HALEAKALĀ NATIONAL PARK — The Haleakalā silversword is a big flashy plant, attention-grabbing for its bulbous base of spiky leaves coated with silvery, shimmering hairs, and for the showy mantle of wine-red flowers that wrap its impressively tall stalk during its once-in-a-lifetime bloom.
In this national park's modest nursery, located just off the road that snakes to the 10,023-foot mountaintop, dozens of silverswords in black plastic starter pots are mini versions of those future selves. Arrayed on long metal tables, the squat little seedlings are watered and protected from the harshness of their native habitat until they are strong enough to return to the lunar landscape of the crater and high volcanic slopes of Haleakalā mountain. Here, on the island of Maui, Hawai'i, is the only place on Earth where the endemic plant is found.
If the outplanted seedlings survive to be large, sturdy plants in the wild, they will have one dramatic flowering season, their only shot at reproduction before dying.
But the Haleakalā silversword population is in steep decline. Against the pressures of drier climate and spread of a destructive ant, this mesh-sided nursery and its outplanting program are central to the park’s efforts to stave off its potential extinction.
“See, they’re making a little root here.” It’s a bright, sunny morning at the nursery and biologist Woody Mallinson, the park’s natural resources program manager, points out thread-like root strands that are driving straight down into the potted soil. “You can see this is ready to plant.”
The charismatic silversword, known to live for many decades as a silvery orb, even approaching centenarian ranks, has been losing population since 1990. It withers and dies, leaving its seeds to scatter, soon after casting a stalk skyward that is transformed for several weeks into its showy, once-in-a-lifetime bloom. So, no matter how old they get, the plants have only one chance for pollination and reproduction. Without the nursery protection for seedlings to thrive at least in their first vulnerable year, scientists believe the species may not make it.
“For sure, it’s the most studied plant in the park,” Mallinson says, surveying his silverswords and numerous pots of several other at-risk native plants. “Everything about this plant is amazing.”
“You look across the landscape and you see this silver spike contrasting against the red cinder. And then when it flowers, it can shoot up this five-foot inflorescence spike that’s covered in flowers — just super unique,” he says. And then there’s the scent. “It’s got just a nice, sweet fragrance if you’re standing downwind of a nice flowering population.”
Rough History
Haleakalā silversword — or ‘ahinahina, a reference to its silvery gray sheen — is one of around 30 endemic species from the “silversword alliance” believed to have descended from a California tarwood seed that found its way to the Hawaiian Islands millions of years ago. The alliance group varies from rosette plants to shrubs, woody trees, and vines located across the islands, including two high-altitude silverword cousins on Hawai’i island’s Mauna Kea and Mauna Loa mountaintops.
Silversword habitat extends between 7,000 and 10,000 feet on Haleakalā, ranging from inside the crater to parts of the rim and summit area. The tiny hairs on its leaves help trap moisture and protect the plant from the harsh sun. Hikers descending into the crater on the aptly named Sliding Sands Trail can see the plants rising like glimmering disco balls from the rocky terrain’s rust and brown hues. Signs strive to keep hikers on trails so they don't inadvertently trample the plants.
The slow-growing plant typically lives for 15 to 90 years before it flowers. The youngest flowering plants in research by Paul Krushelnycky, a University of Hawai’i ecologist and Haleakalā silversword expert, were in the 12-14-year age range.
The U.S. Fish and Wildlife Service listed it as a threatened plant under the Endangered Species Act in 1992 due to limited habitat and declining numbers. By then the silversword had weathered a rugged past, surviving human vandalism that was almost its undoing in the early 20th century: People couldn’t resist uprooting the plants for souvenirs or the apparent fun of rolling them down the mountainside, according to Park Service accounts. And it endured the indignation of being snack food for browsing cattle and feral goats that, like the humans, stomped on precarious seedlings.
The abuse caused Haleakalā silversword numbers to plunge to an estimated 11,500 to 18,000 individuals in 1935, said Krushelnycky. Then, the park pulled off what National Biological Service scientists in 1995 called “one of the most dramatic single species conservation success stories known.”
The rescue effort was straightforward: a crackdown on vandalism and a comeuppance for the munching animals, which were removed and fenced out of the park. With the perimeter fenced, silversword populations steadily increased in the mid-20th Century, park censuses showed. Park visitors were directed to stay on trails.
But that recovery didn’t last. The species again has steeply declined as Hawai'i has endured a drier, hotter climate and decreased rainfall. Its numbers dropped from a high estimated around 95,000 in 1991, when adjusting for counting error, to around 33,000 individuals in 2023, according to analysis by Krushelnycky, who has studied the plant for years.
“It’s getting drier and warmer on the top of the mountain. That does seem to be clearly linked to the negative population trend,” he told the Traveler.
Trade Wind Shifts
The drier conditions are tied to an abrupt uptick, starting around 1990, in the frequency of a common weather phenomenon known as the trade wind inversion, Krushelnycky and his colleagues reported in a 2016-published study. The inversion forms when dry, descending air that originates near the equator impedes rising air, capping vertical formation of the clouds to create a cloud layer below the mountain’s high elevations.
