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5. Agricultural sustainability and food in Papua New Guinea

Ryutaro Ohtsuka

The sample populations
Agricultural sustainability in low population density areas
Agricultural sustainability in high population density areas
Population increase and agricultural sustainability


Papua New Guinea is located between the equator and 12°S latitude and consists of the eastern half of the large island of New Guinea and the Bismarck Archipelago and many other small islands. The majority of the Papua New Guinea peoples have subsisted on cultivation of non-cereal crops, such as tare, yam, banana, and sweet potato, and/or exploitation of sago palm. One of the most striking human ecological characteristics in this country is seen in different population densities in association with the environments where they have lived and the major foods which they have grown and eaten. Moreover, the diversity of Papua New Guineans' adaptation has recently been accelerated by modernization influences, for instance acceptance and enlargement of cash-crop farming and increased rural-urban migration.

Traditional food-production systems in Papua New Guinea can be broadly classified into four categories: two in the high-altitude zone and two in the low-altitude zone (fig. 1). In the high-altitude zone, sweet potato-dependent agriculture has been dominant in the central Highlands and taro-dependent agriculture in the Highlands fringe. In contrast to the low-altitude zone, the high-altitude zone had long been free from malaria, the most life-threatening disease in this country (Riley 1983), and thus has been more densely populated. More important is the fact that compared with taro cultivators, the sweet-potato cultivators have kept higher population densities due to markedly high productivity of this crop (e.g. Golson 1977; Bayliss-Smith 1985) and their elaborate cultivation techniques (e.g. Waddell 1972). It is also noted that acculturation has progressed more in the sweet potato cultivating area than in the taro-cultivating area (Fell 1987).

Figure 1 - The Geographical Distribution of Four Major Agricultural Types in Papua New Guinea (Modified from King and Ranck 1982), and the Locations of the Four Populations Treated in this Paper (1: Mountain Ok, 2: Huli, 3: Gidra, 4: Balopa)

In the low-altitude zone, cultivation of various crops, such as taro, yam, and banana, has been common in the eastern part of the main island and the islands region, whereas exploitation of sago has been prevailing in the western part of the main island. Sago making is characterised by high productivity per labour time (Ohtsuka 1985; Ulijaszek and Poraituk 1993) but low productivity per total land area owing to the low densities of sago palms which grow in a natural or semicultivated state. Consequently, the population density is lower in the sago-depending peoples than in other peoples throughout the country (Townsend 1971; Townsend et al. 1982; Ohtsuka 1983). Another reason for the low population densities of the sago eaters, in general, comes from delayed acceptance of acculturation influences.

The sample populations

The present paper first summarises the author's observations and findings in four populations studied (fig. 1, table 1) and then discusses agricultural sustainability, taking into account demographic patterns and changes of the people's lifestyle. The Mountain Ok villagers in the Highlands fringe, with less acculturation influence, have carried out taro monoculture and their population density is 1.4 persons/kmē. The Huli in the central Highlands are one of the groups that developed elaborate sweet-potato cultivation techniques, for instance making mounds and/or ditches and planting nitrogenfixing trees (Casuarina spp.) around the gardens. Their population densities are high, ranging from 20 to 150 persons/kmē owing to different soil fertilities (Wood 1985). Because their land is far from the major urban centres, however, the Huli people have scarcely conducted cash-crop farming, contrasting to the bulk of the Highlands populations that have heavily been engaged in growing coffee for export and/or vegetables for marketing at the nearby local centres (Grossman 1984).

Table 1 - The Four Selected Populations for the Intensive Study and Their Basic Characteristics

  Name Altitude Modernization Density (per kmē) Subsistence foods Cash crops
1 Mountain Ok High Low 1.4 Taro Nil
2 Huli High Medium 20-150 Sweet potato (Coffee)a  
3 Gidra Low Medium 0.5 Sago, tubers (Rubber)  
4 Balopa Low Low 30 Tubers Cacao, peanut  

a. Crops in parentheses are raised on a very small scale.

The Gidra form one of the typical sago-eating groups, though they have also grown tubers and bananas in the slash-and-burn gardens. Population density of the Gidra has been about 0.5-2 persons/kmē. They have had acculturation influences in the last several decades but their cash-earning activities have still been negligible. The author, together with his colleagues, has carried out repeated surveys among this group since the early 1970s, so that their long-term adaptation has been clarified (e.g. Ohtsuka and Suzuki 1990). The last group studied is the Balopa, who live in small islands in Manus Province. Their population density has been about 30 persons/kmē. The people, who have raised various garden crops for their subsistence use, began planting coconuts and cacao trees several decades ago, and recently grow peanuts for sale at the markets of Lorengau, the capital of Manus Province. Heavy out-migration is another characteristic of the Balopa people.

