Trees of Knowledge

Hawai‘i Island is home to a living laboratory for studying the world’s threatened tropical forests
Story by Alan D. McNarie. Photos by Andrew Richard Hara.

On a small plot of land near the base of Pu‘uwa‘awa‘a in North Kona, a rare tropical dry forest is regenerating itself. An endangered hala pepe, which resembles a pineapple crown perched on a broomstick, is shedding leaves: As it grows, the bottom leaves drop off, creating a layer of compost that retains water and deters weeds.

Uphill, an ‘a‘ali‘i is laden with hundreds of papery three-lobed seed pods; caught by the breeze, a ripe one helicopters away to start a new life. Near it, a pua kala—the native Hawaiian poppy—has already shed its white petals, and its prickly pods are opening as they dry, getting ready to spill black seeds smaller than grains of sand.

These plants had help. Most were grown in a greenhouse/garden complex nearby and were planted here after invasive species such as fountain grass had been cleared by foresters and community volunteers.

This forest restoration is only a small part of an immense, multi-organizational cooperative effort known as the Hawaii Experimental Tropical Forest, which is celebrating its tenth anniversary this year. Founded in 2007, HETF’s thirty-two thousand acres in Pu‘uwa‘awa‘a—as well as a twelve-thousand-acre rainforest and a fifty-five-acre education center in Laupāhoehoe—are cooperatively administered by the state Department of Fisheries and Wildlife and the US Forest Service. In addition to forest management and restoration projects, it’s home to dozens of research efforts by scientists from federal and state agencies, universities and nonprofits, with the help of local schools, community organizations and volunteers.

According to Elliot Parsons, the DOFAW forester who manages the Pu‘uwa‘awa‘a tract, HETF’s management plan has “eighty-plus objectives, including public access, hunting, endangered species conservation, fire protection and educational outreach.” One major goal is simply to learn more about Hawai‘i’s tropical forests in order to ensure their continued survival. And there’s an immense amount that remains to be learned. A forest is more than trees; it’s a vast, interactive process, a complex series of cooperative relationships. Every plant in the forest, for instance, has to propagate itself in some way—by dispersing its seeds on the wind, for example, like the ‘a‘ali‘i, or encasing those seeds in a tasty fruit so some animal will poop them out later. Flowering plants also need to be pollinated—and often they’re adapted to rely on a specific bird or insect to do that job. Evolution is survival not just of the fittest but of those that fit together.

But Hawai‘i’s forests are missing some parts. Its lava tubes still hold the bones of giant, extinct flightless geese, for instance, which may have eaten and dispersed certain fruits. The ‘alalā, the Hawaiian crow, currently surviving only in captivity, was also once a part of Pu‘uwa‘awa‘a’s forest; in fact, one section of the forest there was designated as a bird sanctuary, in part to ensure that the ‘alalā will someday have a habitat to return to. Right now, says Parsons, “We don’t know that much about the pollination strategies and the seed dispersion strategies. Some flowers look like they’re designed for birds that aren’t here anymore.”

Pollination and seed dispersal are only a couple of the many subjects scientists are investigating. What microclimates work best for which plants? How does water move in the forest? How can invasive species such as fountain grass, strawberry guava and feral pigs and sheep best be controlled? And the big question of the hour: Can rapid ‘ōhi‘a death be stopped?

The endemic ‘ōhi‘a tree, renowned for its scarlet lehua blossoms, is by far the predominant tree in Hawai‘i’s native forests—and rapid ‘ōhi‘a death, or ROD, has already killed hundreds of thousands of them on Hawai‘i Island. The disease is caused by a recently introduced and identified fungus that can kill a tree within days. The state is desperately trying to contain it while a cure is sought. That’s why everyone, from pig hunters to hula dancers, is being urged to observe a series of protocols, including cleaning and disinfecting their shoes and thoroughly washing their vehicles before and after entering any 
forest on the island.

The Hawaii Experimental Tropical Forest is comprised of two units, which serve as laboratories for scientists studying how to protect tropical forests from changing climate conditions. Pictured here, a cinder cone in the Pu‘uwa‘awa‘a tropical dry forest unit.

“We developed a lot of the sanitation protocols for ROD,” says Ricardo Lopez, HETF’s overall director. “We’re the ones who began the ROD Working Group. We’ve had a few hits in the Laupāhoehoe Forest. We took care of that really early.” Three HETF-affiliated scientists, Flint Hughes, G.B. Friday and Lisa Keith, have formed a rapid response team—the “ROD Squad”—to investigate reports of suspected cases. HETF scientists are studying whether some ‘ōhi‘a trees could be naturally resistant to the fungus.

But HETF isn’t just about solving specific problems such as ROD. It’s also engaged in pure research, including building up the most complete, detailed database ever made of any Hawaiian ecosystem. For that project, says Forest Service scientist Susan Cordell, she and her colleagues are using the same methods that other scientists are applying in forests from the Amazon to South Asia. As a result, it’s easy to compare data from those other areas. Every five years, every single tree and bush is visited in carefully mapped test plots. Detailed records are kept of how much each plant has grown, which plants have died, which sprouted and what new species, native or nonnative, have appeared, among other data. “We just finished, in 2016, our five-year re-census,” she says. “We’re still processing the data.”

One of the first things they discovered, Cordell says, was that “our forests are the least diverse tropical forest plots in the world.” That isn’t surprising, given that Hawai‘i is isolated by thousands of miles of ocean—or at least was, before ships and airplanes; it wasn’t easy for a plant to get here. But the breadth of the difference is pretty startling. An ancient continental tropical forest such as those of India, Cordell says, has as many as 1,200 species of trees. Laupāhoehoe’s rainforest has twenty-one. The dry forest of Pu‘uwa‘awa‘a, fifteen.

