How Do You Solve a Problem Like Albizia?

The fast-growing invasive tree is a major hazard—and potentially a major resource
Story by Curt Sanburn. Photos by Michelle Mishina.

"I heard these things are called 'widow-makers,'" I say as I stop walking, crane my neck and look up. "... right?" I'm in a rainforest with conservationist JC Watson, deep in one of the gorges at the back of Honolulu's residential Mānoa valley.

We’re walking along a damp, asphalt access road. On either side of us, pale, smooth columns of albizia trees soar seventy-five, maybe a hundred feet up into the cloudy sky, where equally slender limbs, like joyous upraised arms, hold up wide, nearly horizontal canopies of feathery green. It’s a beautiful sight: Squint and we could be in the nave of Westminster Abbey. 

“Yeah,” Watson answers, “it’s called ‘sudden limb shear,’ or ‘sudden limb drop.’ These things grow so fast that the wood has no time to get dense. Even when they’re healthy, like these are, they can drop a massive, massive branch with no warning—they’ll just shear off a branch the size of a car. If it was windier today, this would not be a good place to be,” says the youthful 34-year-old, dressed in green hiking pants and a blue polo shirt. He points to all the albizia limbs and sticks littering the forest floor and picks up a two-foot-long, two-inch-thick stick. “If this fell from way up there … or that branch over there … dude, that’s gonna mess you up.”

I first noticed albizia (Falcataria moluccana, classified as an invasive weed tree by the state of Hawai’i) about thirty years ago, at Kalihiwai gulch on Kaua’i’s north shore, when I saw a whole cliffside festooned with those delicate, horizontal lines of green canopy, so exotic and downright elegant. Now I see them everywhere, scoring the Windward O’ahu pali, ballooning over the dwarf ‘ōhi’a forests of Puna, looming large and alone over Honolulu’s channelized streambeds. Before our eyes, on Central O’ahu’s vast and largely fallow plain where shaggy lawns of sugar cane once sprawled, invading albizia forests are colonizing whole  land quadrants with hovering clouds of trees, occluding the wide-open landscape.

In August 2014, Tropical Storm Iselle hit the Puna district of Hawai’i Island hard. Its sixty mile-per-hour winds toppled thousands of the flimsy, top-heavy albizias, whose long trunks and limbs blocked roads, ensnared power lines and crushed houses and cars. “The Tree that Ate Puna,” read a local headline. “Nothing crazier than the sound of intense wind followed by the sound of trees snapping and coming down hard and in slow motion,” a resident tweeted. The shocking damage-by-timber grabbed bureaucratic attention. Officials called albizia a statewide “menace.” With about twenty thousand acres of O’ahu and forty-three thousand acres of Hawai’i Island now infested, the tree is listed as a “High Risk Invasive” by the University of Hawai’i’s Hawai’i-Pacific Weed Risk Assessment. In 2017, the Hawai’i Invasive Species Council (HISC) funded a mapping project, still incomplete, to survey the extent of albizia infestation in the Islands. And just last year HISC, a state agency, adopted and published the state’s first plan to manage it: the twenty-one page Strategic Plan for the Control and Management of Albizia in Hawai’i, authored by John-Carl (JC) Watson.

Native to Papua New Guinea, Indonesia and the Solomon Islands, albizia was imported to Hawai’i in 1917 by botanist Joseph Rock, after the sandalwood trade and cattle grazing had denuded big lowland tracts of all the islands. Albizias—140,000 of them—were planted in the reforestation effort. Free from the naturally evolved enemies in their native range—fungi, seed-eaters and beetles—the thirsty trees found in Hawai’i’s lack of predators and plentiful rainfall a kind of heaven. The already fast-growing albizia has become, in the Islands, “maybe the fastest growing tree on the planet,” Watson tells me.

Not only are albizia prolific, they are also top-heavy, flimsy and prone to dropping thick limbs — and even entire trees — in moderate winds. Tropical Storm Iselle toppled entire groves in 2014, severing power lines and blocking roads.

