In the early 1900s the famed Austrian botanist Joseph Rock toured the Hawaiian archipelago cataloging native tree species. When he arrived at Auwahi, a swath of forest halfway up Haleakalā on Maui, he hit pay dirt. “Unpromising as it looks from the road, this forest is botanically one of the richest in the Territory,” Rock wrote in his authoritative tome, The Indigenous Trees of the Hawaiian Islands.

By his estimation, only one other region compared in terms of biodiversity: Pu‘uwa‘awa‘a on Hawai‘i Island. Neither of these was the lush, green rainforest one might expect. Rather, they were dryland thickets: tangled riots of shrubs, vines and hardwood trees adapted to life in the leeward rain shadow. These botanical treasure chests supported an abundance of species found nowhere else on Earth. And, threatened by the encroachment of cattle, they were in danger of disappearing.

Rock had a local guide at Auwahi: William Ainoa Kaiaokamalie, whom he photographed at the base of an enormous a‘e tree, six times the man’s height. From the a‘e, Kaiaokamalie pointed the way to the licorice-scented alani, the hōlei flush with creamy blossoms and the māhoe with its strange, twinned seeds that split open to reveal goggling scarlet eyeballs. Even then these trees were scarce, their names fading into the fog of memory. When Rock returned to Auwahi a few decades later, he reportedly fell to his knees and wept. Nothing remained of the once magnificent forest; cows had nibbled it to nubs.

Luckily, that is the beginning and not the end of this story.

Two dozen volunteers clamber out of four-wheel-drive trucks, tug on gloves and grab picks. It’s a warm and cloudless Saturday morning, but everyone has raincoats stuffed in their packs just in case. Weather can change quickly here on the southeastern shoulder of Haleakalā. From this vantage, four thousand feet up, the entirety of Maui’s central valley is visible. Kaho‘olawe hovers on the horizon. Farther south, the summits of Mauna Kea and Mauna Loa float on a lei of clouds. After taking in the view, the crew gathers for instructions. Group leaders carry ‘ō‘ō (digging sticks) and trays of dibble tubes, each slender tube holding a seedling.

As it turns out, something of Auwahi’s former majesty did survive: a few skeletal trees marooned here and there in a sea of pasture grass. For the past twenty years a volunteer brigade has been restoring the forest around them. Art Medeiros, the director of this workforce, explored Auwahi in the early 1990s as a research biologist for Haleakalā National Park. “The first time I came to Auwahi, I was so troubled by it,” he says. Hawai‘i’s dryland forests had been in steep decline since before Rock’s time. The giant birds—the flightless mao nalo that dispersed those big māhoe seeds—disappeared soon after the arrival of humans. Then rats, weeds and mosquitoes made inroads, claiming many casualties. Cattle and kikuyu grass delivered the killing blows. In the 1940s, ranchers planted the African grass to feed ranging herds. It carpeted the landscape in thick mats, suffocating seeds that tried to sprout.

Medeiros saw spinster trees that hadn’t reproduced in fifty, maybe a hundred years. He and his colleagues called the haunting landscape a “museum forest”—filled with artifacts but devoid of life. “It was tragic for me,” he says, “but it’s also where I learned my trees.” Even in its depleted state, Auwahi was home to nearly every native dryland forest species, minus a few found only on Kaua‘i.

In days past, Hawaiians came to Auwahi to harvest hōlei planks for canoe gunwales and roots for bright yellow dye. Carvers turned a‘e into resonant blocks of wood that sang when used to pound kapa (bark cloth). Healers foraged for medicinal herbs, and hula practitioners sought out perfumed maile vines and hala pepe, a tree whose branches they laid on the hula altar in honor of the goddess Kapo. According to ethnobotanist Isabella Abbott, “Diverse forests like Auwahi were the toolboxes of early Hawaiians. They are wahi pana, ‘sacred places.’”

