Nature Out of Place

Biological Invasions In The Global Age

Jason Van Driesche, Roy Van Driesche

• Publisher: Island Press
• Year: 2013
• Print ISBN:
  9781559637589
  9781559637572
• eBook ISBN:
  9781610910958
• Topic: Biological Sciences
• Subtopic: Ecology
• Index: Biological Sciences

Though the forests are still green and the lakes full of water, an unending stream of invasions is changing many ecosystems around the world from productive, tightly integrated webs of native species to loose assemblages of stressed native species and aggressive invaders. The earth is becoming what author David Quammen has called a "planet of weeds."

Nature Out of Place brings this devastating but overlooked crisis to the forefront of public consciousness by offering a fascinating exploration of its causes and consequences, along with a thoughtful and practical consideration of what can be done about it. The father and son team of Jason and Roy Van Driesche offer a unique combination of narratives that highlight specific locations and problems along with comprehensive explanations of the underlying scientific and policy issues.

Chapters examine Hawaii, where introduced feral pigs are destroying the islands' native forests; zebra mussel invasion in the rivers of Ohio; the decades-long effort to eradicate an invasive weed on the Great Plains; and a story about the restoration of both ecological and human history in an urban natural area. In-depth background chapters explain topics ranging from how ecosystems become diverse, to the characteristics of effective invaders, to procedures and policies that can help prevent future invasions. The book ends with a number of specific suggestions for ways that individuals can help reduce the impacts of invasive species, and offers resources for further information.

By bringing the problem of invasive species to life for readers at all levels, Nature Out of Place will play an essential role in the vital effort to raise public awareness of this ongoing ecological crisis.

PART ONE

The Globalization of Nature

The Causes and Consequences
of Biological Invasions

CHAPTER I

From Endemic to Generic

Feral Pigs and the Destruction
of Hawaii’s Native Forests

The hallways of Los Angeles International Airport are lined with posters—offering glimpses of faraway places—Bangkok, Kathmandu, Paris—each billed as uniquely exotic. I was rushing to catch an 8:30 flight to Honolulu when one of the destination posters caught my eye. It showed a lush ravine lined with flowering trees and shrubs, with a series of knife-edged ridges in the distance. Hawai‘i. An exotic destination if there ever was one.

Or, more properly, an alien destination. It is unlikely that anything in that poster was native to the islands. The showiest of the flowering trees were African tuliptrees. The understory was mostly Indian kahili ginger. I was headed for a place that was largely no longer itself.

When the first Polynesian explorers arrived in the Hawaiian Islands about sixteen hundred years ago, upwards of 90 percent of the species they encountered were found nowhere else. This high level of endemism—the quality of belonging or being unique to a particular place—arguably made the islands the most biologically distinct place on the planet. These first Hawaiians converted some of the native lowland ecosystems to agriculture and caused the extinction of a number of species endemic to those habitats. However, because these people brought relatively few nonnative species with them on their 2,400-mile canoe voyage, the damage they did to Hawaii’s native ecosystems was mostly limited to the lowland areas where they lived and farmed. (One notable exception is that a number of upland species of flightless birds were driven to extinction at least in part through overhunting.) Their impacts were not substantially different from those of any other agricultural people who settled a place where farming did not previously dominate the landscape: they cleared land, hunted animals, and gathered plants. Beyond the margins of their fields, Hawai‘i remained largely Hawaiian.

The wholesale transformation of the undeveloped Hawaiian landscape gained speed only in the nineteenth century, when European explorers and settlers began to introduce one species after another to the islands in an attempt to make what they saw as a strangely depauperate and seemingly fragile environment a little more bountiful and robust. The response of the ecosystem to this constant influx of nonnative species made apparent some of the fundamental differences between an isolated island ecosystem such as Hawai‘i and a continental system elsewhere in the world. The islands’ ecological history created an inherent vulnerability to invasion by introduced species. Subsequent human-induced degradation further promoted the eventual devastation of the islands’ native communities by invaders. Species by species and acre by acre, native Hawai‘i has been disappearing since the moment it first appeared on a map.

