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Avoiding collapse: Pre-European sustainability on Pacific Islands
ARTICLE IN PRESS
Quaternary International 184 (2008) 4–10
Avoiding collapse: Pre-European sustainability on Pacific Islands Barry V. Rolett Department of Anthropology, University of Hawaii, HI 96822, USA Available online 26 October 2007
Abstract Both geography and cultural practices were important in guiding the ecological histories of Pacific Islands. This paper focuses on cases where cultural adaptation was the key to sustainability on small islands prone to deforestation. Environmental conditions including small island size and low rainfall required Polynesians to adapt their cultures and in some cases abandon the traditional reliance on shifting cultivation seen in the western Pacific. Successful adaptations involved avoiding agricultural strategies associated with fire while shifting to a reliance on irrigated pondfields or arboriculture. Easter Island, which suffered severe deforestation, is different from most other Pacific Islands because its environment is particularly fragile and there was no option for either irrigated agriculture or arboriculture. r 2007 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction All of eastern Polynesia was settled within a few centuries by a single people sharing the same ancestral culture. Following their initial discovery, some islands (like Easter Island) suffered human-induced environmental catastrophes and others were eventually abandoned after centuries of occupation. The potential for failure is clear; yet on a notable number of islands (including Tahiti and the Marquesas) Polynesians not only survived, but also flourished. The enduring inspiration of these microcosmic sustainable environments is recorded in the journals of eighteenth and nineteenth century European explorers, as well as in the literary and artistic works of Herman Melville, Robert Louis Stevenson, and Paul Gauguin. How do we explain the contrasting ecological histories of the Pacific Islands (Fig. 1)? What allowed for sustainable growth on some islands while on other islands environmental conditions steadily deteriorated following initial settlement? Geography plays a role. In a recent comparative study, Jared Diamond and I found that environmental factors including low rainfall and small land area make islands predisposed to deforestation while other conditions including high, mountainous terrain and proximity to sources of volcanic ash help maintain forest cover (Rolett and Diamond, 2004). While geography is important, E-mail address: [email protected]
cultural practices also guided the contrasting ecological histories of different islands. This paper looks at cases where cultural adaptation was the key to sustainability on small Polynesian islands. 2. The Pacific paradox The origins of Polynesians and most of their cultivated plants lie in the western Pacific (Kirch, 1984; Whistler, 1991). Polynesians depended upon introduced species because the native flora of islands in the eastern Pacific are almost completely lacking in edible plants. Major introduced cultigens include taro (Colocasia esculenta), bananas (Musa spp.), yams (Dioscorea spp.) and a range of tree crops such as breadfruit (Artocarpus altilis), the Tahitian chestnut (Inocarpus fagifer), and the Otahiete apple (Spondias dulcis). Throughout Southeast Asia and the western Pacific, where most of these plants were domesticated and first became established, the dominant agricultural strategy is dryland gardening, especially shifting cultivation (Conklin, 1957; Yen, 1990). In shifting cultivation, forested land is cleared with the use of fire, gardens are planted for a consecutive series of cropping cycles, and finally the fields are allowed to lie fallow. On the West Polynesian island of Futuna, for example, fields are typically cultivated for 3 years and allowed to lie fallow for 10 years before they are cleared and planted again (Kirch, 1994, p. 156). Shifting cultivation is
1040-6182/$ - see front matter r 2007 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2007.10.016
ARTICLE IN PRESS B.V. Rolett / Quaternary International 184 (2008) 4–10
5
, Hawai i
New Guinea Bismarcks Solomons
Marquesas
Vanuatu Futuna Fiji
Societies Cooks
Tuamotus
Tahiti
Australs Easter Island
Fig. 1. The Pacific Islands, showing locations discussed in the text.
considered extensive because increases in food production require increases in the size of the field system. For an active field system only about 25% of the land is cropped at any one time, while the rest of the land lies fallow (Kirch, 1994, p. 156). It is important to respect the fallow period or soil fertility declines over time, with a noticeable impact on crop yields. Shortages of arable land may cause farmers to reduce the fallow period or lengthen the cropping period. However, this is not a sustainable solution. Another option is mulching and fertilization to enhance the fertility of the soil. This practice is effective but labor intensive. The requirements for shifting cultivation pose a dilemma and a paradox for Pacific Islanders. The dilemma stems from the fact that a growing population requires a rapidly expanding field system. About 4 ha of land must be added to the field system to provide one new hectare of land for active cropping. Islanders who depend upon shifting cultivation must either contain population growth or continuously expand field systems. Expanding the field systems involves clearing forested land to plant gardens, so that food production requires the elimination of forests. This has both direct and indirect negative consequences. The main direct consequence of cutting forests is a shortage of timber resources, while the indirect consequences include erosion and runoff, both of which have negative impacts on soil fertility and the hydrological cycle. Thus, the paradox of shifting cultivation on small islands is that short-term benefits gained by expanding field systems are eventually outweighed by the negative effects of environmental degradation. 3. Sustainability: the wet and the dry Ethnobotanist Jacques Barrau’s classic study of agriculture in the Pacific (Barrau, 1965) highlights the dichotomy of the wet and the dry. The contrast, in essence, is between
crops (notably taro) that grow best in wet environments and others (such as yams) that favor drier conditions. The wet–dry contrast can also be extended, as shown by Kirch (1994, pp. 11–15), to basic geographic and climatic patterns in the Pacific. These include the windward–leeward contrasts in rainfall found on high islands that create orographic rain, as well as the general west to east trend of declining rainfall in the Pacific. The wet–dry contrast is also relevant to the study of sustainability. The western Pacific is a high rainfall zone, with annual rainfall of 3000 mm or more even in leeward settings. Most western Pacific Islands, including the Bismarck and Solomon archipelagoes, are large and mountainous. New Britain (Bismarcks), for example, has a land area of 35,742 km2 and the major islands in the Solomons range from 3000 to 8500 km2 in size. These were the first archipelagoes settled as people began to colonize the Pacific. Shifting cultivation of rainfed gardens has remained the dominant strategy since the beginning of agriculture in this region, with arboriculture as a secondary component of food production systems. Despite 30,000 years or more of human settlement and a reliance on shifting cultivation for at least 4000 years, the Bismarcks and the Solomons remained densely forested until the advent of modern clear-cutting. Environmental factors that aided the retention of forest cover include high rainfall, large island size, and high levels of volcanic ash (Rolett and Diamond, 2004). Population control was another important factor contributing to the retention of these forests. Human population levels are less dense in the western Pacific than in the east, even though islands in the west have been occupied for a far longer period of time. The discrepancy in population densities can be explained by diseases including malaria which are endemic in the west but absent east of Vanuatu. Disease apparently played a long-term role in suppressing population levels in the west (Groube, 1993, p. 177; Kirch, 2000, pp. 83–84).