Medeiros’ normal haunt was Kīpahulu, the rainforest around the corner. But a colleague challenged him to branch out: “The dry forest of Maui is legendary. You could really make a difference by finding out its status.” There was an obstacle, of course: Auwahi was outside the federal park’s purview, on private land belonging to Ulupalakua Ranch. Ranchers tend to view conservationists with skepticism if not hostility. Medeiros took a chance and approached the ranch’s owner, Pardee Erdman. “I asked Pardee if I could come on his ranch to look for endangered species —not really realizing that was a hot-button issue. He looked at me and almost sarcastically asked, ‘When you find these endangered species, what are you going to do?’ I said, ‘I’m going to tell you about them.’ And he said, ‘I look forward to hearing what you find. Here’s the keys to the ranch.’” This singular act of trust set a miracle in motion.

The damage had already been done by the time the Erdmans purchased Ulupalakua Ranch in 1963. Pardee and his son Sumner weren’t responsible for the forest’s demise, but they wanted to be good stewards. So in 1997, Medeiros began surveying the hillside for endangered species. He found them, including the rarest of the rare: one of only two alani trees left in the wild. Initially, he built small fences around individual trees to protect them from grazers. But he soon realized that he needed to think bigger: To save these trees, he would need to build an entire forest around them. “I didn’t know the word ‘restoration’ at the time, but that’s exactly what I wanted to do: re-create habitat, the processes of pollination and seed dispersal and germination. It was futuristic then, but it’s the way the world is going now.”

The Erdmans agreed and gave Medeiros ten acres to experiment with. He chose a spot rich with elder trees that was half rocky, half deep grass. It was guesswork from the start. Not much was known about Hawaiian dryland forest plants—except that they tended to be slow-growing, finicky and hard to propagate. At the time, Medeiros was teaching Hawaiian natural history at Maui Community College. After class one night, a man approached him with a lei and a request. “Be my kumu [teacher],” the man asked. His name was Mahealani Kaiaokamalie. He was the grandson of William Kaiaokamalie, and he wanted to help at Auwahi. His family’s kuleana (responsibility) to mālama (care for) that forest reached back many generations, he told Medeiros.

“We became dear friends,” Medeiros says. The men didn’t know whether it would be possible to restore the forest, but they were willing to try. When Medeiros mentioned that he wanted local hunters to be part of the fence-building effort, Kaiaokamalie called up his friends. At 4 a.m. a caravan of trucks arrived, their beds full of kiawe wood posts. Medeiros introduced himself truck by truck and led everyone up the mountain, where the men drove fence posts into the rocky ground.

Once the fence was in place, Medeiros sprayed the kikuyu grass—a mistake. He’d thought that the native seedbank would naturally germinate after he eliminated the pressure of grazers and smothering grass. Instead, weeds jumped in. He winces as if the memory causes physical pain. “Necessity is the mother of invention,” he says. “So I came up with two things. First, asking people for help. Second, a strategy for biotic resistance—the ability of the community to defend itself—and using native shrubs to do it.”

He reached out to Hawaiian plant nurseries and growers such as Anna Palomino, who provided a supply of olopua saplings and young ‘a‘ali‘i plants. An old Hawaiian proverb praises “the small, wind-resisting ‘a‘ali‘i of Pi‘iholo.” It’s a species known for its tenacity and a metaphor for a modest but powerful person. Distributing these hardy natives throughout the exclosure would prevent weeds from taking over. But ten acres was too big a garden to tend alone, so Medeiros recruited volunteers. This led to an epiphany. “So many people came,” he says. “It was amazing! Sometimes scientists think that people don’t care. Seeing how much they do care makes you unwilling to surrender or to take a step back.”

Before long the disheveled patch began to transform, like a CPR patient sputtering back to life. The ‘a‘ali‘i and other shrubs offered protection for more tentative species. Old trees began dropping seeds. “It was magic,” Medeiros says. “I started to see things I’d never seen before, like hala pepe seedlings in abundance. We found baby sandalwood and ‘aiea seedlings far from their parent trees.”

Today the exclosure’s fence marks a dramatic boundary between pasture and forest. Inside, the forest brims with life. Spindly hala pepe trees weave in the wind, dangling bushy mops of leaves and droopy chandeliers of orange fruits. A ball of maile—ripe with purple berries—blocks what might otherwise be a path. Beside it, a māhoe tree planted fifteen years ago also bears fruit.

