Collection Methods

Italic numbers in parentheses refer to Literature Cited.

Collection methods are largely hand methods because the desired wildland species do not grow in pure stands and the topography often limits use of mechanical equipment.

Grass Species

The seeds (caryopses) of grasses can often be collected by stripping. The stripper may be the collector's fingers or mechanical fingers on a truck-mounted or towed implement. The process consists of allowing the grass culms (stems) to collect between the fingers and the seeds to be scraped from the terminal inflorescence as the stripper moves forward. A simple seed stripper made from sheet metal and a gallon can may be a valuable tool for hand stripping (figures 1A and 1B).

Figure 1A. Seed collecting and threshing equipment: Simple seed stripper made from gallon can and sheet metal.	Figure 1B. Seed collecting and threshing equipment: Rubber-mat covered paddles for threshing.

The culms of the grass plant fit between the teeth of the stripper, and the inflorescences are pulled loose to drop into the container. In dense stands of annual grasses, a garden rake can be used to strip the seeds of some species. For large-scale mechanical harvesting, the seed stripper is a very inefficient way of collecting the seeds. A number of native grass species cannot be harvested satisfactorily by any of the conventional mechanical means, such as field combines, making it necessary to strip. A flow diagram for Thurber's needlegrass (Stipa thurberiana) seed collection is shown in figure 2. If wildland grass species occur in large enough stands or on topography that permits use of mechanical equipment, it is far more efficient to use a header or a forage harvester to collect the material for threshing than to attempt to strip the seeds. Headers are machines that clip the plants just under the seed head. Seeds are cured in piles and later threshed.

Forage harvesters can be used to chop mature grass stands. The chopped material is either cured for later threshing or the herbage and seeds are broad- cast together at time of planting. This can be a highly satisfactory technique in local areas where long distance transportation is not involved. The herbage provides a mulch to help establish the desired seedlings.

Grass fields can be repeatedly harvested the same growing season by simple modification of a standard combine (12). The cutter bar is covered with a section of split tubing or pipe so the grass stems are not cut, but slide under the combine. Before the grass stems slide under the covered cutter bar, extra large bats on the combine reel swat the seed heads, knocking mature seeds into the combine. Immature seeds remain in the seed heads and pass under the combine. The speed of the rotation of the reels should be increased four or five times over normal operating speeds for this system to work.

Many highly specialized harvesters, such as pneumatic-type strippers, bluegrass cylinder strippers, and suction seed reclaimers, are used commercially in the crop seed industry. If large-scale collection of a suitably abundant wild- land species is being contemplated, it may be worthwhile investigating this sophisticated equipment. A good source of information is Harmond et al. (9).

McKenzie (16) compiled the available literature on high-production grass seed collectors. This publication provides domestic and foreign sources of small combines and grass strippers. It also lists research organizations active in research and development of grass seed collection equipment and has a reference section for pertinent literature.

Broadleaf Herbaceous Species

The seeds of many herbaceous species can be collected by holding a tray or box under the inflorescence while shaking or flailing the mature seeds into the receptacle. For very small herbaceous annuals, the simplest method may be pulling the entire plant and bagging the material in paper sacks. Some herbaceous species have capsules or fruits that dehisce explosively. For these species, the entire inflorescence must be cut before maturity and allowed to dry on tarps or in mesh bags.

Collecting the entire plant is the only way to harvest seeds from spiny annuals such as Russian thistle (Salsola iberica), where seeds are produced axillarly over all of the plant (figure 3). When the entire plant is harvested, care must be taken to insure that the material dries without molding.

For herbaceous species that have spike-type inflorescences, pods can be stripped from the spike as with grasses. Lupines are a good example of a broad-leaf plant where stripping is possible. The pappused seeds (achenes) of many of the species of the Compositae (sunflower) family can be lightly brushed or swept into bags if the collector times dehiscence perfectly. Some of the Cornpositae have large heads for inflorescence that are subtended by armed bracts or spines. These heads can be clipped and bagged for later threshing.

Shrub Species

The seeds of many shrubby species can be collected by holding a tray or box under the out-stretched branches while flailing the bushes with a stick or paddle or by sweeping the arms across the upper branches to loosen the seeds, which then shower into the receptacle. For collecting bitterbrush seeds by hand, the Inyo tray was developed (20). It consists of an aluminum tray 20 inches long, 30 inches wide, and rounded at the bottom to a depth of 8 inches. A handle is inserted along the long axis. For limited collections, a cardboard box serves the same purpose as will baskets and canvas bags. A lightweight, 20-gallon barrel provides a ridged lip over which to bend shrub branches for removing fruits. This procedure is effective with spiny shrubs, such as desert peach, where the fruit must be physically stripped from the branches (figure 4).

Shrubby species with explosive capsules, such as Ceanothus, must have the capsules stripped before maturity and ripened in mesh bags or on tarps to avoid seed loss. Canvas or plastic sheeting spread on the ground to collect seeds loosened from branches is of limited value because of the time and difficulty required to spread the sheeting under low branches and over rocks.

Trees

The coniferous trees are the most important wildland species whose seed is extensively collected and sold in commerce. The specialized techniques for collecting and threshing conifer cones are explained in depth in the recent edition of the "Woody Plant Seed Manual" (23).

Species of Populus are important revegetation tree species in the Western United States. They are often propagated vegetatively rather than by seed. Seed collections require special techniques where branches with nearly mature fruits are cut and brought into a warm room or greenhouse and placed in water to allow the capsules to open.

Mechanical Harvesting of Tree Seeds

Mechanical tree shakers have been used to shake cones or fruits to the ground for later collection. Correct timing is necessary to limit damage to the trees.

Mechanical Harvesting of Shrub Seeds

Seeds of some semiherbaceous shrubs, such as fourwing saltbrush (Atriplex canescens), can be stripped by tractor-drawn seed strippers. Combines (combination of headers and thresher) have been used to harvest winterfat (Eurotia lanata) seeds (22). Field trials of vacuum harvesting, either vehicle mounted or a back-pack model, have shown promise for harvesting seeds of several western shrubs. Nord et al. (20) provide a comparison of hand and vacuum harvested bitterbrush seed collection efficiency and cost.

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