Robert Cabin leaned with one hand against a tall but scraggly lama tree in a tiny, sloping patch of forest on the Ka`upulehu lava flow on the western slope of the island of Hawai`i.
The lama tree, known scientifically as Diospyros sandwicensis, has extremely hard ebony wood, so hard that native Hawaiians used it for house rafters. They also used the wood in medicine and placed it ceremonially in hula altars to represent Laka, the goddess of hula.
The tree is still fairly common to the leeward side of the Big Island, at least in isolated patches. The same cannot be said of nearly all the rest of the native plants that once thrived there, when vast tropical dry forests covered the leeward slopes of all the Hawaiian Islands.
Behind Cabin, down the parched landscape to the North Kona beach resorts nearly 2,000 feet below, spread an ecological desert, a barren carpet of black lava and sandy-colored alien grass dotted with single trees, many of them non-native.
“We’re standing among all kinds of species right on the edge of extinction,” said Cabin (pronounced CAY-bin), a plant ecologist with the U.S. Forest Service’s Institute of Pacific Islands Forestry in Hilo. The species he referred to were enclosed in a mere six-acre fenced site known as Ka`upulehu mauka.
It is a sobering thought: of those hundreds of thousands of acres of former dryland forest, only a few small “islands” of trees like this one remain. Many of the islands are slowly degrading as an ocean of alien animals and plants, and the rogue fires that come with them, constantly batter their shores.
But at this site, within earshot of the swish of cars and trucks speeding past on the island’s Belt Road between Kailua and Waimea, Cabin and others have found reason for hope. In just three years of weed-whacking, spraying with herbicide, and other sun-baked toil, they’ve seen signs that the forest – with a little help – can restore itself. Native tree seedlings, shrubs, and vines are rising anew out of the shallow soil and rough a`a lava amid slumped, gray clumps of the African bunch grass known as fountain grass (Pennisetum setaceum).
“I’m continually amazed at how many natives are popping up here and there, regenerating on their own,” Cabin said as he trudged over the lava pointing at what to the untrained eye looked like ordinary plants.
But what is happening at Ka`upulehu mauka is anything but ordinary. In the past five years, the site has emerged as an important research and demonstration project aimed at reclaiming Hawai`i’s degraded dry forests, one of the islands’ most culturally important and critically endangered habitats.
Fate of the Dry Forest
“This whole north Kona area, like the entire lowland dry side of all the islands, was among the most diverse forests in the state,” Cabin said as he led a journalist on a tour of the site in June. “People focus on the rain forest all the time, but there was much higher diversity here.”
The dry forests of Hawai`i get only about 20 inches of rain a year, while rain forests generally get about 10 times that much.
What happened to the native dry forests is a common story in Hawai`i and elsewhere in the tropics: they’ve succumbed to a modern-day crescendo of destruction that began with the original human settlement and built with Western contact, large-scale ranching, and a rising tide of development. In Hawai`i’s case, throw in decades of habitat degradation by non-native hooved animals.
“What’s left today are these tiny little fragments of dry forest, and we’re standing in one of the best in the state,” Cabin said. “It’s tiny — six acres. It’s just this little bread crumb of what was.”
About 40 percent of Hawai`i’s rain forests are gone, but the state’s dry forests have been reduced by 90 percent from what was originally found in the islands, said Marie Bruegmann, a biologist with the U.S. Fish and Wildlife Service (USFWS), in Honolulu.
In the face of these dire facts, Cabin, Bruegmann, and other members of an alliance known as the North Kona Dry Forest Working Group have launched an effort to restore at least some of Hawai`i’s dry forests. Their tools: research, education, and demonstration.
The group is an informal partnership of state and federal agencies, non-government organizations, botanical gardens, and native Hawaiian and other volunteers. Among the leaders are the USFWS, Hawai`i Forest Industry Association, Kamehameha Schools/Bishop Estate, and local residents Michael Tomich and Hannah Springer, a trustee of the Office of Hawaiian Affairs whose family has lived in the area for generations. Lisa Hadway, a postdoctoral research fellow at the National Tropical Botanical Garden (NTBG) who does field work with Cabin, was recently appointed coordinator.
The group believes that dozens of endangered and rare species, mainly plants, can recover in this area once the overall structure of the forest is restored. Ka`upulehu mauka still supports small populations of the endangered kauila (Colubrina oppositifolia), uhiuhi (Caesalpinia kavaiensis), aupaka (Isodendrion pyrifolium), `aiea (Nothocestrum breviflorum), koki`o (Kokia drynarioides), and hala pepe (Pleomele hawaiiensis).
With funding from various sources, the group is planting hundreds of nursery-raised seedlings of these and other endangered dry forest species among the naturally regenerating plants. In July, the Fish and Wildlife Service awarded the group $72,000 to boost the effort. In part, the agency hopes to provide habitat for the endangered Blackburn’s sphinx moth (Manduca blackburni), the state’s largest native insect.
