Pacific islands in the Anthropocene

Although the islands of remote Oceania were among the last places reached by humanity, many islands entered the Anthropocene early. Extinctions — some caused by the first people to discover islands — have been far more frequent on islands than continents, and the intensity and consequences of human-caused biological invasion, deforestation, and landscape alteration have been substantially greater as well (Vitousek et al., 1997; Steadman, Pregill and Butley, 2002; Rolett and Diamond, 2004). At the same time, islands provide a useful model for understanding how coupled human and natural systems experience the Anthropocene, and perhaps for how they can manage its impacts. The Pacific islands of Polynesia are particularly interesting in this regard. As (Kirch, 2000, 2007a) pointed out, Polynesia consists of hundreds of islands — ranging from tropical atolls like the Tuamotus and Tuvalu; to volcanic high islands like Hawaii, Samoa, and Tahiti; to the subcontinental mass of New Zealand. All were discovered and colonized by people of the well-defined and highly dynamic Polynesian culture — who then developed a wide range of productive systems and social organizations based upon their cultural inheritance, the plants and animals they brought with them, and their interactions with their diverse islands. The cultural “adaptive radiation” they displayed is an unmatched model system for human-land interaction, in that one founding culture developed very different social organizations as well as resource acquisition practices in the very different islands they inhabited (Kirch, 1997). Moreover, Polynesian societies largely developed within the resources of their islands. Also, Polynesians had no access to stored energy from the past (fossil fuels), and their institutions, culture and values did not recognize borrowing from the future (discounting). Utilizing only the resources of their time and place, many islands developed remarkably populous, socially and culturally complex societies; for example, Hawaii probably supported a larger population on each of its larger islands (other than Oahu, where the city of Honolulu is located) at the time of European contact than it does now. We focus here on Polynesian agricultural systems, because agriculture generally represents the most important nexus between ecosystems and societies. Properties of the land shape how humans can farm, even as farming activities transform land. The Hawaiian Islands are particularly useful for understanding agricultural development — and human-land interactions more generally — for several reasons. First, the environmental matrix of the Hawaiian Archipelago can be used as a model for understanding soils and ecosystems independent of human action, as well as for understanding human societies; many of the fundamental controls of soils and ecosystems (e.g., parent material, topography, and biota) can be kept nearly constant across much of the Archipelago, while other fundamental controls (notably climate and substrate age) vary widely but in well-understood ways. These properties (and others) have been used to evaluate how nutrient supply and cycling are regulated as a function of rainfall (Chadwick et al., 2003), substrate age (Vitousek, 2004), and their interactions (Vitousek and Chadwick, 2013). Second, the agricultural systems of Hawaii (prior to European contact) were remarkable even within Polynesia for their scope, intensity, and originality. Third, while there is good evidence for two-way voyaging between Hawaii and elsewhere in Polynesia shortly after the islands were discovered, that voyaging appears to have ended several hundred years before European contact. As a result, both social and environmental dynamics internal to Hawaii were paramount; human-land interactions played out in isolation to a much greater extent than occurs in any continental situation. Finally, Hawaiian culture itself is vibrant and makes unique contributions to understanding the interaction of land and society. Prior to European contact in the late 18th Century, Hawaiians developed a wide diversity of agricultural practices that with some arbitrariness can be classified into intensive versus resource-concentrating cropping systems. Resource-concentrating systems include shifting cultivation, in which nutrients are accumulated over time in vegetation during a fallow phase; they also include systems that concentrate resources in space by gathering soil and/or mulch across a wide area and bringing it into (typically) pits or depressions where Domain Editor-in-Chief Donald R. Zak, University of Michigan