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In summary, the general environmental setting for the western Pacific is one of large islands with high rainfall and fertile soils enriched by ash fallout from volcanic eruptions. These environmental factors, together with low population densities likely linked to the endemic presence of malaria, favor the growth and retention of forests even despite the widespread reliance on shifting cultivation. The situation in the eastern Pacific is far different. East Polynesian islands including Tahiti, the Cooks, the Australs, the Tuamotus, the Marquesas, Hawaii, and Easter Island offer a striking contrast to the west Pacific archipelagoes. First, they are comparatively small; only a few islands in Hawaii have a land area greater than 1000 km2, while most of the East Polynesian islands are smaller than 200 km2 in size. In the Cooks and the Australs, for example, the largest island is 70 km2 and there are other permanently inhabited islands that are as small as 9 km2. It is also significant that rainfall in the eastern Pacific is low in comparison with the western Pacific. In most leeward settings rainfall on islands in the east is o2500 mm/year and in many cases it is o1000 mm/year. Small island size and low rainfall stand out among the conditions that required Polynesians to adapt their cultures in order to survive and thrive in the eastern Pacific. This is partly because small, dry islands are more prone to deforestation than large islands (Rolett and Diamond, 2004). Polynesians on small, dry islands were forced to reconsider, and in some cases abandon, the traditional reliance on shifting cultivation seen in the western Pacific. 3.1. The advantages of irrigation Cultural adaptation in Polynesia is central for understanding the emergence of sustainability on environmentally diverse islands. One prominent development was the adoption of irrigated agriculture. In the Pacific, irrigated agriculture is synonymous with taro. Taro thrives in humid settings such as freshwater swamps but it grows best in pondfield systems where water is diverted from a stream to artificially terraced fields and allowed to flow from one flooded field to the next (Fig. 2). Although taro can also be grown in rainfed gardens, there are many advantages of growing it in an irrigated setting, as Spriggs (1990) describes in a paper aptly entitled ‘‘Why irrigation matters in the Pacific.’’ These advantages include: (1) crop yields are significantly higher in irrigated fields (up to 35 mt/ha/year vs. 2.5–15 mt/ha/year in rainfed gardens); (2) irrigation transforms potentially marginal agricultural land such as swamps into highly productive fields; and (3) irrigation allows nearly constant cropping, with minimal fallow time (Spriggs, 1990). Using the example of Futuna again, irrigated fields are cropped for about 4 years, followed by a 1 year fallow period before the beginning of a new cropping cycle Kirch (1994, p. 156). By contrast, Futuna’s rainfed gardens are cropped for only 3 years followed by a 10 year fallow period, highlighting the extensive character of shifting cultivation in comparison with irrigated agriculture (Kirch, 1994, p. 156).
Fig. 2. Taro growing in irrigated terraces on Rarotonga, Cook Islands (photo by B. Rolett, February 1981).
In addition to these advantages listed by Spriggs, we can add two more. First, the flooding of pondfields helps to maintain an open habitat suitable for cultivation. Second, irrigated agriculture does not require the use of fire. This is an advantage on dry islands where fires can burn out of control. Savannah grasslands of Miscanthus floridulus, sometimes merging into Dicranopteris fernlands, become established in cleared areas maintained by habitual burning (Fig. 3). These grasslands are an anthropogenic vegetation zone, as observed by the American explorer Charles Wilkes in Fiji: ybelow the elevation of one thousand feet, on the leeward side of the large islands, the original vegetation has been for the most part destroyed by the fires which the natives use to clear their planting grounds. During our sojourn we occasionally saw the fire running over vast fields. The forest above that elevation, having escaped its ravages, forms umbrageous massesy (Wilkes, 1845, p. 340) Fire-associated grasslands unsuitable for cultivation cover large tracts of dry islands throughout the eastern Pacific and they serve as a quantitative measure of anthropogenic deforestation (Decker, 1970, pp. 236–241).
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Fig. 3. A fire burning out of control in Vaitahu Valley, Tahuata, Marquesas Islands. The fire spread from shifting cultivation garden plots to savannah grasslands of Miscanthus floridulus growing on the ridges (photo by B. Rolett, July 2006).