One focus of research in HETF is stopping Rapid ‘Ōhi‘a Death, a fungal disease decimating Hawai‘i Island’s ‘ōhi‘a. Developing sanitation protocols and propagating resistant trees are two approaches to battling the disease. Above, a lone tree in Pu‘uwa‘awa‘a.

Even more startling was this discovery: Although the number of tree species is relatively low, “the density of trees is almost the same as in other tropical forests,” Cordell says. In other words, just a handful of species have been shouldering the job of a forest: converting carbon dioxide, sunlight and a few minerals into about the same average biomass as hundreds of species do elsewhere in the tropics. And they’re doing it over a range of climates and altitudes. HETF’s forests reach from sea level to about six thousand feet, from rainforest in Laupāhoehoe to higher-altitude cloud forest to the dryland forests in the wind shadow of Mauna Loa.

How different climates affect the plants and how those climates are changing are also under study. Cordell believes climate change is “the biggest threat” to these forests. “We’re seeing a trend in increased nighttime temperature,” she says. That, in turn, “increases the plant’s need to respire carbon dioxide,” the most important gas implicated in global warming. “Carbon dioxide loss means that carbon dioxide is not available for growth.” Forest Service scientist Christian Giardina and Creighton Litton of the University of Hawai‘i at Mānoa are collaborating to study how temperature affects the forest’s ability to convert carbon dioxide into biomass.

Forester Elliott Parsons in the Nāpu‘u Conservation Project Native Plant Nursery, where some of the last remaining endemic plants in Hawai‘i are nurtured.

A warming climate threatens the forest in other ways. Warmer temperatures could allow mosquitoes to climb higher into the rainforest, for instance. Mosquitoes carry avian malaria, to which many native birds have no immunity, which in turn threatens the native plants those birds pollinate. To track these climatic changes, the scientists employ a dazzling array of tech, from a “climate tower” full of instruments in the Laupāhoehoe Forest to airborne LIDAR that senses the temperature and spectrographic variations among different types of trees. But their most valuable tool might be people—not just scientists but citizens. Pig hunters, for instance, share their expertise and observations, especially when it comes to eliminating invasive species. That’s ironic, because pigs are themselves highly invasive, rooting up native plants and spreading the seeds of other invasives such as strawberry guava. “It’s challenging to find common ground,” says Giardina, but “when you really talk with hunters, a great deal of their pleasure is being out there in the forest. One thing we do have in common is trying to get rid of invasive plants.” With the help of school and university groups, community organizations and other volunteers, the HETF team has planted over twenty-five thousand native plants over the past seven years. Some of those have literally been helped back from the brink of extinction. Take the koki‘o, for instance, an endangered native hibiscus with crimson, twisting petals. “There were maybe four of them in the wild,” says Parsons. “We’ve planted over a thousand of those trees.”

To understand how forests respond to a changing climate, HETF scientists monitor everything from water flow to temperature to light. Above, ‘ōhi‘a seedlings in the nursery.

Parsons recalls one particular Eagle Scout who solved a thorny problem. The first step in reforesting an area with native plants is to clear out invasives such as fountain grass, which has choked out huge tracts of forest and pasture in Kona. Early in the project, he says, “We cleared one area of fountain grass, and then we didn’t replant it immediately. We came back in about nine months. And the fountain grass was still dead, but it had been replaced by head-high bull thistle. It went from being difficult to clear to being a nightmare.” But the Scout volunteered to clear out the thistle as a merit badge project. Along with the badge, he should probably have gotten a Purple Heart. Since then Parsons replants immediately after clearing.

While Parsons and his volunteers plant trees, others help with the forest’s other denizens. A 2014 census of the birds in Pu‘uwa‘awa‘a, for instance, found native species that hadn’t been seen there in years. Still others work to restore the shoreline habitat in Kekaha Kai State Park on the coast below Pu‘uwa‘awa‘a.

All these projects are being conducted in accordance with an ancient Hawaiian concept. In pre-contact times, Hawaiians divided the land into ahupua‘a, sections that reached from the mountain peaks down to the sea—an entire watershed. Each ahupua‘a was self-sufficient, with most of the resources its residents needed. One “unique aspect” of Pu‘uwa‘awa‘a’s management plan, says Parsons, is that it follows the ahupua‘a system, preserving the entire watershed from the mist-shrouded uplands to the coast.

To track climate changes HETF scientists use an array of tech, from a “climate tower” full of instruments in the Laupāhoehoe wet forest unit (seen above) to airborne tools that sense the temperature and spectrographic variations among types of trees.

That’s not all that the scientists are learning from Native Hawaiians. HETF scientists and foresters have been consulting local kūpuna (elders) for their knowledge of traditional oli (chants) that record oral information about the areas where these forests grow, “the meaning of the Hawaiian names of the plants and the places,” says Lopez. The ahupua‘a model is part of an even bigger experiment, not just in biology or soil chemistry or stream hydrology, but in sociology and government administration, in forging coalitions to help the forest and finding new ways for all the stakeholders—scientists, pig hunters, Native Hawaiian gatherers, schoolchildren and, ultimately, anyone who drinks water that passed through the watershed or breathes the oxygen that the trees released. “We all have the same goal,” says Lopez. “We’re trying to restore the forest with the help of the community.” HH