The Site and Its Foes
“There’s the enemy right there,” Cabin said. “Goats.”
At the uppermost edge of Ka`upulehu mauka, just beyond the fence, a half-dozen black goats looked up as Cabin emerge from a clump of trees. They darted over a ridge and out of view. The fence is a key in what allows Ka`upulehu mauka to be Hawai`i’s most active laboratory for dryland forest conservation biology.
Shortly after the working group formed in 1993, members began to consider a site for the first demonstration project. Using a battery of criteria, they narrowed the choices to Ka`upulehu mauka and a site in Pu`uwa`awa`a.
They chose Ka`upulehu mauka partly because it had momentum for restoration. It had been fenced four decades earlier by the Territory of Hawai`i. Both the landowner, Bishop Estate, and its tenant, the NTBG, supported restoration. Finally, there was the matter of the “difficult politics” of Pu`uwa`awa`a, as one working group member delicately phrased it; this threw the decision in favor of Ka`upulehu mauka.
“It’s not entirely clear why they fenced it,” Cabin said. “Somebody just took it upon themselves to do it. Now this is one of the only dry forest pieces that’s been fenced for any length of time in the state.”
The fence saved Ka`upulehu mauka from the grazing, but luck played a large role in keeping the forest patch from burning down.
In the past few years, dozens of fires fueled by fountain grass have raged across the North Kona slopes, taking with them many of the last few fragments of dry forest.
Researchers believe that fires of the past were rare, and that most were probably ignited by lava. Without the fountain grass of today, those fires that did occur probably were quite localized. So by and large native plant species didn’t adapt to fire, and today they don’t come back from it easily, if at all.
“A really good forest down there burned a couple years ago last fall,” Cabin said, pointing down the slope and to the north. “There was a huge fire on this whole side of the island. It jumped the highway in several places and burned a lot of the last pieces left.”
Ka`upulehu mauka was spared because it borders an 1801 lava flow that served as a natural firebreak. The site itself was rife with fountain grass until 1996, when Cabin and his colleagues began a campaign to wrest it out.
Fences Aren’t Enough
In research published last April in the scientific journal Conservation Biology, Cabin and co-workers discussed the role of fountain grass in blocking dry forest regeneration. Their conclusion: In contrast to what many previously believed, the forest needs a helping hand in overcoming the choking effects of fountain grass and possibly also the damage done by rats.
“Removing ungulates is a necessary and critical first step, but it is not sufficient in itself,” Cabin said. “Putting up a fence and walking away won’t cut it. You’ve got to do more.” That “more” includes removing the fountain grass and poisoning the rats.
Joining Cabin and Hadway in the study were Stephen Weller and Ann Saki of the University of California at Irvine, David Lorence and Tim Flynn of the NTBG, and Darren Sandquist of Stanford University.
The study, begun in 1995, found almost no native canopy tree seedlings in the protected site – this, after more than 40 years of potential recovery time. Fountain grass and three species of rodents – the mouse, the black rat, and the Polynesian rat (all introduced) – had suppressed canopy tree regeneration.
The researchers discovered this by placing bait traps with rodenticide throughout the six-acre site. Then they painstakingly weed-whacked all the grass and sprayed each remaining clump six different times with a grass-specific herbicide.
By 1996, the grass cover was reduced 90 percent and the scientists observed a general decline in activity. A year later, canopy tree seedlings had taken hold in four out of 10 study plots in the preserve. A severe drought followed the next year, and experiments with drip-line irrigation began.
“We’re realizing now that it’s more complicated than we ever thought, and we’ve got to do more, depending on the weather,” he said.
After irrigation began, researchers have found 16 non-native plants new to the preserve, including milkweed and thistle. For nearly two years the researchers watched the native and non-native plants take advantage of the new conditions. But keeping in mind the value of the forest, they are now removing non-natives.
Doing What Works
In 1995, the working group selected a second patch of remnant dry forest for larger-scale restoration demonstration and experiments. The Bishop Estate owned this 70-acre patch, too. Known as Ka`upulehu makai, it extended just below Ka`upulehu mauka, separated only by the highway.
The tenant, Potomac Investment Associates, had begun restoration work there as part of mitigation for development elsewhere on the Kona coast. A small exclosure already existed in the area, but the working group built a fence around the entire site with funds from several sources.
The aim of the work at the makai site is to show that the dry forest can be protected from fire and restored with economical methods. Row after row of test plots were bulldozed, with some irrigated, some not; some outplanted with seedlings, some not; and some covered with shade cloth while others bake in full sun.
“We want to come up with coarser, more efficient, bigger-scale projects,” Cabin said as he walked through the plots. That might help the working group persuade landowners to restore forests on their land.
Despite seemingly insurmountable obstacles, group members remain optimistic. The bottom line, they emphasize, is that the dry forest can be restored.
“It’s a question of will,” Cabin said.
— William Allen
Volume 11, Number 3 September 2000
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