European-contact era descriptions of vegetation are available for most of the inhabited high islands in the Polynesian archipelagoes of Hawaii, the Societies, the Cooks, the Australs, and the Marquesas. They reveal that all of these islands were partly deforested, with fireassociated grasslands widespread along ridges, slopes, and plateaus (Rolett and Diamond, 2004). The Marquesas are a good example. M. floridulus grasslands cover the lower ridges and forest cover is mainly on the coastal plains, in valleys, and on the highest, wettest slopes (Fig. 4). The M. floridulus grasslands of Vaitahu, a leeward Marquesan valley, are visible in Fig. 4 as light-colored areas on ridges leading up to the central mountain range. They are a permanent type of vegetation already well established by the early European contact period (Rolett, 1998, p. 29). On islands vulnerable to deforestation, irrigated agriculture allows for the intensive cultivation of less land than would be needed if the same crop yields were to be produced through shifting cultivation. Thus, irrigated agriculture contributes to sustainability by limiting the amount of arable land needed for food production and by decreasing the use of fire on islands predisposed to deforestation. Tellingly, irrigated agriculture was important throughout most of Polynesia, on nearly all islands predisposed to deforestation. In Spriggs’ words: ‘‘when people could irrigate they usually did, and intensive dryland systems were adopted very much as a second choice’’ (1990, p. 185). 3.2. Easter Island Despite its advantages, there are islands in Polynesia where irrigated agriculture was not feasible, and the outcomes on these islands offer further insight for the study of sustainability. Easter Island, known to its inhab-
Fig. 4. View of Vaitahu Valley, Tahuata, Marquesas Islands. Miscanthus grasslands are visible as light-colored areas on ridges leading up to the central mountain range (photo by B. Rolett, July 1998).
itants as Rapa Nui, is a prominent example. Easter has no permanently flowing streams and although Polynesians successfully introduced taro, there is no evidence for irrigated agriculture (Forster, 1982, p. 471; Stevenson et al., 2006). Taro, like sweet potatoes and yams, was cultivated in rainfed gardens using mulching, fertilization, and water retention techniques (La Pe´rouse, 1799, p. 19; Forster, 1982, p. 471; Forster, 2000, p. 307; Stevenson et al., 2006). This system of rainfed cultivation was adapted to become increasingly intensive over time (Stevenson et al., 2006), but Easter Island still suffered the worst preEuropean history of deforestation in the Pacific (Bahn and Flenley, 2003). The island was nearly completely deforested by the time of European contact, prompting one of the first European visitors to write: ‘‘Trees are very scarce, we did not even see a single one worthy of the name’’ (La Pe´rouse, 1799, p. 197). What precipitated Easter Island’s environmental collapse? There is debate over which factors played a leading role. One view stresses the importance of rats introduced by Polynesian settlers. This hypothesis suggests that rat populations multiplied exponentially in the first years following their arrival, feeding on ground-nesting
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seabirds and nuts of the giant, now extinct palm which dominated Easter’s forests. It is argued that rats had an impact even more devastating than that of the first humans, and that they deforested the island by inhibiting regeneration of the palm forests (Hunt, 2006, 2007). Hunt (2006, p. 419) suggests that ‘‘it was rats, more so than humans, that led to deforestation.’’ While this argument is attractive because it absolves Polynesians from having intentionally deforested the island, it is contradicted by multiple lines of evidence discussed by Diamond (2007) as well as Flenley and Bahn (2007). First, although rats may have slowed regrowth of Easter’s palm forests, they could not have felled the mature trees. These had a life span of up to 2000 years, yet the palms mostly vanished within a few centuries following the arrival of humans and rats (Flenley and Bahn, 2007). This draws attention to the role of humans. The first settlers cleared large areas of the palm forests (by cutting and with the use of fire) and planted extensive open-field gardens beginning shortly after initial colonization (Mieth and Bork, 2003; Stevenson et al., 2006). Evidence for cutting and burning the palms is found in the form of numerous palm stumps, many of which are burnt. Fire would have posed a severe threat to Easter’s palms, greater than the threat of rats. This is because palm forests are highly inflammable, since fronds among the ground litter are easily ignited and fire spreads rapidly once it reaches the tree canopy. Such a disaster occurred on the uninhabited Hawaiian island of Nihoa which was densely forested by native palms until 1885 when visitors from Honolulu accidentally ignited a blaze that swept over the entire island, burning almost all of the palms (Evenhuis and Eldredge, 2004). The risk of fire is greatest on dry islands and Easter is one of the driest inhabited islands in the Pacific. In addition to low rainfall, Easter Island also stands out in terms of other environmental factors that increase the likelihood of deforestation. Comparative analysis of the Pacific islands shows that small, dry, cool, remote islands, with low topography, low inputs of soil-enriching continental dust, and little or no volcanic ash fallout are the most vulnerable to deforestation (Rolett and Diamond, 2004). Easter ranks near the top in terms of all these factors that predispose toward deforestation, supporting the view that: ‘‘Easter’s collapse was not because its people were especially improvident but because they faced one of the Pacific’s most fragile environments’’ (Rolett and Diamond, 2004, p. 445). In this sense, the Polynesians who settled Easter Island were ‘‘cursed by poor location’’ (Gee, 2004, p. 411). It was particularly difficult to adapt to this fragile environment because there was no possibility of developing irrigated agriculture, which was such a successful solution for many small islands in the east Pacific. Another factor is the absence of the two most important Polynesian tree crops, breadfruit and the Tahitian chestnut, neither of which reached Easter. This precluded the option of developing arboriculture, a strategy that proved crucial
