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On most of the larger islands of Melanesia, sufficient land and relatively low population densities allow for the practice of extensive agricultural systems within largely forested landscapes. Human settlement and use of these lands have caused a humanization, taming, or "agriculturalization" of the forest. Although there is variation from place to place, the basic agricultural strategy consists of felling or ringbarking some trees and clearing the underbrush while at the same time protecting selected tree species that will remain or be allowed to regenerate as part of the garden of deliberately planted short-term crops and domesticated trees.
In most cases, the debris from forest clearing is allowed to dry and is then burned before or during planting, although in some areas such as on the Great Papuan Plateau in Papua New Guinea (Schieffelin 1975), on the Weather Coast of Guadalcanal, and in the upper Wainimala River area of Tailevu Province, Fiji - burning is discouraged. The debris is allowed to decay around emergent crops, thus retarding soil erosion and enhancing the development of the soil structure and the accumulation of organic matter.
The trees that have been preserved usually have some utilitarian value, such as provision of fruits, nuts, edible leaves, medicines, or wood for special purposes; or trees may be left intact or not weeded out because they improve the soil (e.g., the leguminous Albizia falcataria) or serve as habitats for desired prey such as birds of paradise, pigeons, or flying foxes (fruit bats). When such favoured trees are left unfelled on new garden sites, they are often pruned or pollarded to open up the ground to sunlight, to add additional organic material to the soil, or to provide support for climbing or sprawling crops. Thus, the practice of the classic system of shifting cultivation of gardens in forest results not only in the maintenance of soil fertility on garden sites but also in the development of a humanized forest fallow that itself contains many trees of economic and cultural significance.
The case-studies of Melanesian agroforestry systems presented in this chapter and chapter 4 are drawn from research carried out in various parts of Papua New Guinea, the Solomon Islands, Vanuatu, and Fiji (see map p. 36); the studies illustrate the range of variation possible within this general pattern. Some of the examples described are from areas of relatively low population density (Nduimba Basin in the highland fringe of Papua New Guinea and, in chapter 4, Namosi and Matainasau in Fiji); others are from areas of fairly high density (Buma on Malaita in the Solomon Islands and, in chapter 4, Tanna in Vanuatu). Not included in the Melanesian case-studies, except by inference in the discussion of the highland fringe of Papua New Guinea, is a description of the intensive, quasi-permanent sweet-potato cultivation of the densely settled Papua New Guinea Highlands, where labour-demanding tillage in grasslands is an important aspect of cultivation. But even here, where the forest has largely been replaced by anthropogenic grasslands, trees remain significant. Groves of Casuarina provide wood for fuel and fencing and serve as a planted, soilenriching fallow; Ficus dammaropsis (the "highland breadfruit") provides edible leaves; planted Pandanus conoideus is important nutritionally at midelevations and also in forested areas; and Pandanus julianettii and P. brosimos, which grow spontaneously or as quasi-domesticates in the remaining high-elevation forests above the zone of cultivation, provide oil-rich nuts that are an important supplementary food.
Clarke's (1965) comparative study of the intensification of shifting agriculture in highland Papua New Guinea provides information on variations between the agroforestry systems practiced by people of the highland fringe of Papua New Guinea.
When studied in the mid-1960s (Clarke 1971), the Maring people of the Nduimba Basin numbered about 150 and occupied several square kilometres of mountainous land adjacent to an immense stretch of unoccupied rain forest on the northern slopes of the Bismarck Range. The population density was low- approximately 12 persons per sq km. Within their occupied territory, with elevations centred around 1,000 metres, no more than two per cent of the forest cover had been converted to grassland. In these few areas, the dominant species were Imperata cylindrica and Ischaemum digitatum, both of which are common components in the early stages of the Nduimba Basin plant succession that leads from cleared garden to well-developed secondary forest. Furthermore, the presence in the grasslands of pioneering trees such as Dodonaea and Alphitonia and tree ferns also points to the transient dominance of the grasses.
The comments of the people of the Nduimba Basin support the botanical evidence with respect to lack of pressure on the land. When asked why they had given garden land or usufructuary rights to outsiders, a frequent reply was: "We are a small group, and we have abundant land; therefore we give land away to friends and kin" (Clarke 1965, 348).