When I got off the plane in Honolulu, the smell of the breeze across the open-air concourse was instantly familiar. It reminded me of Panama, where I’d lived for two years as a Peace Corps volunteer. Both the feel and the substance of the Hawaiian landscape were generically tropical. Apart from the mountains in the distance, there was nothing within miles to distinguish this from any other coastal city in any other tropical country in the world. Much of Hawai‘i—in fact, almost all of the inhabited portion of the state—is now as generic as a strip mall.

Below 2,000 feet elevation, nonnative species overwhelmingly dominate the Hawaiian landscape, and even at higher elevations many native species are losing ground. Overall, nearly 50 percent of the species found in the wild on the islands are introduced. A large and growing portion of the state—in 1999, about half of Hawaii’s land area—is no longer a native system that has been invaded by alien species; it is an alien system with a few native hangers-on. This process of transformation is creeping steadily upslope, each year moving a little higher into the remaining native forests.

Though many introduced species are implicated in the conversion of native systems to alien ones, there is a strong consensus among scientists and land managers that feral pigs, more than any other invader, are now responsible for initiating and driving this process further into the state’s remaining intact native forests. As direct agents of forest destruction, pigs root up the soil, trample native vegetation, and eat sensitive native species. But their indirect impacts are perhaps even more significant. By creating openings and rooting the soil, pigs open up forests to invasion by disturbance-adapted nonnative species—many of which are transported by the pigs themselves, as seeds in their droppings or in their coats.

I have come to the islands to document the many impacts of pigs on native forests, both directly and through the self-promoting complex of alien species that accompanies them. But I am also here to investigate the cultural and political implications of feral pig management, for this is an issue where the biological and the political are inseparable. Though the technology and the resources to control pigs are readily available, the issue of eradication—even in dedicated natural areas—is highly contentious. Whether any native forest still exists in Hawai‘i a century from now depends to a significant degree on how feral pigs are managed over the next couple of decades.

A Refuge for Native Hawai’i

It takes at least a full day to hike into Kipahulu Valley. The mountains and cliffs that ring this valley in the highlands of eastern Maui comprise some of the most difficult terrain on the islands, and no public trails lead in from the outside world. But very few people have ever gone in on foot anyway. Kipahulu is a closed scientific reserve, and those with permission to enter generally do so via helicopter. Such rugged terrain has kept out more than just hikers and explorers. In this section of Haleakala National Park is some of the highest-quality forest remaining in Hawai‘i—a forest where virtually everything is native, and almost all the historically recorded species still survive. This valley is the kind of place that has earned Hawai‘i a reputation among conservationists as one of the most beautiful and most unusual places on Earth.

But no place in Hawai‘i—not even Kipahulu—is entirely safe from invasion by nonnative species. The valley is crisscrossed by fences and laced with snares, the tools of a pig eradication campaign that began in the 1980s and that keeps the valley pig-free today. Even so, nearly a half century of pig presence prior to the eradication campaign allowed a number of nonnative plants to make inroads into the native vegetation, and the most frequent visitors to the valley today are Park Service weed control crews. It would now take, at most, only a decade or two of inattention even for Kipahulu, one of Hawaii’s most pristine places, to fall into irreversible degradation.

Kipahulu’s first systematic exploration came in 1945, when a pair of Park Service rangers ventured over from the Haleakala Crater to investigate the possibility of incorporating the valley into Haleakala National Park (at that time known as Hawai‘i National Park). Chief Ranger Gunnar Fagerlund and Ranger-in-Charge Frank Hjort hacked through thickets of uluhe fern and worked their way around cliffs on a five-day hike down to the coast. The forest was so dense and the terrain so rugged that even these experienced outdoorsmen covered only a mile or two a day. They reported seeing pigs just over the ridge from Haleakala Crater, but pig sign disappeared as they moved down into the valley. The valley was essentially free of alien plants all the way down to about 1,800 feet elevation. Fagerlund and Hjort described the valley as an ideal example of untouched “virgin wilderness” and strongly recommended that it be protected.