for Polynesians on other islands who managed to avoid an environmental collapse. 3.3. The advantages of arboriculture The Marquesas, 1200 km east of Tahiti, are also characterized by many of the same environmental traits that made Easter’s forests fragile. Most of the leeward settings receive less than Easter’s average annual rainfall of 1198 mm/year. Although some windward areas are somewhat wetter (up to 2400 mm/year or more) because of orographic rain generated by mountains, the Marquesas have one of the most unpredictable rainfall patterns in the Pacific. They are subject to prolonged droughts (lasting up to 3 years) that can cause catastrophic famines resulting from crop failure (Rolett, 1998, p. 25). Taro is present but irrigated pondfields are highly localized and for the most part absent in the Marquesas. This is due to the scarcity of streams with constant flows of water. The Marquesas would seem to represent an extreme case of the Pacific paradox, in which efforts to expand shifting cultivation field systems lead to deforestation and environmental degradation on small, dry islands. However, despite the risk of environmental collapse, Marquesans succeeded in maintaining both their forests and a thriving human population. How did they adapt to an environment that is too dry for irrigated agriculture, and where, as on Easter, shifting cultivation is unsustainable? The solution was development of a food production system focused on arboriculture. By relying on arboriculture rather than shifting cultivation, Marquesans minimized the use of fire in their fields, as well as the danger of accidental fires, the damaging effects of which could not be tolerated over the long-term. Marquesans introduced most of the cultivated plants comprising the typical Pacific Islands ‘‘transported landscape’’ (Kirch, 1984). They further transformed the vegetational environment by forest replacement, the replacement of native trees with useful introduced tree species (Rolett and Diamond, 2004). Marquesan arboriculture centers around breadfruit, a tree crop that was likely domesticated in New Guinea and which Pacific Islanders introduced to most of the islands they settled (Yen, 1990) (Fig. 5). Arboriculture, also including cultivation of the Tahitian chestnut and various sweet fruits, is a component of most Pacific Island economies but it reached its apogee in East Polynesia, especially the Marquesas. Breadfruit is a seasonal crop but it can be stored in pits where, through a process of anaerobic fermentation, the starchy fruit turns to a sour paste that remains edible for years, even decades, as long as the pit is sealed (Rolett, 1998, p. 34). Although breadfruit is dominated by seeded varieties in the western Pacific, Polynesians selected for seedless varieties because these are best suited for making the fermented paste. Marquesans recognize at least 33 varieties of breadfruit, almost all of which are seedless (Christian, 1910, p. 208). The central
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discussed here is comforting because it shows that fundamental environmental crises faced by the global community today (the shortage of natural resources and human-induced environmental degradation) are ones which Polynesians, living in extreme isolation, also faced and survived. Our formula for success must surely involve avoiding the obvious causes of failure, together with innovation, and long-term resolve. Acknowledgments I am grateful to Yoshinori Yasuda for stimulating my interest in sustainable environments and for inviting me to the symposium at Lake Towada in Japan where an early version of this paper was presented. I thank Peter Matthews for valuable comments on the manuscript. References
Fig. 5. Breadfruit tree growing in the Marquesas Islands (photo by B. Rolett, December 1985).
role of breadfruit in the Marquesas is well described by an early American visitor, Captain David Porter. Porter wrote: The breadfruit tree is every thing to the natives of these islandsy Describe to one of the nativesy a country abounding in every thing that we consider desirable, and after you are done, he will ask you if it provides breadfruit. A country is nothing to them without that blessing, and the season for breadfruit is the time for joy and festivity. (Porter, 1822, pp. 54–55) With forests providing their main source of food, Marquesans avoided the need to rely on shifting cultivation. This adaptation created two benefits. Marquesans were not forced to sacrifice their forests in order to develop and expand their subsistence economy. They also reduced the risk of accidental fires by minimizing the practice of burning fields. 4. Epilogue The formula for sustainability on small, dry islands involves avoiding agricultural strategies associated with fire, while shifting to a reliance on irrigated pondfields or arboriculture. Success was essentially a result of avoiding the continuous expansion of shifting cultivation field systems and the use of fire. The history of Easter Island differs in comparison with that of most other Pacific Islands because its environment is particularly fragile and there was no option for either irrigated agriculture or arboriculture. Knowledge gained from the case studies
Bahn, P., Flenley, J.R., 2003. The Enigmas of Easter Island. Oxford University Press, Oxford. Barrau, J., 1965. L’humide et le sec: an essay on ethnobiological adaptation to contrastive environments in the Indo-Pacific area. Journal of the Polynesian Society 74, 329–346. Christian, F.W., 1910. Eastern Pacific Lands: Tahiti and the Marquesas Islands. Robert Scott, London. Conklin, H.C., 1957. Hanunoo agriculture: a report on an integral system of shifting cultivation in the Philippines. Forestry Development Paper No. 12, Food and Agriculture Organization of the United Nations, Rome. Decker, B.G., 1970. Plants, man and landscape in Marquesan valleys, French Polynesia. Ph.D. Dissertation, University of California, Berkeley. Diamond, J., 2007. Easter Island revisited. Science 317, 1692–1694. Evenhuis, N.L., Eldredge, L.G., 2004. Natural History of Nihoa and Necker Islands. Bishop Museum Press, Honolulu. Flenley, J., Bahn, P., 2007. Conflicting views of Easter Island. Rapa Nui Journal 21 (1), 11–13. Forster, J.R., 1982. In: Hoare, M.E. (Ed.), The Resolution Journal of Johann Reinhold Forster, vols. 1772–1775. Hakluyt Society, Cambridge. Forster, G., 2000. A Voyage Round the World. University of Hawaii Press, Honolulu. Gee, H., 2004. Treeless at Easter. Nature 431, 411. Groube, L.M., 1993. Contradictions and malaria in Melanesian and Australian prehistory. In: Smith, M.A., Spriggs, M., Fankhauser, B. (Eds.), Sahul in Review: Pleistocene Archaeology in Australia, New Guinea, and Island Melanesia. Occasional Papers in Prehistory No. 24, Department of Prehistory, Australian National University, Canberra, pp. 164–186. Hunt, T.L., 2006. Rethinking the fall of Easter Island. American Scientist 94, 412–419. Hunt, T.L., 2007. Rethinking Easter Island’s ecological catastrophe. Journal of Archaeological Science 34, 485–502. Kirch, P.V., 1984. The Evolution of the Polynesian Chiefdoms. Cambridge University Press, Cambridge. Kirch, P.V., 1994. The Wet and the Dry: Irrigation and Agricultural Intensification in Polynesia. University of Chicago Press, Chicago. Kirch, P.V., 2000. On the Road of the Winds: An Archaeological History of the Pacific Islands before European Contact. University of California Press, Berkeley. La Pe´rouse, J.F.G., 1799. A Voyage Round the World in the Years 1785, 1786, 1787, and 1788y, vol. II. J. Johnson, London.