Mosquitos finally drive us back to my car as a Mānoa rain begins. Watson lives in the valley with his wife and daughter. He tells me he has his own problems with albizia shoots popping up in his garden. They’re easy to pull out … at first, he says, but he had to pay to get rid of some thirty-footers. Watson grew up on O’ahu, attended Niu Valley Intermediate and Kaiser High schools, and got a degree in natural resources and environmental management from the University of Hawai’i in 2008. After that, he worked for pretty much everybody, he says, listing the US Fish and Wildlife Service, the National Tropical Botanical Garden, the private conservation group Pono Pacific and HISC. After publishing the albizia management plan early last year, Watson took on management of the Ko’olau Mountains Watershed Partnership, a consortium of landowners working to protect upland forests from invasive plant and animal species, particularly those that threaten the delicate forest biomechanics of collecting and storing rainwater on a tropical volcanic island. To do that, Watson and his hardy crews regularly helicopter up into one of a dozen remote landing areas and bushwhack their way to target zones, where they typically string fencing against pig and other ungulate infestations and eradicate invasive weeds like strawberry guava, paperbark, mule’s foot fern and albizia.

“If you’ve got a dense, healthy forest it’s really hard for albizia to get in,” he explains, detailing how its seeds need full sun to germinate. “But once they do get in around the peripheries, they gradually shade out the understory, or they’ll drop a big branch and then you’ve got a light gap and another tree … or twenty.

“So, we helicopter in to control each tree in place with herbicide. Take a fifty-foot tree with three-foot diameter trunk. You use a hatchet and notch the bark at about waist level, every six inches around the tree and then apply a half-milliliter of Milestone herbicide in there, in each notch. It makes a chemical girdle. It’s called incision-point application or IPA.” He describes how the trees, once treated, shed leaves then branches, until finally they “piece themselves down to the ground, to a trunk stump.” It can take five years, but it works and it’s cheap, Watson says: three dollars in herbicide cost versus anywhere between $10,000 and $20,000 to cut down and remove a single tree. He stresses that IPA is used only in remote areas, where limb falls don’t threaten anyone or anything. Elsewhere, when a tree poses a hazard and warrants removal, a certified arborist is required to “piece it down” one section at a time. 

Through raindrops on the car wind-shield, we study the foliage up on the walls of the valley. Albizia are everywhere. I ask Watson what message he most wants to get out there. “First of all,” he says, “these large-statured, beautiful trees aren’t what they seem. Albizia is a major pest. Let a field lie fallow for a year, you got twenty-foot trees growing in it, and you can’t just till those back in anymore.” Stream hydrology and flooding is another problem, he says. In 2004, albizia-debris snags dammed Mānoa stream, which diverted and flooded, causing $75 million in damage to the University of Hawai’i-Mānoa campus. 

So, what can we do? “Well, first you can pull ‘em up when they’re small,” Watson says, noting that albizia seedlings look like the common haole koa, a related invasive species in the pea family. “People can support the state’s Department of Land and Natural Resources in its effort to control albizia in the forests. And we can use the wood, whether it’s for construction, mulch or surfboards, something like that. Or burn it for power like they’re doing on Kaua’i —it’s called ‘green energy.’”

I mention recent UH Architecture School graduate Joey Valenti, who made news last year with his high-profile, design-build doctoral thesis project, a pod-like, four-hundred-square-foot prototype house made from specially engineered albizia lumber. It’s eye-catching on busy University Avenue in Honolulu, tucked under a monkeypod tree at the architecture school. 

Recognizing the need for affordable housing, Joey Valenti designed and built Lika House from albizia wood while pursuing an architecture degree at the University of Hawai‘i.

“It looks real good,” Watson says of the hut. “It’s culturally appropriate, and using albizia lumber to help with our housing crisis is a beautiful thing. If we can turn these big invasive trees into transitional housing, that’s cool! Joey can design it any way he wants to—he’s an architecture student—but his innovations in laminating the wood so that it can be load-bearing … that’s cutting edge.”

Minus the thatch, “Lika House” looks like a bulbous Melanesian longhouse—or a small, upside-down version of Noah’s Ark, with hundreds of lapstrake-style, fixed wood louvers running between the big arches, or ribs, of its “hull.” The structure imparts a real sense of architectural myth-making and adventure: It’s ready to sail us all back to the future, to a new age of sacred woodwork. Except for the steel and aluminum ground anchors and fasteners, the warm, golden edifice is nothing but albizia wood.