Agricultural sustainability in low population density areas

The Gidra have depended for their plant food on sago starch and, to a lesser degree, garden crops. One of the 13 villages, called Wonie, was studied in detail. As shown in table 2, the Wonie villagers' energy intake from plant foods, which account for more than 90 per cent of the total intake, in three different periods, with source foods broken down in accordance with subsistence activities, can be characterised as follows. First, sago starch has provided almost half of the total energy, decreasing gradually throughout the periods; the decrease in dependence on sago is discussed later in relation to the recent population increase.

Table 2 - Energy Intake (kcal) from Plant Foods per Day per Adult Male in Gidra-speaking Wonie Village in Three Time Periods

  1971 1981 1989
Wild plants 117 2 22
Sago 1,827 1,551 1,479
Garden crops
  Taro 439 556 0
  Yam 16 352 772
  Banana 314 76 293
  Sweet potato 11 364 43
  Others 138 243 214
Coconuts 317 10 332
Purchased 0 216 215
Total 3,179 3,371 3,360
(incl. animal foods) (3,323) (3,550) (3,642)

Second, in contrast to the fairly stable output from sago that from various garden crops and coconuts changes over time. Taro had been the most consumed garden crop in this village for a long period, but it had completely vanished from the people's diet in 1989, as a result of the attack of the taro leaf blight (Phytophthora colocasiae), which has been widespread throughout Papua New Guinea (Purseglove 1972; Bourke 1982) and entered the Gidraland in the middle 1980s. The low banana consumption in 1981 reflected heavy damage to the crop by birds, which ate the immature fruit; this type of damage occurs every decade or so to different degrees. Similarly, because immature coconuts were almost completely eaten by rats (Uromys caudimaculatus) for several years from 1981, coconut consumption was negligible at the time. These damages were largely offset by the increased production of yams. On the other hand, the increased consumption of sweet potatoes in 1981 was derived from the introduction of high-yielding varieties in the preceding year through the local agricultural office. However, the villagers' cultivation techniques were not adequate to maintain productivity in the following years.

These year-to-year differences in food consumption, and thus in food production, in Wonie suggest two points relevant to agricultural sustainability, or stability of agricultural production. First, many local staples are not necessarily stable in productivity and are vulnerable to long-term natural environmental fluctuations. This implies, at the minimum, that mixed-crop or multi-crop farming contributes to avoiding deterioration in food production as a whole, as represented by the substitutional role of yams. Second, markedly high yields of sweet potatoes in 1981 (the yields in 1980 were much higher, though quantitative information was not obtained) suggest that the introduction of highly productive varieties or strains of food crops makes drastic increase of food production possible, if the appropriate agricultural technologies are associated.

As shown in table 2, the amount of sago consumed has decreased in Wonie. The author's estimation of their food consumption in the period without manifest acculturation influences, i.e. before the 1950s, reveals that sago consumption was greater (Ohtsuka 1993). The most plausible reason for the decrease of sago consumption and the increase of garden-crop consumption derives from the recent population increase. According to the author's genealogical-demographic analysis, the population increase rate per year markedly increased from only about 0.2 per cent before the 1950s to 2.0 per cent or over at present, a level similar to the national average in the 1970s or 1980s, owing to the provision of health services, immunization practices in particular. The changed population increase rate implies that the population has doubled in the period from 1960 to the present time (Ohtsuka 1986, 1990). To cope with such a high population increase, the Gidra people should have depended more on horticulture than sago exploitation because in their thinly populated land, the garden area can be easily expanded, whereas transplanting of sago palms, the bulk of which grow naturally, cannot meet with great success.

Gradual change of the staple food was also observed in the Mountain Ok villages, from taro to sweet potato (Kuchikura 1990; Ohtsuka 1994; cf. Bayliss-Smith 1985), as demonstrated in table 3, which compares percentage contributions of foods to energy and protein intake between a basically traditional taro-depending village and two villages which accepted sweetpotato cultivation. The cultivation of sweet potato is favourable to cope with increased population because the sweet potato is capable of producing higher yields owing to a short fallow period required and tolerating lower temperatures and poorer soils than tarot The gradual transitions from sago to garden crops among the Gidra and from taro to sweet potato among the Mountain Ok indicate that transfers of agricultural technologies, even those which were developed within Papua New Guinea, tend to elevate productivity in thinly populated and less-modernised societies.

Agricultural sustainability in high population density areas

In densely populated areas, agricultural productivity per land area, in general, has been high. Among the Huli, who have heavily depended on sweet-potato cultivation, their cultivable lands have already been exploited and the fallow period has been extremely reduced, eventually leading to permanent cultivation in many locations. As Wood (1985) suggested, soil erosion became manifest in the Huli land, even in the 1950s. Consequently, it seems difficult for them to maintain present agricultural productivity unless their agricultural system is modified.

