Wildlife Service, were interrupted by the war and have not been resumed there. However, the prepoisoning technique has been employed successfully since the war in the Pacific Northwest.

The procedure at the Northern Rocky Mountain Station was to place about a tablespoon of poisoned bait (hulled sunflower seed treated with thallium sulfate) at 20-foot intervals over the seeding area a week before sowing the seed. Four experimental field trials of 10 to 50 acres each were made on cut-over and burned forest land in the western white pine type, seeding with western white pine. After 5 years, from 67 to 79 percent of the seeded spots on these areas were stocked. Subsequently a 97-acre tract was seeded as a reforestation job by CCC labor without the painstaking care exercised in the earlier experiments. After 5 years this tract showed 62 percent of its spots stocked. Some of the spot failures here were attributed to too-deep coverage of the seeds by careless workmen rather than to rodents. Other tests showed that treating the tree seeds with poison failed to give adequate rodent control where the area had not been prepoisoned. When pre-poisoning was used, treating the seed did not increase the stocking enough to justify the added costs.

Cost of the bait used in the prepoisoning was about 25 cents an acre, and the labor required to spread it was about 2 man-hours.