August 2005 2400 0524–2331-MTDC
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Improved Whitebark Pine Seed Scarifier

Andy Trent, Project Leader;
Tyler Kuhn, Mechanical Engineer;
Karen Burr, Horticulturist, Coeur d’Alene Nursery

Nurseries scarify (nick or sand) whitebark pine seed to make it more likely to germinate. The U.S. Department of Agriculture Forest Service, Missoula Technology and Development Center (MTDC) has developed a new scarifier (figure 1) that lightly sands whitebark pine seed.

Image of four canisters (two with lids and two without) sitting on what looks like a scale.
Figure 1—The new sanding scarifier
for whitebark pine seed. The seeds
swirl across sandpaper lining each
of the four cans.

  • Whitebark pine seeds need to be scarified (nicked or sanded) to increase their germination rate.

  • Nicking seed by hand is tedious and somewhat dangerous.

  • The original scarifier developed by MTDC had problems.

  • A new scarifier appears to be just as effective, more reliable, less expensive, and requires almost no attention by the operator, a big labor savings.

The new scarifier can handle all sizes and shapes of seed, is more reliable, and doesn't have to be tended while it is operating, all big improvements over the original scarifier developed by MTDC. For information about the original scarifier, see the tech tip Whitebark Pine Seed Scarifier (0224–2332–MTDC, /eng/t-d.php?link=pubs). Before these scarifiers were invented, nursery workers used scalpels to nick the seed by hand (figure 2). Workers could nick no more than 400 seeds an hour and sometimes nicked themselves rather than the seeds. The original MTDC scarifier (figure 3) could nick 1,500 seeds per hour, was easier for workers to use, and was safer than nicking seed by hand.

Image of a hand holding a scalpel which is being used to cut a pine seed into pieces.  Also in this image is a separate picture of a nicked pine seed which is missing a small portion of its outer layer.
Figure 2—A scalpel is used to nick
(scarify) whitebark pine seed by hand. The inset
photo shows a seed that was nicked by hand.

Image of several mechanical contraptions.  One unit, which is on the floor, has several dials and buttons on it.  The next unit looks table-like.  The third unit has a mainshaft, a container and several hoses protuding from it.
Figure 3—The original whitebark pine
scarifier developed by MTDC.

Whitebark pine seed is a favorite food of the grizzly bear, a threatened species protected by the Endangered Species Act. Whitebark pine has declined over the past century because of white pine blister rust, insect infestations, and fire suppression. Scarifiers should reduce the cost of growing whitebark pine seedlings, allowing more whitebark pines to be planted.

Problems with the Original Scarifier

Whitebark pine seeds vary considerably in size and shape. During a production run of whitebark pine seed at the Forest Service's Coeur d'Alene Nursery in 2003, the original scarifier ran into problems nicking very round large seeds. Those seeds were not being nicked deeply enough or were not being nicked at all. The original scarifier also had to be repaired periodically.

Nursery personnel suggested another method of scarification: sanding the seed. Researchers who had studied whitebark pine seed found they could improve germination percentages by swirling small lots of seed in a can lined with sandpaper. This method is different than nicking, but the seedcoat gets scraped or sanded enough to help the seed germinate.

New Prototype Whitebark Pine Seed Scarifier

MTDC developed a new prototype whitebark pine seed scarifier that swirls the seeds in sandpaper-lined cans. Four 5-pound coffee cans, lined with 60-grit sandpaper, are attached to an 18-inch-diameter disk. An electric motor rotates the disk, while a chain-and-sprocket system keeps the orientation of the cans fixed relative to their starting position. The seed slides across the sandpaper, which is attached to the bottom and sides of the cans. A motor controller can adjust the speed of the disk's rotation from 0 to 140 revolutions per minute. Lids may be placed on the coffee cans to reduce the noise and keep the seeds from bouncing out.

If the new scarifier is proven effective, it will be much more efficient than nicking seed by hand or with a machine. Although a worker can feed about 1,500 whitebark pine seeds per hour into the original scarifier, doing so requires constantly feeding the machine. With the new scarifier, the operator can place seed into the cans, turn the machine on, and leave to handle other work. Even if it takes several hours to scarify the seed, the new scarifier will save labor, lowering production costs. Although each can could hold several thousand seeds, no more than several hundred at a time can be sanded effectively.

Test Procedures

Tests were conducted to determine how long the seeds need to be sanded and how fast the cans need to be rotated.