Among the Balopa, whose major traditional crops for subsistence use are taro and yam and whose population density is about 30 persons/kmē, cashcrop farming was begun several decades ago. The early efforts were devoted to planting coconuts and then cacao trees. Because of the price reduction of these crops, however, they now grow peanuts, in particular, to sell at the local markets in the nearby town. Their livelihood has been assured by cash-earning agriculture, together with agriculture for subsistence use; in addition, the remittances from outmigrants, most of whom have high-level education and are engaged in qualified jobs. According to the author's observations, soil degradation has not seriously progressed because of the concentrated use of smaller areas for highly productive cash crops, in a sense that the productivity is assessed by not only nutrients contained in foods consumed but also money gained through the cash crops.

Table 3 - Percentage Energy Contributions of Five Categorised Foods in Three Mountain Ok Villages Observed in 1986

  Selbanga Woktembipb Fakobipb
Taro 56.1 13.1 3.6
Sweet potato 32.8 53.8 78.2
Other crops 9.2 30.3 10.1
Wild plants 0.2 2.7 8.1
Animal foods 1.7 0.1 1.5

a. Ohtsuka 1993
b. Kuchikura 1990

The situations of the two groups in the more modernised and densely populated areas suggest that it is possible for the people to survive based not exclusively on subsistence farming but on both subsistence and cash-crop farming. For maintaining earnings from cash cropping, economic development of the nation as a whole and well-planned agricultural policies are indispensable.

Population increase and agricultural sustainability

Figure 2 shows a schematic diagram of changing population and carrying capacity in the four populations. In Papua New Guinea, the population increase rate was markedly elevated by the provision of health services, particularly immunization (Riley and Lehmann 1992). This change took place after the end of World War II, varying in the onset time from location to location but irrespective of the developmental degree of agricultural practices. For instance, among various societies such as the Gidra and the Mountain Ok, mortality rate was drastically improved during the time of low agricultural productivity (Ohtsuka 1993,1994).

The original definition of carrying capacity does not include the role of cash earnings, but the author will use this term as the potential number of persons supported by agricultural products, utilised not only as food but also for cash earning, as represented by a dotted line; the contribution of cash earnings to carrying capacity was observed only in the Balopa among the four populations treated in this paper.

Figure 2 - Schematic Diagrams of Changing Population and Carrying Capacity in Four Populations Studied. All Scales Are Arbitrary, though the Relative Interpopulation Differences in the Population (or Population Density) and the Timing of Change to High Increase Rate Are Based on Empirical Information. The Dotted Line of Carrying Capacity for the Balopa People Reflects Both Subsistence Production and Earnings from Cash and Marketing

The scales of both population and carrying capacity are arbitrary, but the relative inter-group differences in population size and the onset time of change to a higher population increase rate are based on empirical information. Thus, it is noticed that the three populations other than the Balopa have not reached the point at which the cash economy plays a modifying role in carrying capacity.

As mentioned previously, the Gidra and the Mountain Ok peoples have gradually changed their agricultural systems to cope with population increase. Since their population densities are only 1 to 2 persons/kmē, their population numbers have still been lower than the carrying capacity. In other words, there is still room to raise their carrying capacity, mainly through technological changes. In contrast, serious problems took place in the densely populated areas. In particular, the Huli people have elevated their carrying capacity since long ago, mainly owing to the reduction of the fallow period of sweet-potato cultivation to attain high yields per land area in the long run. As a result, the soil fertility in their land has deteriorated. Thus, there is a high possibility that they cannot maintain the present productivity levels in the near future. The situation of the Huli is fairly contrary to that of the Balopa, who have begun cash cropping and whose land has not met with serious degradation.

As a conclusion, the author proposes solutions to cope with the accelerated population increase in the future. For less-modernised and thinly populated areas, the people should change or modify their agricultural systems to achieve more stable and higher productivity. For more modernised and densely populated areas, the people should extend cash-crop farming, simultaneously maintaining subsistence production. Two matters are essential in these processes. One is the introduction of high-yielding crops and elaborate technologies. The other is the enlargement of mixed-crop and/or multi-crop farming. These may be accomplished through the efforts of the local peoples themselves, in addition to the efforts of the governmental and non-governmental professionals. Also needed are national-level efforts to harmonise the development of the rural and urban sectors. Finally, the current population increase rate (2.7 per cent per year in 1990, according to the Population Reference Bureau) should be reduced as shortly as possible; otherwise, any efforts for agricultural development cannot produce fruitful results.


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