Volume 3, Issue 20 April/May 2006
Island Tales
Patrick Kirch holds the Class of 1954 Chair in Archaeology.
UC Berkeley professor Patrick Kirch spends a great deal of time digging in garbage heaps. The discarded bits of plants, animal bones, and other detritus that he discovers give him great insight into the people behind the rubbish. Kirch, an archaeologist, isn't after stinky, urban garbage though. His field research takes him to the Pacific Islands where trash heaps that are hundreds or thousands of years old hold clues about how humans may have impacted their environments, and vice versa.
"I use islands as models for how people and the environment dynamically interact over time scales of centuries and millennia," says Kirch, professor of anthropology and director of UC Berkeley's Oceanic Archaeology Laboratory.
Recently, Kirch and his colleagues pieced together a mystery about the ecosystem of Mangareva, a cluster of islands in southeastern Polynesia. And it's not an isolated story. What he found in Mangareva may help scientists determine what caused the ecological destruction of nearby Easter Island, as described in Jared Diamond's bestselling book, Collapse.
In this photo, Kirch records stratigraphy at the Mangareva site where the extinct bird bones were recovered. (courtesy the researcher)
Mangareva is a small group of volcanic islands surrounded by a barrier reef and lagoon system. Thousands of years ago, Mangareva had a thriving ecosystem. After the Polynesians settled there around 1,000 AD, things got ugly rather quickly. Islanders cut down the trees, stifling their own agriculture in the process and triggering a downward spiral that resulted in the degraded grass land that still exists today.
"It's basically a terminally ill ecosystem," Kirch says.
The question is how it got that way and why it didn't heal itself. For example, why didn't the trees ever grow back, even to this day? Are humans to blame? Kirch and his colleagues found the answer in the garbage, seabird bones long since picked clean by humans.
"I dig these up while being very careful to take note of the stratigraphic layers, the dating, and all of these pieces of data," he says. "Then I collaborate with natural scientists to identify what I find and what it may mean."
A large basalt "table" sits atop the Paepae, or floor of a house, at Atituiti Ruga, Mangareva. (Patrick Kirch photo)
For millions of years before humans arrived, large populations of seabirds roosted and nested on the islands. The researchers have discovered the bones of nearly two dozen species, most of which no longer exist in Mangareva. The seabirds, Kirch explains, fished in the surrounding ocean and returned to roost on the island, peppering the terrain with their droppings, an excellent source of nutrients for the soil. Then the settlers came.
"The birds were a wonderful food source for settlers and probably completely naive about human predation," Kirch says.
The settlers also brought with them a small species of rat that could have feasted on the fledglings, eggs, and vegetation. Within 200 years of settlement, the seabirds were gone. Meanwhile, logging had left the land bare and the soil lacked the nutrients necessary for regeneration. That in turn severely limited the Mangarevans' ability to grow crops. Kirch's research doesn't stop there though.
"I'm also interested in the reciprocal question," he says. "Once people change their environment, how do they adapt their social and cultural systems in response?"
The Mangarevans responded by becoming fishermen. With that as their only real natural resource left, the social importance of the fisherman became much greater there than anywhere else in Polynesia, Kirch says.
"The missionary accounts say that the fisherman, by withholding gifts of fish to the chief, could bring down the chief's power," he says. "This is an example of what happens when people come onto islands that have been isolated and undergoing natural evolution for millions of years."
A map depicting the islands where Kirch conducts research.
Mangareva is only one of many groups of islands that Kirch has explored in decades of fieldwork. He's currently principal investigator on a major cross-disciplinary project to study human ecodynamics in the Hawaiian ecosystem. The Hawaiian Biocomplexity Project is a collaboration with scientists from Stanford University, the University of Hawaii, University of Washington, University of Wisconsin, and University of California, Santa Barbara.
The researchers are studying how the Polynesian settlers, who arrived 1200 years ago, interacted with the pristine dryland areas of Maui and Hawaii. Already, the scientists have begun to discern how intense cultivation strained soil nutrients and that those early agricultural systems helped give rise to certain hierarchical, aggressive, and territorially expansive chiefdoms on the islands.
"Looking at the archaeology in these places is like a window into another world," Kirch says.