Even when compared with other types of simple shifting cultivation, the system in the Nduimba Basin is remarkably casual. Gardens are started sporadically throughout the year; part of the cut debris is usually burned, but the burning phase may be omitted if the weather remains wet. Most men clear their plots in secondary forest; a few of the "very strong men" sometimes make a clearing in the primary forest, a process that is more work than cutting the slenderer trees of the secondary forest. Low bush and the limited grasslands are never used for gardens. No tillage - in the sense of turning or working the soil - is practiced. Neither irrigation nor ditching is present or necessary. The planting tool is a simple wooden dibble. The polycultural mix of many species of tuber and fruit- or leaf-bearing crops that are planted in the gardens provides a fairly good diet, which is complemented by wild plant foods (including wild yams, ferns, nuts, fruits, and leaves) and fish, eels, domestic pigs and fowls, insect larvae, birds, and other wild game from the surrounding forest, fallow areas, and streams.
Maring agroforestry practices come into play particularly when the gardens are left to fallow after the harvest of short-term crops. No fallow cover is planted but, because gardeners deliberately leave tree seedlings in the ground while weeding, the plot is usually well colonized by saplings when cultivation ceases. Additionally, as the harvesting of short-term crops comes to an end, the garden sites are transformed into orchards with major plantings of Gnetum gnemon (fibre, edible leaves and fruit) or Pandanus conoideus (oil-rich mesocarp providing very important supplementary food and condiment) and minor plantings of Artocarpus altilis (breadfruit) and Ficus wassa (bark cloth, edible leaves and fruit). The orchards thus come to be scattered widely throughout Maring territory and provide a valuable supply of materials and foods throughout the year. As they age over several decades, the orchards merge back into secondary forest. Their sites again become available for swidden clearing so that the orchards extend production from garden lands for several decades, while at the same time the land is receiving benefits similar to those gained from fallow under spontaneous secondary forest.
The Maring also recognize unplanted secondary-forest communities as a resource - one that is more valuable than primary forest. Because the secondary forest provides the reinvigorating functions of fallow vegetation that make shifting cultivation possible, it is referred to in the vernacular as the "garden mother." Beyond this important function, the whole secondary zone - which derives from clearing for gardens combined with the protection of tree seedlings during weeding - serves as a foraging zone for domestic pigs and as a hunting ground for the men who pass through it daily on their rounds. The secondary communities also serve as sources of plant foods and materials. The common Alphitonia-Cyathea woodlands provide easily-cut wood for fencing and fuel. In addition, the Cyathea provides edible leaves; and the understorey plants, growing in the light shade, provide cordage, edible leaves, and medicines. The secondary Albizia falcataria community is recognized as most valuable for increasing soil fertility for future gardens, presumably through the usual nitrogen-fixing processes of leguminous plants; Albizia's wood is also valued for carving. Jungle regrowth provides edible leaves as well as wild Musa leaves for wrapping materials and for clean surfaces for food preparation. In other words, not only does the temporal alternation of forest fallow with gardens make the gardens produc five, the successional stages of the forest are themselves valuable for other purposes (Clarke 1971, 60-64).
The people of the Nduimba Basin are not oppressed by garden work. Even the women, who do most of the steady work of weeding and harvesting, frequently take a day's vacation and eat food gathered on the previous day or collect snacks of sugar cane from their nearest garden. Food shortages and crop failures are unknown, and when the gardens are abandoned they contain considerable amounts of unharvested produce.
Kompiai is the name given now to a territory on the southern slopes of the Bismarck Range (Jimi River valley) occupied by the Kauwatyi clan cluster, a group that numbers about 850. The average population density at Kompiai is 29 people per sq km, more than double that in the Nduimba Basin. At Kompiai, retrogressive succession of the vegetation is more advanced than in the Nduimba Basin, which is about 16 km distant. Perhaps as much as 20 per cent of the Kauwatyi land is grassland containing genera such as Themeda, Arundinella, Ophiurus, and Eulalia, which are thought to be indicative of degraded sites. Kompiai has a smaller percentage of primary forest than the Nduimba Basin. On average, the secondary forest at Kompiai is younger, and much of it is floristically less complex; large areas are covered by almost pure stands of the weed tree Dodonaea viscosa - a type of simple regrowth that is absent from the Nduimba Basin.