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Mieth, A., Bork, H., 2003. Dimunition and degradation of environmental resources by prehistoric land use on Poike Penisula, Easter Island (Rapa Nui). Rapa Nui Journal 17 (1), 34–41. Porter, D., 1822. Journal of a Cruise Made to the Pacific Ocean in the United States Frigate Essex, 1812, 1813, 1814, second ed. Wiley, New York, (2 vols.). Rolett, B.V., 1998. Hanamiai: prehistoric colonization and cultural change in the Marquesas Islands (East Polynesia). Yale University Publications in Anthropology Number 81. Department of Anthropology, New Haven, and The Peabody Museum, Yale University. Rolett, B.V., Diamond, J., 2004. Environmental predictors of pre-European deforestation on Pacific Islands. Nature 431, 443–446. Spriggs, M.J.T., 1990. Why irrigation matters in the Pacific. In: Yen, D.E. (Ed.), Pacific Production Systems: Approaches to Economic Prehis-
tory. Department of Prehistory, Australian National University, Canberra, pp. 174–189. Stevenson, C.M., Jackson, T.L., Mieth, M., Bork, H., Ladefoged, T.N., 2006. Prehistoric and early historic agriculture at Maunga Orito, Easter Island (Rapa Nui), Chile. Antiquity 80, 919–936. Whistler, W.A., 1991. Polynesian plant introductions. In: Cox, P.A., Banack, S.A. (Eds.), Islands, Plants, and Polynesians: An Introduction to Polynesian Ethnobotany. Dioscorides Press, Portland, Oregon, pp. 41–66. Wilkes, C., 1845. Narrative of the United States Exploring Expedition during the Years 1838, 1839, 1840, 1841, 1842, vol. II. Lea & Blanchard, Philadelphia. Yen, D.E., 1990. Environment, agriculture, and the colonisation of the Pacific. In: Yen, D.E. (Ed.), Pacific Production Systems: Approaches to Economic Prehistory. Department of Prehistory, Australian National University, Canberra, pp. 258–277.
Quaternary International 184 (2008) 4–10
Avoiding collapse: Pre-European sustainability on Pacific Islands Barry V. Rolett Department of Anthropology, University of Hawaii, HI 96822, USA Available online 26 October 2007
Abstract Both geography and cultural practices were important in guiding the ecological histories of Pacific Islands. This paper focuses on cases where cultural adaptation was the key to sustainability on small islands prone to deforestation. Environmental conditions including small island size and low rainfall required Polynesians to adapt their cultures and in some cases abandon the traditional reliance on shifting cultivation seen in the western Pacific. Successful adaptations involved avoiding agricultural strategies associated with fire while shifting to a reliance on irrigated pondfields or arboriculture. Easter Island, which suffered severe deforestation, is different from most other Pacific Islands because its environment is particularly fragile and there was no option for either irrigated agriculture or arboriculture. r 2007 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction All of eastern Polynesia was settled within a few centuries by a single people sharing the same ancestral culture. Following their initial discovery, some islands (like Easter Island) suffered human-induced environmental catastrophes and others were eventually abandoned after centuries of occupation. The potential for failure is clear; yet on a notable number of islands (including Tahiti and the Marquesas) Polynesians not only survived, but also flourished. The enduring inspiration of these microcosmic sustainable environments is recorded in the journals of eighteenth and nineteenth century European explorers, as well as in the literary and artistic works of Herman Melville, Robert Louis Stevenson, and Paul Gauguin. How do we explain the contrasting ecological histories of the Pacific Islands (Fig. 1)? What allowed for sustainable growth on some islands while on other islands environmental conditions steadily deteriorated following initial settlement? Geography plays a role. In a recent comparative study, Jared Diamond and I found that environmental factors including low rainfall and small land area make islands predisposed to deforestation while other conditions including high, mountainous terrain and proximity to sources of volcanic ash help maintain forest cover (Rolett and Diamond, 2004). While geography is important, E-mail address: [email protected]
cultural practices also guided the contrasting ecological histories of different islands. This paper looks at cases where cultural adaptation was the key to sustainability on small Polynesian islands. 2. The Pacific paradox The origins of Polynesians and most of their cultivated plants lie in the western Pacific (Kirch, 1984; Whistler, 1991). Polynesians depended upon introduced species because the native flora of islands in the eastern Pacific are almost completely lacking in edible plants. Major introduced cultigens include taro (Colocasia esculenta), bananas (Musa spp.), yams (Dioscorea spp.) and a range of tree crops such as breadfruit (Artocarpus altilis), the Tahitian chestnut (Inocarpus fagifer), and the Otahiete apple (Spondias dulcis). Throughout Southeast Asia and the western Pacific, where most of these plants were domesticated and first became established, the dominant agricultural strategy is dryland gardening, especially shifting cultivation (Conklin, 1957; Yen, 1990). In shifting cultivation, forested land is cleared with the use of fire, gardens are planted for a consecutive series of cropping cycles, and finally the fields are allowed to lie fallow. On the West Polynesian island of Futuna, for example, fields are typically cultivated for 3 years and allowed to lie fallow for 10 years before they are cleared and planted again (Kirch, 1994, p. 156). Shifting cultivation is
1040-6182/$ - see front matter r 2007 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2007.10.016
ARTICLE IN PRESS B.V. Rolett / Quaternary International 184 (2008) 4–10
5
, Hawai i
New Guinea Bismarcks Solomons
Marquesas
Vanuatu Futuna Fiji
Societies Cooks
Tuamotus
Tahiti
Australs Easter Island
Fig. 1. The Pacific Islands, showing locations discussed in the text.
