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By Root 2050 0

thousands of inhabited islands, almost all of whose inhabitants were chopping down trees, clearing gardens, burning firewood, building canoes, and using wood and rope for houses and other things. Yet, among all those islands, only three in the Hawaiian Archipelago, all of them much drier than Easter—the two islets of Necker and Nihoa, and the larger island of Niihau—even approach Easter in degree of deforestation. Nihoa still supports one species of large palm tree, and it is uncertain whether tiny Necker, with an area of barely forty acres, ever had trees. Why were Easter Islanders unique, or nearly so, in destroying every tree? The answer sometimes given, “because Easter’s palm and toromiro were very slow-growing,” fails to explain why at least 19 other tree or plant species related to or the same as species still widespread on East Polynesian islands were eliminated on Easter but not on other islands. I suspect that this question lies behind the reluctance of Easter Islanders themselves and of some scientists to accept that the islanders caused the deforestation, because that conclusion seems to imply that they were uniquely bad or improvident among Pacific peoples.

Barry Rolett and I were puzzled by that apparent uniqueness of Easter. Actually, it’s just part of a broader puzzling question: why degree of deforestation varies among Pacific islands in general. For example, Mangareva (to be discussed in the next chapter), most of the Cook and Austral Islands, and the leeward sides of the main Hawaiian and Fijian Islands were largely deforested, though not completely as in the case of Easter. The Societies and Marquesas, and the windward sides of the main Hawaiian and Fijian Islands, supported primary forests at higher elevation and a mixture of secondary forests, fernlands, and grasslands at low elevation. Tonga, Samoa, most of the Bismarcks and Solomons, and Makatea (the largest of the Tuamotus) remained largely forested. How can all that variation be explained?

Barry began by combing through the journals of early European explorers of the Pacific, to locate descriptions of what the islands looked like then. That enabled him to extract the degree of deforestation on 81 islands as first seen by Europeans—i.e., after centuries or millennia of impacts by native Pacific Islanders but before European impacts. For those same 81 islands, we then tabulated values of nine physical factors whose interisland variation we thought might contribute to explaining those different outcomes of deforestation. Some trends immediately became obvious to us when we just eyeballed the data, but we ground the data through many statistical analyses in order to be able to put numbers on the trends.

What Affects Deforestation on Pacific Islands?

Deforestation is more severe on:

dry islands than wet islands;

cold high-latitude islands than warm equatorial islands;

old volcanic islands than young volcanic islands;

islands without aerial ash fallout than islands with it;

islands far from Central Asia’s dust plume than islands near it;

islands without makatea than islands with it;

low islands than high islands;

remote islands than islands with near neighbors; and

small islands than big islands.

It turned out that all nine of the physical variables did contribute to the outcome (see the table above). Most important were variations in rainfall and latitude: dry islands, and cooler islands farther from the equator (at higher latitude), ended up more deforested than did wetter equatorial islands. That was as we had expected: the rate of plant growth and of seedling establishment increases with rainfall and with temperature. When one chops trees down in a wet hot place like the New Guinea lowlands, within a year new trees 20 feet tall have sprung up on the site, but tree growth is much slower in a cold dry desert. Hence regrowth can keep pace with moderate rates of cutting trees on wet hot islands, leaving the island in a steady state of being largely tree-covered.

Three other variables—island age, ash fallout, and dust fallout—had effects