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ShareMar. 10, 1998 — TUCSON, AZ -- So few Mauna Kea silverswords remain in the natural population that years go by without a single plant flowering. Even if a plant does flower, the nearest silversword plant may be too far away for the two plants to exchange pollen.
The endangered plant will get a giant boost toward recovery in spring 1999 when thousands of seedlings are planted on the cinder-strewn slopes of the Hawaiian volcano Mauna Kea. The massive planting effort is spurred by University of Arizona biologists' discovery that previous restoration efforts, begun in 1973, had created a reintroduced population that was perilously inbred.
"Those reintroduced plants are all brothers, sisters, and cousins," Robert Robichaux, an associate professor of ecology and evolutionary biology at UA and director of the Hawaiian Silversword Foundation, said.
But injecting new vitality into the reintroduced population requires seeds from the dwindling natural population, now numbering fewer than 50 plants.
Two silverswords flowered last summer -- the first flowers in the natural population in four years. A team of biologists, including Robichaux, hand-pollinated the plants and collected their seeds. Plants from those seeds will substantially increase genetic diversity in the reintroduced silverswords, he said.
This summer, the team will search the remnant natural population for more flowering plants. If additional plants are in flower, the biologists will collect and transfer the pollen to generate more seeds for the outplanting program. And they will continue on foot and by helicopter to explore the remote, rugged slopes of the volcano to discover more isolated silverswords.
"We're really poised to make major progress now," Robichaux said. "We anticipate that we can probably get 15 to 20 thousand plants back on Mauna Kea in the next five years ... especially if additional plants flower."
1998 is an auspicious year for such improvements, he said. "It's both the 25th anniversary of the recovery effort for the Mauna Kea silversword and the 25th anniversary of the Endangered Species Act."
Robichaux and several colleagues will soon publish an account of the Mauna Kea silversword's recovery in the March/April 1998 issue of Endangered Species Bulletin. Coauthors are botanists Joan Canfield and Marie Bruegmann of the U.S. Fish and Wildlife Service, Frederick Warshauer of the U.S. Geological Survey and Elizabeth Friar of Rancho Santa Ana Botanic Garden. Robichaux and Friar, along with UA geneticist David Mount, published their research on the genetics of the plant in the October 1997 issue of Conservation Biology.
The rosettes of silverswords were once common on the slopes of Mauna Kea. However, sheep and other animals introduced to Hawaii grazed heavily on the plants. By the 1970s, only a small population of plants remained, tucked into an inaccessible gulch. For Hawaii to have only 50 silverswords would be equivalent to Arizona having only 50 saguaro cacti, Robichaux said.
"Plants used to be all over the slopes," he said. "Now you find plants growing only on cliff faces out of the reach of these browsing animals."
Although the state now has removed most of the sheep, the silversword's biology makes it unlikely that the plant will recover on its own, he said. An individual plant may live forty years before shooting up a six-foot stalk covered with hundreds of maroon daisy-like flowers. To form seeds, the flowers must receive pollen from another silversword plant, one that is not a close relative. Once the plant finishes flowering, it dies.
To ensure that the remaining plants in the natural population do not die without reproducing, a team of biologists watches the plants during the flowering season. As soon as one blooms, the scientists go to work.
"The plants grow in places where sheep can't get to them," Robichaux said, "which means it's a little challenging for people to get to them."
The biologists reach the plants by rappelling or by climbing up the cliff face. To collect the pollen, they gently knock the yellow grains off the plant onto a piece of waxed paper and carefully funnel them into a vial.
"Then we climb down the mountain to other plants," he said, "and, using a little brush, paint the pollen on the receptive flowers."
If no other silversword is blooming, the biologists store the pollen in a refrigerator and hope that another plant will soon come into flower. Part of the pollen is frozen so that it can be used the following year.
"It's very similar to sperm storage," he said.
The team of researchers collected 125,000 seeds from the two plants that were hand-pollinated last summer. The next step, Robichaux said, is to enrich the genetic diversity of the reintroduced silverswords by planting those seeds.
"We'll go over in April or May of next year and help with the first outplanting with the seeds from these new crosses," Robichaux said. "It'll be a long time before we know with certainty, but there's the opportunity now to make huge strides toward recovery."
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A photo of the Mauna Kea silversword is featured at the UA News Services Science & Research web site: http://science.opi.arizona.edu:591/science/
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