Collecting and Handling Seeds of Forest Trees

PAUL O. RUDOLF.

SOME 50 million acres in the United States (exclusive of Alaska and Hawaii) need to be planted to trees because they are not restocking naturally with desirable forest trees; because they are eroding, idle, or unprofitably used; because farmers' fields, animals, or buildings need protection from wind; and because the United States is going to need all the timber we can grow.

This tremendous undertaking will require more than 25 thousand tons of seeds of forest trees. To insure that this program gets the best possible start, we must apply the best knowledge we have about collecting, extracting, storing, and using the large quantities of forest tree seeds needed every year.

Although mote than 600 species of woody plants are useful for conservation planting in the United States, about 130 species make up the bulk of the seed trade. Furthermore, some 25 species, mostly conifers, account for about 90 percent of the area planted and seeded. Even this smallest group presents a variety of problems in collection, extraction, and handling.

THE COLLECTING of forest tree seeds in the United States is largely from wild stands, but increasing quantities are being gathered in plantations.

Beginning in the 1950's, some seed has been collected in seed production areas high-quality stands specially treated to foster heavy production.

Just being established, primarily in the South, are seed orchards made up of vegetatively propagated material representing selected superior trees. More and more of our seeds of forest trees are expected to come from these special stands and orchards.

Much of the supply in the United States is collected by private individuals, most of whom are independent operators. The greatest users of the seeds in this country, however, are the public forestry agencies, although there is a growing use by forest industries and commercial seed dealers.

Both the public and industrial agencies usually buy unextracted cones or fruits from the small private collectors.

The progressive collector of seeds of forest trees will scout out desirable collection areas in advance. He can get some early estimates at the time of spring flowering, but he should check the crops in the summer after the fruits are well developed, keeping in mind these points:

1. Confine collections wherever possible to trees above average in one or more of these qualities: Growth rate, stem form, crown and branching habit, resistance to damage, and seed production. Stands with a high proportion of superior trees are especially desirable for seed collections. Where areas of seed production or seed orchards are available, collect from them.

2. Obtain written permission of landowners before making any collections on their land.

3. Where available, utilize the regional tree seed-crop reporting services to locate collecting areas. In any event, estimate production from actual counts of fruits on representative trees or small sample plots well distributed over the collecting area.

4. Test for soundness of seeds in each locality and on individual trees before collection.

5. Label each sack, before it leaves the collecting ground, to show species; exact locality of collection (including approximate elevation); day, month, and year of collection; and any special merits of the parent stand (as "seed production area," superior stand, or "seed orchard").

Chances are best for getting seeds high in germinability and keeping qualities if they are collected when they are ripe and before they have suffered deterioration on the tree or on the ground.

Experienced collectors judge the ripeness of fruits by their fullness, size, color, degree of "milkiness" of the seeds, hardness of the seedcoat, their attractiveness to animals, or some combination of these factors. More precise indices are desirable.

For some pines and spruces, ripeness can be determined more accurately by the floatability of freshly picked cones in suitable test liquids, some of which are linseed oil for eastern white pine and blue spruce; SAE 20 motor oil for loblolly, longleaf, and slash pines; turpentine for white spruce; half linseed oil and half kerosene for Jeffrey and ponderosa pines; and kerosene for red and sugar pines.

For many tree species, the best time to collect is when the first seeds begin to fall naturally. Large-scale operations must begin sooner than that, however, to avoid substantial losses of good seed.

The best time for seed gathering varies for each species from season to season and place to place. As a guide, the general season is known for a great many species including some that can be collected in two seasons, as follows:

Spring: Aspens, cottonwoods, most elms, red maple, silver maple, poplars, and the willows.

Summer: Cherries, chokecherries, Douglas-firs, red maple, mulberries, Siberian pea-tree, and the plums.

Fall: Most ashes, beeches, most birches, boxelder, catalpas, cherries, Douglas-firs, firs, hickories, junipers, most larches, black locust, maples (except red and silver), Osage-orange, pecan, most pines, plums, spruces, sweetgum, sycamores, walnuts, white-cedars, and yellow-poplar.

. Winter: Some ashes, yellow birch, boxelder, catalpas, Osage-orange, black spruce, Norway spruce, sycamores, and walnuts.

Any season: Jack pine (except in the southern part of its range), lodgepole pine (except on the eastern side of the Cascade Mountains), Monterey pine, and sand pine.

Forest tree seeds commonly are gathered from standing trees. Collectors usually climb tall trees and detach the seeds or fruits by picking, cutting, or knocking them off. They handpick or flail off the seeds of small trees onto cloths from the ground or ladders.

