such locus is how population growth interacts with the environment. Archaeological evidence sketches a series of similar progressions across most of the Pacific that accord with mathematical models of demographic increase. Most every place in Remote Oceania, on the eve of European contact, had reached a near-maximum population density.71 Remote Oceania (Polynesia, Micronesia, and extreme eastern Melanesia) had much higher growth rates than Near Oceania (most of Melanesia and insular Southeast Asia) for several conditions and reasons. The first was a better disease environment, with no mosquitoes capable of carrying malaria east of the Solomons, due to the same dispersal difficulties encountered by other immigrants to remote islands. Next in importance were plentiful marine and terrestrial foods, at least initially; the lack of competing human inhabitants on arrival; and the cultural reasons for high fertility and voyaging already discussed.72
In every case, there is a familiar relationship between population increase, agricultural expansion and intensification, and environmental degradation. Equally strong is a corollary relationship between environmental stress and increasing social hierarchy. Kirch in On the Road of the Winds uses as his textbook case that of the island of Mangaia, in the southern Cook Islands, because of its extreme geological features and history of environmental and social disaster. It is an ovoid island, fifty-two square kilometers, with an eroded volcanic core surrounded by makatea ramparts as much as two kilometers wide. This is a limestone karst landscape riddled with caves and sinkholes and deeply cut by small streams that nearly disappear into the ground before ponding against the ramparts near the coast and dropping their sediment load. At these edges are swampy basins ideal for irrigated kalo culture but that account for just 2 percent of the total land area, with no more than another 18 percent available for dryland agriculture. Pollen coring and stratigraphy indicate that the island possessed extensive forests and marine and terrestrial resources, including a rich bird fauna, prior to human colonization about twenty-five hundred years ago. These resources were heavily exploited and crashed, resulting in faunal extinctions and the replacement of the forest with a pyrophytic landscape of scrub ironwood and ferns. The human population, divided into six districts with each ruled by a hereditary chief, eventually reached 150 persons per acre—very high even in Polynesian terms. Over time, competition for land became so severe that the political economy devolved into a permanent state of intertribal raiding and war, with victors seizing irrigated bottomlands and defeated groups taking refuge in cave systems on the upland makatea. There is plentiful evidence of human sacrifice and potentially outright cannibalism. In Kirch’s words, “Late precontact Mangaian society became . . . a society based on terror.”73 Similar trajectories are visible in the Marquesas; parts of New Zealand; Mangareva, which has some of the worst land degradation in Polynesia; and, most famously, Rapa Nui (Easter), where total deforestation led to spectacular social collapse, descent into warfare, cannibalism, and population crash.
In each case of environmental degradation, there was a parallel political evolution from a social hierarchy based on rigid hereditary chiefships to a more fluid one based on earned status, typically in the military sphere. In Mangaia and elsewhere, this transition proceeds in lockstep with the progress of environmental degradation. Kirch has described the process as “competitive involution” (borrowing and enlarging a concept from Clifford Geertz) where rapid population growth in areas of marginal, especially dry environments led to land degradation and fierce competition over resources “between inherently contradictory hereditary and achieved status positions.74 The result was an involuted cycle of prestige rivalry and competition that led as often to the destruction of the very means of production which were the objects of competition.”75
Easter Island is only the radical nightmare scenario of population “overshoot” of scarce resources leading to social collapse; to lesser degrees this process was ongoing in much of Polynesia by the eighteenth century. Fortunately, in only a handful of them had conditions worsened to such a grim point. These few, extreme examples naturally come from islands with marginal environments, whether due to makatea geology, remoteness, and/or small size—as with Henderson, Pitcairn, or the ten other small islands that Polynesians once inhabited but had abandoned by the time of European contact.76 This can help explain the rapidity of their transit through the phases Kirch catalogs—which we might better call socioenvironmental involution. Other places in Polynesia, with fewer obvious environmental limitations, appeared to be pushing against the door of involution in late prehistory: Tonga, the Societies, and other islands in the Cooks among them. While not every case of environmental vulnerability produced competitive involution, much less crash, the record promises some ability to predict these trajectories based on geography; after all, as Braudel formulized, “living standards are always a question of the number of people and the total resources at their disposal.”77 A bigger question is: What can the record of how they choose to dispose of their resources teach us?
EXPANSION INTO THE DRYLANDS
A new agricultural form appeared in Hawai‘i around AD 1400: intensive cultivation of ‘uala and other crops in unirrigated field systems constructed on broad slopes, mostly in leeward areas. Like the other Hawaiian farming types, this intensive rain-fed, or dryland, cultivation was unevenly distributed across the islands, being possible only where the right conditions existed: rocks old enough to form soils but not so old as to be leached and nutrient-poor, combined with enough rainfall to grow crops of mainly ‘uala, supplemented with dryland taro and kō but not so much as to leach away necessary nutrients. This “sweet spot” for sweet potatoes can be found only on the eastern islands—Kaua‘i and O‘ahu are too old geologically—and principally on the broad, unincised leeward slopes of Hawai‘i and East Maui running in horizontal bands between the dry coastline makai (below) and the wet forest mauka (above).78 On Maui, the Kahikinui and Kaupo field systems wrapped around the southeastern, leeward slopes of Haleakala; on Hawai‘i, traces of extensive field systems have been found in Kohala, Waimea, Kona, and Ka‘u. The best-preserved and most extensively studied, the Lower Kohala field system, covered sixty square kilometers over parts of thirty ahupua‘a and large ‘ili ‘āina with a dense, reticulate grid of stone walls delineating terraced gardens, water catchments, planting mounds, and trails, which also formed field boundaries. Interspersed among the productive infrastructure were house platforms, burial platforms, temples, and middens.79
The dryland fields were by nature less reliable food producers than irrigated pondfields, depending as they did on the vagaries of rainfall in a marginal environment where drought is a regular occurence. Kirch has suggested that farming families coped with the risks of variable climate by employing “bet-hedging agronomic strategies,” planting crops at several locations up and down the slope and thus, the rainfall gradient, to maximize their chances of a return.80 They also required more labor for weeding and especially mulching, including for “lithic” mulch, stones used to slow wind- and water-driven erosion and evaporation of moisture.81 On Maui and Hawai‘i, the women joined the men in the fields—something unknown on the other islands.82 The native Hawaiian historian David Malo wrote: “On lands supplied with running water, agriculture was easy and could be carried on at all times . . . On the kula lands farming was a laborious occupation and called for great patience, being attended with many drawbacks.”83 Areas of dryland culture, with unreliable water and thin, volcanic, chemically impoverished soils in place of the rich valley soils, were inherently marginal and more vulnerable to drought, fire, erosion, and soil exhaustion. Beyond these physical difficulties were social ones: Samuel Kamakau noted that “the women worked outside as hard as the men, often cooking, tilling the ground, and performing the duties in the house as well. This is why the chiefs of Hawai‘i imposed taxes on men and women alike and got the name of being oppressive to the people, while the chiefs of O‘ahu and Kaua‘i demanded taxes of the men alone.”84 Nevertheless, the enormous size of the larger field systems supported large populations: the Lower Kohala system may have been capable of supporting 15,480 to 30,960 persons, while the Kona field system’s population has been estimated at between 47,300 and 94,600.85 From its initial appearance, dryland cultivation on the eastern islands exploded, feeding populations that may have doubled in a single lifetime.86 By the end of