considered extensive because increases in food production require increases in the size of the field system. For an active field system only about 25% of the land is cropped at any one time, while the rest of the land lies fallow (Kirch, 1994, p. 156). It is important to respect the fallow period or soil fertility declines over time, with a noticeable impact on crop yields. Shortages of arable land may cause farmers to reduce the fallow period or lengthen the cropping period. However, this is not a sustainable solution. Another option is mulching and fertilization to enhance the fertility of the soil. This practice is effective but labor intensive. The requirements for shifting cultivation pose a dilemma and a paradox for Pacific Islanders. The dilemma stems from the fact that a growing population requires a rapidly expanding field system. About 4 ha of land must be added to the field system to provide one new hectare of land for active cropping. Islanders who depend upon shifting cultivation must either contain population growth or continuously expand field systems. Expanding the field systems involves clearing forested land to plant gardens, so that food production requires the elimination of forests. This has both direct and indirect negative consequences. The main direct consequence of cutting forests is a shortage of timber resources, while the indirect consequences include erosion and runoff, both of which have negative impacts on soil fertility and the hydrological cycle. Thus, the paradox of shifting cultivation on small islands is that short-term benefits gained by expanding field systems are eventually outweighed by the negative effects of environmental degradation. 3. Sustainability: the wet and the dry Ethnobotanist Jacques Barrau’s classic study of agriculture in the Pacific (Barrau, 1965) highlights the dichotomy of the wet and the dry. The contrast, in essence, is between
crops (notably taro) that grow best in wet environments and others (such as yams) that favor drier conditions. The wet–dry contrast can also be extended, as shown by Kirch (1994, pp. 11–15), to basic geographic and climatic patterns in the Pacific. These include the windward–leeward contrasts in rainfall found on high islands that create orographic rain, as well as the general west to east trend of declining rainfall in the Pacific. The wet–dry contrast is also relevant to the study of sustainability. The western Pacific is a high rainfall zone, with annual rainfall of 3000 mm or more even in leeward settings. Most western Pacific Islands, including the Bismarck and Solomon archipelagoes, are large and mountainous. New Britain (Bismarcks), for example, has a land area of 35,742 km2 and the major islands in the Solomons range from 3000 to 8500 km2 in size. These were the first archipelagoes settled as people began to colonize the Pacific. Shifting cultivation of rainfed gardens has remained the dominant strategy since the beginning of agriculture in this region, with arboriculture as a secondary component of food production systems. Despite 30,000 years or more of human settlement and a reliance on shifting cultivation for at least 4000 years, the Bismarcks and the Solomons remained densely forested until the advent of modern clear-cutting. Environmental factors that aided the retention of forest cover include high rainfall, large island size, and high levels of volcanic ash (Rolett and Diamond, 2004). Population control was another important factor contributing to the retention of these forests. Human population levels are less dense in the western Pacific than in the east, even though islands in the west have been occupied for a far longer period of time. The discrepancy in population densities can be explained by diseases including malaria which are endemic in the west but absent east of Vanuatu. Disease apparently played a long-term role in suppressing population levels in the west (Groube, 1993, p. 177; Kirch, 2000, pp. 83–84).
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In summary, the general environmental setting for the western Pacific is one of large islands with high rainfall and fertile soils enriched by ash fallout from volcanic eruptions. These environmental factors, together with low population densities likely linked to the endemic presence of malaria, favor the growth and retention of forests even despite the widespread reliance on shifting cultivation. The situation in the eastern Pacific is far different. East Polynesian islands including Tahiti, the Cooks, the Australs, the Tuamotus, the Marquesas, Hawaii, and Easter Island offer a striking contrast to the west Pacific archipelagoes. First, they are comparatively small; only a few islands in Hawaii have a land area greater than 1000 km2, while most of the East Polynesian islands are smaller than 200 km2 in size. In the Cooks and the Australs, for example, the largest island is 70 km2 and there are other permanently inhabited islands that are as small as 9 km2. It is also significant that rainfall in the eastern Pacific is low in comparison with the western Pacific. In most leeward settings rainfall on islands in the east is o2500 mm/year and in many cases it is o1000 mm/year. Small island size and low rainfall stand out among the conditions that required Polynesians to adapt their cultures in order to survive and thrive in the eastern Pacific. This is partly because small, dry islands are more prone to deforestation than large islands (Rolett and Diamond, 2004). Polynesians on small, dry islands were forced to reconsider, and in some cases abandon, the traditional reliance on shifting cultivation seen in the western Pacific. 3.1. The advantages of irrigation Cultural adaptation in Polynesia is central for understanding the emergence of sustainability on environmentally diverse islands. One prominent development was the adoption of irrigated agriculture. In the Pacific, irrigated agriculture is synonymous with taro. Taro thrives in humid settings such as freshwater swamps but it grows best in pondfield systems where water is diverted from a stream to artificially terraced fields and allowed to flow from one flooded field to the next (Fig. 2). Although taro can also be grown in rainfed gardens, there are many advantages of growing it in an irrigated setting, as Spriggs (1990) describes in a paper aptly entitled ‘‘Why irrigation matters in the Pacific.’’ These advantages include: (1) crop yields are significantly higher in irrigated fields (up to 35 mt/ha/year vs. 2.5–15 mt/ha/year in rainfed gardens); (2) irrigation transforms potentially marginal agricultural land such as swamps into highly productive fields; and (3) irrigation allows nearly constant cropping, with minimal fallow time (Spriggs, 1990). Using the example of Futuna again, irrigated fields are cropped for about 4 years, followed by a 1 year fallow period before the beginning of a new cropping cycle Kirch (1994, p. 156). By contrast, Futuna’s rainfed gardens are cropped for only 3 years followed by a 10 year fallow period, highlighting the extensive character of shifting cultivation in comparison with irrigated agriculture (Kirch, 1994, p. 156).
