Silversword Fight

My boots crunch through thick hoarfrost as I hike uphill on a narrow trail, my collar turned up against a biting chill. The world is stretched below me in a blanket of pillowy pink clouds catching the dawn light. Beneath those clouds, the soft sands of Maui’s beaches will soon be beckoning to tourists; above the clouds soars 10,023-foot Haleakalā, a dormant shield volcano comprising most of the island. 

The Hawaiian alpine ecosystem is a land of extremes — surprisingly cold at night and mercilessly exposed by day. Plants and animals that call this place home balance on a thin line of survival. The line is getting even thinner for one of these plants: the Haleakalā silversword. As I pass one by the park’s visitor center, its namesake leaves bristle as if on the defensive against the threats it faces.

Sunny days like this are typical high on the mountain, but they weren’t always so common. In the past, the trade wind inversion, a weather phenomenon that traps clouds at low elevations and exposes high elevations to blazing sun, was regularly punctuated by intervals of clouds and rain. Current trends show significantly fewer breaks in the inversion, resulting in scant rainfall for the silverswords. 

“This can push them over a threshold,” said Paul Krushelnycky, an ecologist at University of Hawai'i-Mānoa who has studied silverswords since 2007. “If these current climate patterns continue, the silversword is going to have a really tough time.”

The silversword is the product of evolution in island isolation. Several million years ago, a California tarweed seed traveled 2,000 miles across the Pacific to Hawaii. This single species evolved into the “silversword alliance,” a group of more than 30 species endemic to Hawaii that range from scraggly shrubs to ground-clinging cushions.

Haleakalā silverswords — ‘āhinahina or “very gray” in Hawaiian — live only in a 2,500-acre area at the top of the Haleakalā volcano, a moonscape pocked by cinder cones and spattered with volcanic bombs. They have developed an adaptation toolkit to cope with this harsh environment: The fleshy leaves are coated with tiny silvery hairs to break the wind, prevent desiccation and collect cloud moisture.

At the end of its life, which may last over 90 years, the silversword grows a flower stalk upward of 6 feet tall. Hundreds of maroon flowers produce a luscious, pungent fragrance. Endemic winged pollinators swarm the blossoms, while damaging crawling insects are repelled by sticky hairs on the stalk. Because silverswords cannot self-pollinate, they must bloom synchronously and rely on pollinators for successful reproduction. After the plant dies, seeds are scattered by the wind, and a new cycle of life begins.

The silversword has shown itself to be one tough plant. Like many native Hawaiian species, it has faced threats brought from other parts of the world. During the 1700s, goats and cattle from Europe prospered by devouring native shrubbery. In Haleakalā’s spartan landscape, silverswords provided some of the only food for the plunderers.

In the early 1900s, Haleakalā started to attract adventurous tourists. Hikers gleefully tore up silverswords to roll them downhill or bring them back to the beach as triumphant proof they had reached the summit. Eager to look closely, they trundled around silverswords, unaware their steps crushed the delicate roots spread beneath the cinders. The plant was also turned into wedding garlands, and on at least one occasion, hundreds of silverswords adorned a parade float. 

Silversword populations had dropped dramatically by the 1920s and ’30s, dipping down to fewer than 20,000 plants in 1935. The Maui Chamber of Commerce, concerned about the possible extinction of the plant, petitioned the federal government to save the silversword. Park rangers tried to keep feral goats at bay and coached tourists in appropriate silversword etiquette. In the 1980s, the National Park Service strung fencing along the park’s boundary and eradicated thousands of goats.

Afterward scientists tracked a remarkable comeback, and for years the silversword was viewed as a conservation success story, rebounding to perhaps over 90,000 individual plants. But in the early 1990s, the species took another downward turn as days of fog and drizzle decreased. Researchers dove into climate studies but also focused on an up-and-coming threat: the Argentine ant. 

Hawaii is thought to have no native ants, but today over 60 ant species roam the islands. The Argentine ant was first documented in Haleakalā in 1967 and poses a significant threat to the park’s biodiversity and ecosystems. Haleakalā’s insects — including silversword pollinators such as ground-nesting yellow-faced bees — evolved without ant predation and are now being preyed upon by ants, which also compete with native critters over resources. Studies of the effect of ants on silversword pollination have been inconclusive, but some researchers think the ants will continue spreading into silversword habitat.

Today, 40,000 silverswords remain. Though this number may sound impressive, it represents a worrisome 60 percent decline since 1992, when the plant was listed as a threatened species. This is especially significant given the species’ limited range. To boost the population, Haleakalā’s botanist Patti Welton and horticulturist Michelle Osgood maintain a greenhouse of seedlings. In 2016, schoolchildren planted 1,200 of these silverswords in the park. 

This winter, Krushelnycky and park staff are planting silverswords in new locations to increase and diversify the distribution. “We want to see if wetter areas can help mitigate increasing temperatures and overall drying on top of the mountain,” he said.

As I hike home at the end of the day, clouds still shroud the bottom of the island. If scientific models prove correct, the line between clouds and sun will be moving downhill, leaving silverswords high and dry. I am worried about the future of this park’s iconic plant, but I also know that for centuries, the silversword has not only held on but rebounded when given the opportunity, and that gives me hope.