Visitors jostling for summit parking to view sunrises and sunsets are thus treated to a cloud layer sprawled like a bumpy, cottony sheet below them, while the rising or waning sun above the layer casts shadows across the cinder-covered slopes.
“When the trade wind inversion increased, that means anything above it — which is most of the silversword habitat — began experiencing more sunny days, less clouds, and drier conditions,” said Krushelnycky.
Normal breaks in the inversion allow silverswords to get rainfall, but the breaks have become less frequent, and although the plant is adapted to sunny, dry conditions, the moisture still is key to its early survival.
“You need to have a certain amount of moisture for seedlings just to make it through that first year. If you hit these long drought periods, you're not going to have a very good recruitment,” Mallinson explained.
Last year’s severe drought brought Hawai’i’s driest August in 35 years, according to NOAA. A report by the University of Hawai’i Sea Grant College Program stated it was the driest year on record for the island of Maui.
Teasing apart the complexities of the silversword’s decline, Krushelnycky found the plant faring better in some parts of its range than others, with apparently different levels of drought tolerance depending on habitat conditions.
“We've modeled the suitable habitat range, and that's where we're focusing all of our efforts,” for the outplantings, said Mallinson.
Is the Haleakalā Silversword Threatened or Endangered?
The Haleakalā Silversword was listed as a threatened plant under the Endangered Species Act in 1992 due to declining populations and dwindling habitat.
What is being done to save the species?
Scientists are working not only to grow more silversword plants that can be planted in Haleakalā National Park, but searching for places in the park that exhibit ideal conditions for the plants to thrive.
What is a trade wind inversion, and how do they harm the silverswords?
Trade wind inversions form when dry, descending air that originates near the equator impedes rising air, capping vertical formation of the clouds to create a cloud layer below the mountain’s high elevations. They impact silverswords by reducing the amount of moisture the plants need to flourish.
Kids in the Park
The park has outplanted 500 to 1,000 silversword seedlings annually since 2016, a Haleakalā spokesman said. Children from local schools have been key to the outplanting. Fourth graders come to learn about nature and stewardship and put silversword plants in the ground.
“A lot of the kids have never been to the top of the mountain before,” Mallinson said. “It's like the most incredible introduction to natural resources.” It also helps the short-handed park, which has trouble recruiting and retaining staff due to high housing costs on Maui, he said.
The kids’ handiwork is evident around the summit parking area and on adjacent slopes dotted with silverswords that shine brightly against the dark cinder terrain.
“It is important that the kids do it, so they have the history of the ‘ahinahina and so they connect with the plant,” said Mary Santa Maria, a Friends of Haleakalā board member and the group’s nursery coordinator. The friends group also has done outplanting, and hosts monthly nursery days for volunteers to pitch in with tasks like cleaning pots, weeding and seed gathering. Volunteers help remove invasive plants, and the group sponsors youth scholarships and programs focused on natural resource stewardship.
Biodiversity Emphasis
In all, the park hosts 36 plant species that are protected under the Endangered Species Act. Besides the threatened Haleakalā silversword, 21 federally listed endangered species are being grown in the nursery, from rare mint species to geraniums and lobeliads.
“There are more on this table today than there are of these in the wild,” Mallison says, pointing to a about 20 somewhat stringy, potted, Haleakalā schiedea plants. “It’s one of our more challenging plants to work with.” Besides drought, it is vulnerable in its cliff and subalpine habitat to hazards like rockslides, he explains.
When planting seedlings, the nursery keeps backup plants and seeds. “We want to always retain the genetics that we have, and we'll just produce more from those genetics” as needed, the biologist explains.
Saving species is part of a park emphasis on biodiversity to maintain a healthy native ecosystem. The silversword, for example, plays a key ecological role as host for several endemic insects. An intact ecosystem also reduces harmful runoff and is important to water quality for people downslope, scientists say.
Efforts to protect native plants also involve park staff helicoptering into rugged backcountry to check fence integrity and look for ungulates that might slip in and feral cats that disrupt ecosystems by preying on native birds and insects.
A crew heading out the following day would “follow up on fences that were replaced,” Mallinson said. “They're monitoring for weeds along those newly replaced fence lines. And they're also going to be doing invasive species control” to curtail destructive nonnative plants.
Aside from the climate shift, the silversword is vulnerable to incursion by the invasive Argentine ant. It preys on native yellow-face bees that are a major pollinator of the silversword and crucial to its reproduction.
The ant’s range likely is expanding with warming temperatures, researchers say. As far back as 1994, a report from the federal National Biological Service, a research agency during the Clinton administration, warned of “potentially catastrophic effects” to silverswords if the ant was unchecked.
“They're spreading. I see them in places they didn't used to be,” said Krushelnycky. “So far most of that doesn't really overlap much with the silversword distribution, but eventually it will.”
The ants, unlike ungulates, can’t be fenced out. They are “extremely difficult to control in natural areas and on a landscape scale,” Mallison said.
Rita Beamish, based in San Mateo, California, is National Parks Traveler's associate editor. A former Associated Press reporter in Los Angeles and Washington D.C., and former editor at The San Francisco Chronicle, she has covered a range of stories for the Traveler about climate change, wildlife, policy and environmental issues, and how the Trump administration has managed the National Park Service.
This project was made possible in part thank to the Park Foundation.
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