Fig. 2. Taro growing in irrigated terraces on Rarotonga, Cook Islands (photo by B. Rolett, February 1981).
In addition to these advantages listed by Spriggs, we can add two more. First, the flooding of pondfields helps to maintain an open habitat suitable for cultivation. Second, irrigated agriculture does not require the use of fire. This is an advantage on dry islands where fires can burn out of control. Savannah grasslands of Miscanthus floridulus, sometimes merging into Dicranopteris fernlands, become established in cleared areas maintained by habitual burning (Fig. 3). These grasslands are an anthropogenic vegetation zone, as observed by the American explorer Charles Wilkes in Fiji: ybelow the elevation of one thousand feet, on the leeward side of the large islands, the original vegetation has been for the most part destroyed by the fires which the natives use to clear their planting grounds. During our sojourn we occasionally saw the fire running over vast fields. The forest above that elevation, having escaped its ravages, forms umbrageous massesy (Wilkes, 1845, p. 340) Fire-associated grasslands unsuitable for cultivation cover large tracts of dry islands throughout the eastern Pacific and they serve as a quantitative measure of anthropogenic deforestation (Decker, 1970, pp. 236–241).
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Fig. 3. A fire burning out of control in Vaitahu Valley, Tahuata, Marquesas Islands. The fire spread from shifting cultivation garden plots to savannah grasslands of Miscanthus floridulus growing on the ridges (photo by B. Rolett, July 2006).
European-contact era descriptions of vegetation are available for most of the inhabited high islands in the Polynesian archipelagoes of Hawaii, the Societies, the Cooks, the Australs, and the Marquesas. They reveal that all of these islands were partly deforested, with fireassociated grasslands widespread along ridges, slopes, and plateaus (Rolett and Diamond, 2004). The Marquesas are a good example. M. floridulus grasslands cover the lower ridges and forest cover is mainly on the coastal plains, in valleys, and on the highest, wettest slopes (Fig. 4). The M. floridulus grasslands of Vaitahu, a leeward Marquesan valley, are visible in Fig. 4 as light-colored areas on ridges leading up to the central mountain range. They are a permanent type of vegetation already well established by the early European contact period (Rolett, 1998, p. 29). On islands vulnerable to deforestation, irrigated agriculture allows for the intensive cultivation of less land than would be needed if the same crop yields were to be produced through shifting cultivation. Thus, irrigated agriculture contributes to sustainability by limiting the amount of arable land needed for food production and by decreasing the use of fire on islands predisposed to deforestation. Tellingly, irrigated agriculture was important throughout most of Polynesia, on nearly all islands predisposed to deforestation. In Spriggs’ words: ‘‘when people could irrigate they usually did, and intensive dryland systems were adopted very much as a second choice’’ (1990, p. 185). 3.2. Easter Island Despite its advantages, there are islands in Polynesia where irrigated agriculture was not feasible, and the outcomes on these islands offer further insight for the study of sustainability. Easter Island, known to its inhab-
Fig. 4. View of Vaitahu Valley, Tahuata, Marquesas Islands. Miscanthus grasslands are visible as light-colored areas on ridges leading up to the central mountain range (photo by B. Rolett, July 1998).
itants as Rapa Nui, is a prominent example. Easter has no permanently flowing streams and although Polynesians successfully introduced taro, there is no evidence for irrigated agriculture (Forster, 1982, p. 471; Stevenson et al., 2006). Taro, like sweet potatoes and yams, was cultivated in rainfed gardens using mulching, fertilization, and water retention techniques (La Pe´rouse, 1799, p. 19; Forster, 1982, p. 471; Forster, 2000, p. 307; Stevenson et al., 2006). This system of rainfed cultivation was adapted to become increasingly intensive over time (Stevenson et al., 2006), but Easter Island still suffered the worst preEuropean history of deforestation in the Pacific (Bahn and Flenley, 2003). The island was nearly completely deforested by the time of European contact, prompting one of the first European visitors to write: ‘‘Trees are very scarce, we did not even see a single one worthy of the name’’ (La Pe´rouse, 1799, p. 197). What precipitated Easter Island’s environmental collapse? There is debate over which factors played a leading role. One view stresses the importance of rats introduced by Polynesian settlers. This hypothesis suggests that rat populations multiplied exponentially in the first years following their arrival, feeding on ground-nesting
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seabirds and nuts of the giant, now extinct palm which dominated Easter’s forests. It is argued that rats had an impact even more devastating than that of the first humans, and that they deforested the island by inhibiting regeneration of the palm forests (Hunt, 2006, 2007). Hunt (2006, p. 419) suggests that ‘‘it was rats, more so than humans, that led to deforestation.’’ While this argument is attractive because it absolves Polynesians from having intentionally deforested the island, it is contradicted by multiple lines of evidence discussed by Diamond (2007) as well as Flenley and Bahn (2007). First, although rats may have slowed regrowth of Easter’s palm forests, they could not have felled the mature trees. These had a life span of up to 2000 years, yet the palms mostly vanished within a few centuries following the arrival of humans and rats (Flenley and Bahn, 2007). This draws attention to the role of humans. The first settlers cleared large areas of the palm forests (by cutting and with the use of fire) and planted extensive open-field gardens beginning shortly after initial colonization (Mieth and Bork, 2003; Stevenson et al., 2006). Evidence for cutting and burning the palms is found in the form of numerous palm stumps, many of which are burnt. Fire would have posed a severe threat to Easter’s palms, greater than the threat of rats. This is because palm forests are highly inflammable, since fronds among the ground litter are easily ignited and fire spreads rapidly once it reaches the tree canopy. Such a disaster occurred on the uninhabited Hawaiian island of Nihoa which was densely forested by native palms until 1885 when visitors from Honolulu accidentally ignited a blaze that swept over the entire island, burning almost all of the palms (Evenhuis and Eldredge, 