Archive: Hawai'i's Bioinvasion I: Life After Wilderness

(This series appeared in HIJ in 2001.)

Stretching along the Mana Road, about halfway up the windward slope of Mauna Kea, is a post-human landscape. For much of its length, the rugged jeep road follows a series of fences that mark the demarcation line between upland pastures and state- or federal-owned conservation land. The pastureland once occupied by forests of mamane and koa, has been turned into a graveyard of dead trees by years of cattle grazing. But now it’s not even very good for pasture. Much of it is choked with gorse: a prickly British shrub that literally grows needles on its needles.

Below the fenceline, the native koa-`ohi`a forest is also in trouble. Vast sections have been smothered with banana poka, a passion-fruit relative with long yellow fruit and beautiful purple-and pink flowers, which swarms over the crowns of the trees and covers whole forest canopies. The forest floor is often choked with waiwi (strawberry guava trees) and/or blackberry bushes. Wild pigs eat the poka and guava fruit, uproot native understory plants such as tree ferns, and defecate the poka and guava seeds, providing them with sunlight, fertilizer and freshly stirred soil. Imported game birds feast on the blackberries and spread them in much the same way. The dense growths of guava, poka and blackberry, in turn, form impenetrable tangles that protect the pigs and birds from hunters. It’s a coalition of creatures who were brought here by humans, but don’t need us anymore.

What’s happening on the Mana Road challenges our traditional notions of wilderness, ecology, and even evolution itself. When the National Wilderness System was set up, for instance, the first criteria of eligibility for inclusion in the system was roadlessness. The “trackless wilderness” has become a part of American mythology: once a challenge to settle, later a challenge to preserve. But the coalition of alien creatures at work on Mauna Kea doesn’t need roads. Pigs are natural bulldozers who can construct their own trails almost anywhere, bringing the hitchhiking seeds of invasive plants along in their hair and guts. The result is a weird landscape that can be entirely roadless, and yet by no means matches the conventional view of wilderness: a place where almost most nothing is as it was before the arrival of humans, but where humans seldom go. If humans were kept out entirely, the land would probably still go on changing, the native species would continue disappearing.

The situation along the Mana Road is not unique, unfortunately. All over Hawaii, non-native species are transforming the landscape. Hawaii Volcanoes National Park is under assault from myrica faya trees and Himalayan raspberry, glory bush and kahili ginger. Christmas berry and fountain grass spread through the forests of Puna and Ka`u. Roof rats leap like squirrels from branch to branch in the upland forests of Mauna Loa and Mauna Kea, where they feast on the eggs of endangered native birds. Almost weekly, another introduced species makes headlines: Caribbean frogs, stinging caterpillars, dengue fever microbes. A recent PBS program identified invasive species as a major agent of mass extinction – particularly in the Hawaiian Islands, which have more endangered species than any other state.

For the biologists and park managers charged with keeping Hawaii’s parks and conservation areas in their “natural” state, the battle against alien species forces hard decisions, including the use of bulldozers and pesticides. “Wildernesses” essentially become special farms, cultivated to produce crops of native birds, plants and insects.

The Gorse War

Dick Wass, who manages Hakalau Forest Wildlife Refuge, works on the front lines of the battle against invasive species. The refuge is home to at least six endangered Hawaiian birds, including the Akiapolo`au, Hawai‘i Creeper, Hawai‘i Akepa, koloa (Hawaiian duck), Hawaiian coot, and the recently re-introduced Nene (Hawaiian goose). Wass estimates that 95 percent of the refuge’s budget goes directly or indirectly toward the control of invasive species."

       “If it wasn’t for alien species, we wouldn’t have a job up here,” he maintains.

Driving up the Mana Road toward the refuge, he stops his SUV beside a patch of gorse to check the progress of some of his allies. Colonies of tiny orange gorse mites, introduced from the plant’s native Scotland, encase whole branches of a gorse plant in white webbing. Wass points to the tips of another branch: normally needle sharp; these instead seem blunt and hollowed out. They’re being attacked by gorse moth caterpillars. In addition to the moths and mites, a weevil has been introduced that eats the gorse seeds.