Sometimes felled trees provide a cheap source, but the collector must gather seeds only from desirable trees cut after the fruits have begun to ripen.

The amount of seed produced per tree varies widely between species and from year to year. It is influenced also by the age, size, and health of the seed trees. Within any age or size class the dominant, widely spaced or open-grown trees usually produce the most seed if they receive adequate pollination. In good years a good seed tree may produce the following bushels of cones: Tamarack, 0.75; black spruce and eastern hemlock, 1; jack pine, ponderosa pine, red pine, and slash pine, 1 to 1.5; European larch and white spruce, 2; white pine, 5; and sugar pine, 5 to 7.

Some collectors gather squirrel-cut cones from the ground, but these fruits may not be adequately ripened. Collectors 30 or 40 years ago often obtained conifer cones from squirrel hoards in the Lake States and the West, but this is a rare practice today, except in the Pacific Northwest.

Fleshy fruits should not be crushed or dried more than superficially. Others should be spread out and dried partly before shipment. The fruits should be processed or extracted as soon as possible after collection.

SEEDS OF MANY TREE SPECIES Must be separated from the fruits and cleaned of fruit parts or debris to prevent spoilage, conserve space and weight, and facilitate handling and sowing.

They fall into three groups as concerns extraction:

1. Tree seeds readily extracted from dry fruits, such as cones (bald cypresses, cypresses, firs, larches, pines, spruces, white-cedars); conelike clusters (yellow-poplar); pods (Kentucky coffee-tree, honeylocust, locust); or capsules (aspens, cottonwoods, poplars, willows).

2. Dry fruits with seeds surrounded by a tightly adhering fruit wall, such as the nuts (chestnuts, oaks), and samaras (ashes, elms, maples, yellow-poplar).

3. Seeds of fleshy fruits, such as drupes (cherries, dogwoods, plums, walnuts), and multiple or collective fruits (mulberries, Osage-orange), and berrylike conelets (junipers).

Seeds of the second group are seldom extracted from the fruits because that is either unnecessary or very difficult. Those of the first and third groups are separated from the fruits by drying, threshing, tumbling, depulping, fanning, or sieving.

The simplest method of drying is to spread the fruits in shallow layers so that there is free circulation of air around each fruit. Where the climate is dry, drying may be done in the open. Where the climate is damp or the amount of fruit is great, it usually is done under a roof.

Protection from rodents and birds often is necessary to prevent serious seed losses during drying.

Some cones do not open readily and must be heated artificially in special kilns. These kilns provide the highest dry heat (usually between too' and 150 F.) that the seeds can stand without injury, and these predetermined safe limits must not be exceeded.

Two general types of kilns are used for extracting seeds from cones; simple convection and forced-air kilns. The first is the oldest, cheapest, and simplest to operate. The second is more complicated and expensive but more efficient.

Recommended temperatures and schedules in convection kilns for several pines are: Jack pine, 2 to 4 hours at 145 to 150 ; loblolly and slash pines, 6 to 48 hours (usually 8 to 10) at 120 ; longleaf pine, 12 to 72 hours at 120 ; ponderosa pine, 3 hours at 120 or less; red pine, 24 to 72 hours at 130 to 140 ; and Scotch pine, 5 to 24 hours at 130 In forced-air kilns, comparable schedules are 8 to 16 hours at 115 for longleaf pine, 5 hours at 170 for red pine, and 4 to 8 hours at 130 for Scotch pine.

Seed of the following genera and species usually are extracted by air or kiln drying: Aspens, bald cypresses, chestnuts, cottonwoods, cypresses, Douglas-firs, elms, hemlocks, incense-cedar, larches, the pines, poplars, sequoias, spruces, sweetgum, sycamores, thujas, white-cedars, and yellow-poplar. Normally kilns are necessary for the hard-to-open cones of these pines: Bishop, jack, knobcone, lodgepole, Monterey, pond, and sand.

After drying, the cones are tumbled in revolving screened cages or drums to shake out and separate the seeds.

The separation of seeds of many dry fruits from the bunches, pods, or capsules in which they grow requires flailing, treading under foot, or treatment in agricultural threshing machinery or special apparatus, such as a macerator, hammermill, or mixer.

Threshing or screening commonly is required to extract seeds of the alders, American beech, Kentucky coffeetree, firs, hickories, honeylocust, black locust, Siberian pea-tree, eastern red-bud, and walnut.