The Kipahulu Valley is one of the most isolated and pristine ecosystems left in the Hawaiian Islands. (Steve Anderson)

For the next twenty-two years, Kipahulu disappeared from the map. An occasional hiker might have ventured over the rim of the valley from Haleakala Crater and pig hunters probably worked the lower elevations, but there is little chance that anyone set foot in the heart of the valley until 1967, when a scientific expedition sponsored by The Nature Conservancy spent a month documenting the valley’s biological richness. The 1967 expedition found that, unfortunately, while human attention was turned elsewhere, nonnative animals had been moving in from above and below. From the 7,350-foot-high valley rim down to about 6,300 feet elevation, the landscape showed serious pig and goat damage, and alien plant species were establishing and spreading wherever rooting and browsing were most severe. At the bottom of the valley, the upper limit of heavy pig activity had moved from 1,800 feet to 2,500 feet. And perhaps most significant, pigs were present even at the valley’s once-pristine core. Though the expedition’s report noted that pig disturbance in the central valley “appears to be minimal as yet,” it emphasized in its recommendations that “immediate steps should be taken to reduce or eliminate the wild pig population.... Their damage to the vegetation is insidious but serious, and has in addition led to the establishment and spread of exotic plants in the valley.”

The 1967 report provided the impetus for The Nature Conservancy to purchase a portion of the valley and transfer it that same year to Haleakala National Park. (The state of Hawai‘i transferred ownership of the remainder of the valley to the Park Service in 1974.) The Park Service’s initial management strategy was simply to designate the area as a closed scientific reserve and allow no public access whatsoever. However, reports from park rangers of serious weed infestations along the route of the main 1967 trail prompted the Park Service to send a small expedition into the valley in 1976 to ascertain whether human disturbance had opened up the area to invasion by alien plants. The 1976 expedition found that weeds had indeed spread significantly in some areas and that lower section of the 1967 trail—from about 3,500 feet elevation downward—was dramatically degraded. But the human impact of the earlier expedition was not responsible for the difference at lower elevations. Pig sign was everywhere in the area below 3,500 feet, and what had been mostly intact forest understory in 1967 was now a vast pig wallow. “It is impossible to determine what the effects of the 1967 expedition were in this area,” the report stated, for “any effects have long since been masked by the effects of pigs.”

The members of the 1976 expedition were worried not only by the presence of pigs but also by the spread of the strawberry guava tree into the valley from below. They also highlighted the possibility (confirmed in recent years) that “pigs may play a role in its spread, both in carrying seeds and in removing competing vegetation.” Though earlier reports on the status of the valley had mentioned such a connection, the 1976 report was the first to note just how serious a threat the synergistic relationship between pigs and nonnative plants was to the integrity—and even the continued existence—of the native forest ecosystem of Kipahulu. Pigs were not only moving guava and other weeds up into the forest; the weeds were moving the pigs as well, for new infestations of guava trees served as higher-elevation food resources for pigs. “The current situation in the [lower] part of the valley ... should probably be described as an emergency,” the report concluded. In the strongest of language, it then urged that pigs be eliminated completely, before the pig-driven process of forest transformation degraded the valley beyond hope of recovery.

Nonnative feral pigs have devastated many of Hawaii’s remaining natural areas. (Jack Jeffrey Photography)

No action was taken, however, until after a 1982 study assessed pig population levels quantitatively and made explicit the consequences of failing to remove the pigs. Among other likely impacts of continued pig presence, the study predicted that strawberry guava stands would continue to replace native forest, the pool of alien species would increase, and water quality would decline. These concrete data persuaded Congress to provide funding for eliminating pigs, and as the 1982 study neared completion, plans for an eradication campaign began to take shape.

At the same time, the Park Service launched an interdisciplinary research project to document ecological changes in the valley as pigs were eliminated from the ecosystem. The valley was divided into three management units, and all but the lowest reach of the valley (the area already dominated by aliens) was fenced in with hog-proof wire. Permanent transects and study plots were established in the middle and upper reaches of the valley to monitor density and impacts of pigs, as well as the relative proportions of native versus nonnative vegetation as eradication progressed.