Designer and builder Joey Valenti meets me outside his ark on a warm August afternoon. We gaze up into the open interior with its raised floor (to keep it cool and flood-proof) and its loft, tucked under the vaulted ceiling. The topmost part of the roof is rigged with a removable, fitted waterproof tarp for rain. The airy louvers comprise the structure’s only skin and express Hawai’i’s enduring “No need!” cultural creed as seductively as anything; the arches, creating roof and walls in one system, are an age-old efficiency.

Completed in early 2018, Lika House was “an academic exercise designed to push the envelope of design,” Valenti says, “and the opportunity to prove albizia’s viability as a readily available construction material for Hawai’i’s housing crisis.” He spent a lot of time stress-testing the wood and innovating. Lika House’s three-inch-thick, laminated arches and joists made from three glued layers of one-inch albizia boards, with joints custom-spliced for extra strength. The wood was scoured from all over the island, milled in Waimānalo and pre-assembled in Wahiawā. 

In hindsight, Valenti admits that he and his team of engineers, professors and fellow students actually overbuilt the prototype: “We’ve proven that this structure is far beyond what’s required when using albizia as a material for building,” he says. “We also found that even simple dimensional albizia [that is, lumber milled to standard lengths and widths] has the strength properties to meet building codes for timber construction.”

The total cost to produce Lika House reached over $80,000, Valenti estimates. Funds were raised from various state and federal agencies and university departments as well as in-kind contributions from several local businesses. “A prototype is always the most expensive,” Valenti avers, “because you’re doing all the research and development, and it takes a lot of time to get everything right. Now that we have it down, the costs will be significantly reduced.” Later in 2019, the architect reports, Lika will be made available as a prefab kit house. I ask him how his work fits into Watson’s HISC plan to eradicate albizia, which includes finding sustainable uses for the weed.

“I’m glad you asked,” Valenti says. “That’s our intention—incentivizing removal and eradication programs. A healthy native forest is vital to everyone. With Lika House—or The Albizia Project, as we called it—the first question people ask us is, ‘Are you thinking about the long-term impact?’ And to me, the long-term impact is that we’re going to eradicate this stuff. Short term, we’re demonstrating that there is some practical use for albizia. Maybe we can house people for a while. But yeah, there’s a fine line there between recycling what you have and starting a new industry that might encourage people to start growing the stuff—that’s what we don’t want.”

Later in 2019 Lika will be made available as a prefab kit house. “To me, the long-term impact is that we’re going to eradicate
this stuff,” says Valenti. “Short term, we’re demonstrating that there is some practical use for albizia.”

Watson is in the vanguard of men and women who dedicate themselves to defending and healing Hawai’i’s native forests and grasslands—ecosystems that have suffered more species extinctions than most places. I turn the tape recorder back on because I need his help: I’m a Darwinist when it comes to natural selection, a reluctant believer in bio-logic, that stronger plants and animals will adapt and win—despite what that means for Hawai’i’s tender and heartbreakingly beautiful biota. Foreign albizias will prevail. Foreign mosquitoes and foreign microbes will vanquish our forest birds. And Hawai’i will change, is changing, irrevocably. I run quickly through a laundry list of campaigns to defend plants, animals and habitats in the Islands and eradicate destructive interlopers. “Isn’t it all a rear-guard action,” I ask Watson. “Is all this work in vain in the face of nature’s power?”

He is surprisingly respectful of my layman’s question. “It depends on the time scale,” he says. “If you’re talking geologic time, I mean, yeah, then nothing matters. But if we’re talking on a human time scale, I think a lot of efforts really do have positive results. One example is albizia. It was planted right here in Mānoa a hundred years ago. So it’s taken that long to get way up in the Ko’olau range at Waiawa, where we’re working. If we take out those thirty trees up there, we knock it back fifty to one hundred years. It really only takes a generation to grow a native forest, and if you maintain that effort for the duration, generation to generation, you can keep things on track—not in a man-over-nature way, but in a way of helping to keep the balance.” HH