Remarkably, the forest is now so dense that two dozen people are easily lost within it. The only sign of toiling volunteers is the shaking of leaves here and there and periodic shouts for more seedlings to plant. A sweet camaraderie builds over the workday, and strangers bond over rare Hawaiian plants. After a lunch break, Medeiros passes around chocolate chip cookies, which he bakes before every work trip.

Over the past two decades, volunteers and a few devoted employees have planted well over one hundred thousand plants here. Everyone relishes the opportunity to see, smell and nurture some of the planet’s rarest species. One of the project’s greatest strengths is its community support, particularly among Hawaiian lineal descendants of the area. Mahealani passed away not long ago, but other members of the family are fixtures. Mahealani’s nephew, Ainoa Kaiaokamalie, leans against the ‘ō‘ō he’s been using all day. “I feel responsibility for this place,” he says. He named his daughter Kala‘au—which translates literally as “the plants”—and snuck her up to work here when she was just three years old. Normally, volunteers need to be older and robust enough to navigate the remote and rugged terrain. But Kala‘au could handle it. She’s since made herself indispensable, greeting new volunteers at the start of the day, collecting signed liability waivers and offering tips on planting. Now ten, she can’t wait for Saturday workdays. “I’m stoked,” she beams.

By all measures, the Auwahi Forest Restoration Project is an enormous success. Two-thirds of the species now reproduce naturally; Medeiros says that he doesn’t plant seedlings now so much as release them, setting them free into their wild habitat. The flowering hōlei tree represents a particular triumph. It’s an endemic relative of plumeria, and its elegant, five-petaled blossoms release a perfume like that of their cousin’s, only wilder. “I told volunteers we’ll never see a lei of this in my lifetime,” says Medeiros. “Then one day they brought me one.” But that didn’t come close to topping the day they planted eight alani seedlings near Auwahi’s single kupuna (ancestor) tree. The species had perched on the edge of extinction for decades. Many people shed sweat and tears to coax the last two known specimens into producing seeds, then getting those seeds to germinate. When eight strong alani saplings were replanted in their natural habitat, a small but joyous crowd celebrated with Hawaiian chants and prayers.

It’s truly a case of “if you build it, they will come” at Auwahi. Hawaiian honey-creepers have flitted through, though the scarlet ‘apapane and ‘i‘iwi have yet to build nests here. Native insects and spiders have returned by the score. Hawaiian arachnid expert Rosemary Gillespie identified a species new to science at Auwahi, its only home. Tetragnatha albida, the white lady spider, hides during the day, camouflaged against the greenish-white lichen that covers many of the older trees. At night T. albida emerges to build webs among the branches. The forest’s rehabilitation has even altered its hydrology—soil within the exclosure captures rainwater more efficiently than in the neighboring pasture.

Twelve years ago Medeiros asked the Erdmans for more land. They gave him twenty-three acres, which became Auwahi II. That proved so successful he asked for a pie-in-the-sky number: 150 acres. They gave it to him. He fenced the entire area but has only started to restore the upper corner, Auwahi III. You can see all three sections on Google Maps: a trio of dark green patches laid on the landscape. Medeiros deliberately made them square; obviously man-made, they’re a testament to the potential of restoration ecology.

A project like this comes with no guarantees. Now that seeds and spiders have returned, so have hungry rats. Team Auwahi will have to devise ways to control rodents or watch their hard work waste away. This embattled forest might always need human aid, but from what Medeiros has witnessed over the past twenty years, that’s probably a good thing. The volunteer trips have birthed a new generation of ecologists. People from all backgrounds have made the trek up here, gotten dirt under their fingernails, maybe waited out a rainstorm under an ‘a‘ali‘i hedge and discovered a love for the dryland forest.

Medeiros won’t be here for the project’s final phase, when the trees reach maturity and unfurl fifty-foot-tall canopies like those Rock photographed. He doesn’t mind. The idea of Auwahi outliving him is a motivating force. “I used to say the forest was like a broken canoe,” he says. “I pulled it off the reef into deep water, and it started to run. It showed me that it still had life in it, and then it started to pull me! It pulled me to places I didn’t know could be reached.” HH