Pre-eradication population densities in the valley were 6.0 animals per square kilometer in the upper (more isolated) unit and 14.3 per square kilometer in the lower unit—both significantly lower than in many other natural areas. The Park Service team maintained an average of nearly 2,000 snares in the field for the forty-five months of the control program, ultimately the upper unit and 175 from the middle unit. By January of 1989, pig populations in both units had dropped to zero.

Four years after the last pig was killed, the Park Service team revisited two of the most heavily damaged study sites (one in the upper unit and one in the lower unit) of those that had been evaluated for pig impacts before control was initiated. In the upper unit site, 60 percent of the forest floor was bare ground and 40 percent was in native vegetation just before pig control. Four years after pig eradication, the forest floor in the upper unit was completely covered in native plants. In the middle unit site, 7 percent of the forest floor was bare ground, 3 percent was covered in native species, and 90 percent in alien grasses (all of which are significantly more tolerant of pig rooting than are native species) before the pig control program was initiated. Four years after pig eradication, 70 percent of the forest floor in the middle unit was covered in native species and 30 percent in alien grasses.

According to Steve Anderson, Haleakala National Park’s Natural Resources Program Manager, the difference between areas that showed complete recovery of native vegetation and those that did not was probably related directly to the intensity and duration of pig impacts. In the upper unit, pig invasion was recent enough and of low enough intensity that there remained rhizomes of native pohole ferns in the soil. Though pigs had introduced nonnative Hilo grass even into these most remote sites, the fern rhizomes in the soil allowed native vegetation to resprout and overtop the grass soon after pigs were eradicated. In the lower unit, however, pigs had been present long enough and at high enough densities that significant a reas were entirely devoid of native vegetation—even roots and rhizomes—when pig eradication began. As a consequence, nonnative species introduced by pigs were able to establish themselves in persistent pockets throughout the forest.

While the upper unit once again enjoys almost pure native cover, the fate of the lower unit remains uncertain. The difference in recovery between the upper and lower sites suggests that the postinvasion window of opportunity in which full recovery is possible may be quite short and that even relatively low pig densities can have significant effects on native vegetation. In fact, Steve Anderson is convinced that in the long run, there is no such thing as an acceptable pig population density in native Hawaiian forest, for even at very low population levels, pigs will decimate sensitive native plant populations, create disturbed areas in the forest, and bring in invasive weeds. “If you’re managing for a full complement of native species,” he said, “the only acceptable level is zero.”

Much of Kipahulu was cleared of pigs within the window of opportunity that allows for full recovery of native vegetation. But many of Hawaii’s other native forests have long since passed the point where the more sensitive native species are likely to recover to anything resembling preinvasion levels. For example, ongoing pig presence at the Big Island’s Hakalau Forest National Wildlife Refuge may be driving to extinction the very native bird species and rare plants that the refuge was established to protect. Though this forest is also considered one of Hawaii’s most ecologically valuable, the degradation it continues to suffer even under conservation management may prove irreversible. Whether Hakalau survives as a native forest community depends largely on how quickly the refuge is able to follow Haleakala’s model and eliminate pigs.

Pigs and Birds in the Hakalau Forest

Jack Jeffrey doesn’t like to spend much time in the office. He is a wildlife biologist, and there isn’t much of biological interest in the vicinity of the U.S. Fish and Wildlife Service office in Hilo. When we met in the parking lot at 7:00 in the morning to head up to Hakalau Forest National Wildlife Refuge—the 33,000-acre tract of rain forest on the windward side of the Big Island that Jack is charged to protect from pigs, rats, weeds, and a horde of other threats—he didn’t waste any time on administrative details. As soon as the rest of the expedition arrived, we jumped in his battered green Fish and Wildlife Service truck and headed up the road toward the refu...

Table of contents

• About Island Press
• Title Page
• Copyright Page
• Dedication
• Table of Contents
• Acknowledgements
• Preface
• Introduction
• PART ONE - The Globalization of Nature
• PART TWO - Saving Nature from Nature
• PART THREE - Going Local in the Global Age
• Conclusion
• APPENDIX A - Background Information on Biological Control in Natural Areas
• APPENDIX B - Species Mentioned in the Text
• Endnotes
• About the Authors
• Index
• Island Press Board of Directors