“The idea was to introduce several different species that attacked at different times of the year and attacked different parts [of the plants],” he explains.

The area around him looks like a battle zone. Huge swaths of former pastureland have been charred by fires set in an attempt to control the gorse. The blackened branches have simply grown more needles, or seeds in the ground have sprouted in new outbursts of prickly greenery. The various players in this upland drama – ranchers, the federal agencies, and the Department of Hawaiian Homelands – have tried herbicides, bulldozers, even goats. The gorse isn’t as healthy looking as it once was. But it’s far from defeated.

Ironically, it was ranchers who first introduced gorse, in an attempt to create living hedges in place of costly wire fencing. But the gorse quickly moved out of the fencerows and into the pastures. Cattle won’t touch it, while pigs using it for cover have spread into the pasturelands.

“People that have seen gorse in Britain – they can’t believe it,” says Wass. “They’ve never seen it grow as vigorously as they see it here.”

Until now, gorse’s various human opponents have fought their own battles by various methods. But Parker Ranch, the Nature Conservancy and others have recently embarked on an integrated gorse control program, hoping to coordinate efforts against the pest.

In the refuge itself, Wass says, “We’ve gone more toward the mechanical method. Earlier on, we were more into herbicide and fire. We’re just sort of learning as we go along.”

Wass and his work crews have tackled the gorse with bulldozers, scraping the tough roots out of the ground and shoving the plants into huge piles to rot.

“You’d think they’d explode into life, but they haven’t.” Wass says of the mounds. 

Chemical Pollution vs. Bio-pollution

But gorse isn’t the only invasive species problem that the refuge faces. Holly trees, planted for Christmas foliage, are spreading across the refuge, with the aid of birds that eat the berries. The former pastureland of the upper refuge is dotted with blackberry thickets. Thick layers of imported pasture grasses choke forest understory and hinder the sprouting of koa seeds, which are designed to be triggered by sunlight on bare soil when an old tree falls in the forest. Without the cattle that normally keep it in check, the grass also poses an increasing fire hazard. Kikuyu grass is especially virulent: evolved to survive the onslaughts of wildebeests, elephants and other African grazers, it is so hardy and fast-growing that if will even sprout atop wooden fenceposts. Whole fences on the refuge have been completely buried under grass.

Ironically, the grass has become an ally against the gorse. When the refuge’s bulldozers scrape the gorse away, the rapidly spreading grasses may inhibit the sprouting of gorse seeds in the scraped area.

Refuge employees and volunteers are fighting back against these invaders with a whole arsenal of specialized weapons. Conservation workers use a device that injects rifle shell casings full of herbicide into the bases of holly trees – a method that prevents herbicide from drifting onto native plants nearby. A weak solution of Roundup is sprayed onto blackberry patches. The banana poka problem has been reduced by hand-cutting the vines as well as by an introduced insect that has spread onto the refuge from elsewhere. The bugs strip the leaves off all but the top few feet of the vines, allowing sunlight to reach the leaves of the trees beneath. Ironically, the insects, like other biocontrols, first had to be used outside the refuge because of stringent rules about introducing alien species on federal wildlife preserves.

The refuge enlisted the help of local hunt clubs to cut the pig population on six “feral ungulate management units,” then erected miles of triple-galvanized fencing, at a cost of $25,000 per mile, to keep them out. In at least one section, a pig drive was held to chase some of the remaining pigs out through a gap in the fence before it was closed.

One of the worst problems the refuge faces is that of rats. Perhaps the ultimate weed species, rats can live almost anywhere and eat almost anything – including native bird eggs and nestlings, native plant seeds and native insects. The rats can even kill trees by eating the bark, and carry diseases such as leptospirosis. The refuge harbors at least three varieties of the rodent: the common Norway rat, the diminuitive Polynesian rat, and perhaps worst of all, the roof rat (also called the black rat), whose leaping and climbing abilities make it particularly suited to forest life.