2004). The risk of fire is greatest on dry islands and Easter is one of the driest inhabited islands in the Pacific. In addition to low rainfall, Easter Island also stands out in terms of other environmental factors that increase the likelihood of deforestation. Comparative analysis of the Pacific islands shows that small, dry, cool, remote islands, with low topography, low inputs of soil-enriching continental dust, and little or no volcanic ash fallout are the most vulnerable to deforestation (Rolett and Diamond, 2004). Easter ranks near the top in terms of all these factors that predispose toward deforestation, supporting the view that: ‘‘Easter’s collapse was not because its people were especially improvident but because they faced one of the Pacific’s most fragile environments’’ (Rolett and Diamond, 2004, p. 445). In this sense, the Polynesians who settled Easter Island were ‘‘cursed by poor location’’ (Gee, 2004, p. 411). It was particularly difficult to adapt to this fragile environment because there was no possibility of developing irrigated agriculture, which was such a successful solution for many small islands in the east Pacific. Another factor is the absence of the two most important Polynesian tree crops, breadfruit and the Tahitian chestnut, neither of which reached Easter. This precluded the option of developing arboriculture, a strategy that proved crucial
for Polynesians on other islands who managed to avoid an environmental collapse. 3.3. The advantages of arboriculture The Marquesas, 1200 km east of Tahiti, are also characterized by many of the same environmental traits that made Easter’s forests fragile. Most of the leeward settings receive less than Easter’s average annual rainfall of 1198 mm/year. Although some windward areas are somewhat wetter (up to 2400 mm/year or more) because of orographic rain generated by mountains, the Marquesas have one of the most unpredictable rainfall patterns in the Pacific. They are subject to prolonged droughts (lasting up to 3 years) that can cause catastrophic famines resulting from crop failure (Rolett, 1998, p. 25). Taro is present but irrigated pondfields are highly localized and for the most part absent in the Marquesas. This is due to the scarcity of streams with constant flows of water. The Marquesas would seem to represent an extreme case of the Pacific paradox, in which efforts to expand shifting cultivation field systems lead to deforestation and environmental degradation on small, dry islands. However, despite the risk of environmental collapse, Marquesans succeeded in maintaining both their forests and a thriving human population. How did they adapt to an environment that is too dry for irrigated agriculture, and where, as on Easter, shifting cultivation is unsustainable? The solution was development of a food production system focused on arboriculture. By relying on arboriculture rather than shifting cultivation, Marquesans minimized the use of fire in their fields, as well as the danger of accidental fires, the damaging effects of which could not be tolerated over the long-term. Marquesans introduced most of the cultivated plants comprising the typical Pacific Islands ‘‘transported landscape’’ (Kirch, 1984). They further transformed the vegetational environment by forest replacement, the replacement of native trees with useful introduced tree species (Rolett and Diamond, 2004). Marquesan arboriculture centers around breadfruit, a tree crop that was likely domesticated in New Guinea and which Pacific Islanders introduced to most of the islands they settled (Yen, 1990) (Fig. 5). Arboriculture, also including cultivation of the Tahitian chestnut and various sweet fruits, is a component of most Pacific Island economies but it reached its apogee in East Polynesia, especially the Marquesas. Breadfruit is a seasonal crop but it can be stored in pits where, through a process of anaerobic fermentation, the starchy fruit turns to a sour paste that remains edible for years, even decades, as long as the pit is sealed (Rolett, 1998, p. 34). Although breadfruit is dominated by seeded varieties in the western Pacific, Polynesians selected for seedless varieties because these are best suited for making the fermented paste. Marquesans recognize at least 33 varieties of breadfruit, almost all of which are seedless (Christian, 1910, p. 208). The central
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discussed here is comforting because it shows that fundamental environmental crises faced by the global community today (the shortage of natural resources and human-induced environmental degradation) are ones which Polynesians, living in extreme isolation, also faced and survived. Our formula for success must surely involve avoiding the obvious causes of failure, together with innovation, and long-term resolve. Acknowledgments I am grateful to Yoshinori Yasuda for stimulating my interest in sustainable environments and for inviting me to the symposium at Lake Towada in Japan where an early version of this paper was presented. I thank Peter Matthews for valuable comments on the manuscript. References
Fig. 5. Breadfruit tree growing in the Marquesas Islands (photo by B. Rolett, December 1985).
role of breadfruit in the Marquesas is well described by an early American visitor, Captain David Porter. Porter wrote: The breadfruit tree is every thing to the natives of these islandsy Describe to one of the nativesy a country abounding in every thing that we consider desirable, and after you are done, he will ask you if it provides breadfruit. A country is nothing to them without that blessing, and the season for breadfruit is the time for joy and festivity. (Porter, 1822, pp. 54–55) With forests providing their main source of food, Marquesans avoided the need to rely on shifting cultivation. This adaptation created two benefits. Marquesans were not forced to sacrifice their forests in order to develop and expand their subsistence economy. They also reduced the risk of accidental fires by minimizing the practice of burning fields. 4. Epilogue The formula for sustainability on small, dry islands involves avoiding agricultural strategies associated with fire, while shifting to a reliance on irrigated pondfields or arboriculture. Success was essentially a result of avoiding the continuous expansion of shifting cultivation field systems and the use of fire. The history of Easter Island differs in comparison with that of most other Pacific Islands because its environment is particularly fragile and there was no option for either irrigated agriculture or arboriculture. Knowledge gained from the case studies
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