Speed Tests

A digital high-speed video camera recorded the motion of the seeds in the coffee cans while the disk was rotated at different speeds. The goal was to determine the speed that would move the seeds back and forth across the bottom of the can without sending them into the side so hard that the seeds could be damaged. Starting at 10 revolutions per minute, the speed was increased by 10 revolutions per minute up to 140 revolutions per minute. The high-speed video showed that 110 revolutions per minute provided the best motion to scarify the seed. This speed corresponds to a setting of 80 on the motor's speed controller.

Duration and Germination Tests

Once the scarifier's developers had determined the best rotational speed, they had to determine how long to sand the whitebark pine seeds. Tests were conducted with seed from the Coeur d'Alene Nursery. A sample from a lot of whitebark pine seed was stratified (soaked in running water for 48 hours, followed by 30 days of warm [70 degrees Fahrenheit] moist conditions, then 60 days of cold [34 degrees Fahrenheit] moist conditions). The seeds were scarified after they had been stratified. The seeds were placed in germination boxes (figure 4) that were put in an environmental chamber at about 70 degrees Fahrenheit. Comparison tests included:

Image of several evenly spaced seeds placed in a plastic dish.
Figure 4—Scarified seeds are placed in
germination boxes during testing.

Test Results

Figure 5 shows the results of the duration tests. The germination rate for the seed that was neither sanded nor nicked was 43 percent. Seed nicked by hand had a germination rate of 73 percent. Seed sanded for 3 hours had a germination rate of 72 percent, slightly lower than that of hand-nicked seed. The hand-nicked seed reached full germination in 8 days, while the sanded seeds took about 15 days.

One problem was solved during testing. During the 30-minute tests, some seeds got underneath the sandpaper, possibly damaging them. A Styrofoam ring was placed underneath the sandpaper near the perimeter of each can. This compensated for the uneven surfaces on the bottom of these cans. Seeds did not get underneath the sandpaper during the 120-, 180-, and 480-minute tests.

Image of a bar graph that illustrates the germination (percent) vs. sanding time (minutes) of seeds.  The graph illustrates that seeds nicked by hand had substantially higher germination rates compared to those that were neither nick sanded or nicked.  The maximum germination rate for sanding time was 180 minutes and the minimum germination rate in sanding time was 30 minutes.
Figure 5—Germination rates of seed sanded for up to
480 minutes (8 hours) compared to rates for seed that was
neither sanded nor nicked and seed that was nicked by hand.


MTDC has developed a new whitebark pine seed scarifier that appears to be nearly as effective as nicking seed by hand. The new scarifier uses four sandpaper-lined cans that are rotated by an electric motor to sand the seedcoat from whitebark pine seed. The new scarifier is far less complicated than the original scarifier developed by MTDC. The new scarifier costs $1,000 to manufacture, less than the original scarifier, and is more reliable. Fabrication drawings will be available from MTDC late in 2005.

One improvement that has been suggested is to incorporate a timer to stop the scarifier after a set period. This would prevent the seed from being sanded too long. Germination rates went down when seed was sanded for longer than 180 minutes (3 hours).

About the Authors

Andy Trent is a project engineer at MTDC. He received his bachelor's degree in mechanical engineering from Montana State University in 1989. Before coming to MTDC in 1996, he worked as a civilian engineer for the U.S. Navy. Andy works on projects in the nurseries and reforestation, forest health protection, and watershed, soil, and air programs.

Tyler Kuhn began working at MTDC as an intern in 2000. He received a bachelor's degree in mechanical engineering from Montana State University in 2001 and works for the center as a mechanical engineering technician.

Karen Burr is a horticulturist at the USDA Forest Service's Coeur d'Alene Nursery in Coeur d'Alene, ID, where she oversees seed and seedling quality activities. Formerly, she was a research plant physiologist at the Rocky Mountain Research Station in Flagstaff, AZ. She received her Ph.D. in horticulture from Colorado State University.

For additional information about the white bark pine seed scarifier, contact Andy Trent at MTDC.
Phone: 406–329–3912

The Forest Service, United States Department of Agriculture (USDA), has developed this information for the guidance of its employees, its contractors, and its cooperating Federal and State agencies, and is not responsible for the interpretation or use of this information by anyone except its own employees. The use of trade, firm, or corporation names in this document is for the information and convenience of the reader, and does not constitute an endorsement by the Department of any product or service to the exclusion of others that may be suitable.

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