“Rats are important not just for their effect on birds, but on the entire ecosystem,” believes biologist Bethany Woodworth of the U.S. Geological Survey’s Biological Resources Division, who helped conduct a rat control experiment on the refuge from 1994-1999. The scientists laid out two test plots – one in which rats went unmolested, and the other in which the rat population was reduced by using spring-loaded traps and bait stations. The result was a 60-90% decrease in the rat population, and a significant increase in the number of young birds from three common native species. But the cost per square kilometer of the rat-control program was $7,000 for the first year, and $2,000 annually thereafter, not including personnel – a prohibitive figure even for the 32,700-acre refuge, much less for the millions of acres of upland forest in other federal, state and private parcels.

Another USGS biologist is experimenting with hand-broadcasting or aerial broadcasting bait stations loaded with Diphacinone, which is approved for use in forested areas by Hawaii Department of Agriculture. If that proposal is ever implemented on a wide scale, it will probably draw fire from environmentalists concerned about dispersing pesticides through the rainforest. But the wildlife managers have to weigh any potential dangers from the rodenticide against the very real damage caused by the rodents. It’s a dilemma of chemical pollution versus bio-pollution.

Survival of Those that Fit

But perhaps the ultimate weapon against invasive species is a better understanding of how species themselves interact.

Had Darwin studied what was happening in the Hawaiian Islands, he might have reached a somewhat different understanding of evolution. The island’s original ecosystem was a prime example not so much of species competition, but of species cooperation, with scores of species specialized to support each other. Native birds, for instance, have developed special bills to reach the nectar in the flowers of particular plants, which in term rely on them for pollination. If you remove the bird, the plant dies; if you remove the plant, the bird dies. If the plants in the forest understory are healthy, then their shade protects against invasive weeds growing up. The whole system, then, both protects the individual species and is dependent upon them. “Survival of the fittest” becomes the survival of those that fit together.

A few species, such as the rats, seem to be in it mainly for themselves. But what is happening along the Mana Road is generally a team sport, fought by coalitions of species. Some of the coalitions are ancient: the Hawaiian rainforest, for instance, and. the pasture ecosystem that encompasses cows and grasses, grasshoppers and dung beetles. Other alliances, such as the pigs and poka, are new and unstable; no one knows what would eventually result if poka vines actually smothered the forest canopy, and the rotting trees brought the vines back to earth.

The decisive factor in some of these struggles may very well be which team humans decide to join.

At Hakalau, staff and volunteers are helping the forest defend itself from the invaders by helping the forest coalition to re-knit itself. Refuge staff and volunteers have planted 230,000 trees at Hakalau by since 1989. Most have been koa, but in recent years the refuge has also begun planting understory trees and plants as well, growing some seedlings in its own greenhouse system. Planting the trees in mauka-makai belts has created wildlife corridors to help endangered birds repopulate isolated stands of original forest. Planting stands in different years is allowing a multi-age forest to grow up, supporting different insects in different stages of the trees’ life cycle..

Along the way, the staff is learning more and more about how the coalition protects itself. One study discovered, for instance, that in established groves of trees, the temperature averaged three degrees warmer on winter nights – a critical factor in the refuge’s upper reaches, where light frosts killed many of the seedlings that staff and volunteers set out. So they began erecting thousands of “frost protection devices”: small barriers of black shade cloth that helped raise the microclimates around the seedlings by that that critical few degrees. Eventually, the mature stands will help -protect their own seedlings from the frost.

The cost of such efforts is steep; the refuge has an annual budget of around $900,000, bolstered by thousands of hours of volunteer labor. The staff is always on the lookout for volunteer groups to plant trees, gather koa seed, pull weeds, rip out old fence and kill holly. “If somebody has a group of 6-12 people who want to help, please give us a call,” Wass suggests. The refuge office can be reached at 933-6915.

Meanwhile, millions of acres of upland rainforest on state and private lands are enduring a similar onslaught, with little or no funds available for alien species control. A 1985 study found that less than 15% of the upland koa forest was still viable as a forest. That percentage is probably much smaller now.

The post-human landscape continues to advance.

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