This circumstantial evidence of an intensity of land use greater than that of the Nduimba Basin is compatible with what the Kauwatyi say about their land and with their quite unusual action in the mid-1950s when they attempted to make gardens in the territory of a defeated neighbour before certain prescribed ritual procedures had taken place. Such an attempt almost certainly indicated considerable pressure on the land because, in this part of Papua New Guinea, the extension of territory is scarcely ever an immediate result of warfare.
The gardens at Kompiai look almost like those in the Nduimba Basin: there is neither tillage, irrigation, nor any attempt to improve soil drainage; nor are the grasslands used for gardens except on rare occasions. The methods of planting, the agricultural tools, and the "messy" intermixture of garden plants are the same in both places. The crops grown are the same, too, but the proportions are different. At Kompiai, sweet potatoes become relatively more important among the starchy staples grown - an indication of the beginning steps toward the very heavy dependence on that crop that characterizes the areas of highest population density in the central highlands of Papua New Guinea, where fields are used almost continuously and forest fallow is wholly absent. The orchards of Pandanus conoideus, Gnetum, and breadfruit are rarer at Kompiai than in the Nduimba Basin, and game is scarcer.
The intensity of harvest and the age and type of fallow cover also vary between the two places. Native informants all agreed that the Kauwatyi harvest their gardens more thoroughly than the inhabitants of the Nduimba Basin. Moreover, when the Kauwatyi decide that an old garden is ready for fallow, they bring their pigs to the plot to root for the small tubers that still remain in the ground. In the same situation, the people of the Nduimba Basin simply abandoned the plot; if the pigs find it, well and good; if not, it does not matter. Doubtless, if the pig herd of the Nduimba Basin were to increase, the Kauwatyi custom would be adopted.
Although fallow periods are shorter at Kompiai than in the Nduimba Basin and consequently there is less well-developed secondary forest, the Kauwatyi habit of planting or encouraging quick-growing Casuarina oligodon trees in old gardens may slow the decline in soil fertility associated with decreasing lengths of fallow between periods of gardening. Interestingly, although the people say that the soil under Casuarina groves is better than that under other types of fallow, the main motive for planting the trees seems to be to obtain wood for fences, fuel, and house construction. Despite the value placed on the trees, the people's efforts to establish groves of Casuarina are haphazard; if the bare ground of a new garden develops Casuarina seedlings, the gardener cherishes them; but if seedlings do not develop, he does not always transplant seedlings into the garden (Clarke 1965, 349-352).
In contrast, not far away in the upper Kaironk Valley - where population density is even higher, and spontaneous forest almost absent except on the cloudy mountain crests - planting of Casuarina as a fallow cover for gardens is much more systematic. Groves of these graceful trees dot the grassy landscape, and a high percentage of the gardens are planted beneath pollarded Casuarina. Despite the soil improvement brought by these nitrogen-fixing trees, land degradation has proceeded in the Kaironk to the point where labour-intensive tillage is required to maintain soil fertility, and sweet potatoes (which require a less fertile soil than Colocasia taro or yams) are far more important than at Kompiai or in the Nduimba Basin.
Implications of increasing agricultural intensification
The variations between the agro-ecosystems of the Nduimba Basin, Kompiai, and the Kaironk Valley can be interpreted as a sequence of increasing agricultural intensification. The consequences of a decline in the amount of well-developed natural forest because of extended cropping cycles and shortened fallow periods (caused in part by a recent expansion of smallholder commercial coffee planting and beef cattle production) include an increase in the intensity of garden harvesting, an increasing use of agronomic techniques to maintain soil fertility, a decline in yield per unit labour, and a concentration of effort towards production of the highest-yielding crops (sweet potatoes in the highland New Guinean case). The implications for agroforestry are that, as primary forest and well-developed secondary forest are converted to grassland or impoverished scrub under regimes of increasing population density and shortened fallow, the resources available from forest disappear, and the regenerating "work" done by the forest must be taken over by the human cultivators if an acceptable level of soil fertility is to be maintained. In parts of New Guinea a traditional solution to the loss of spontaneous forests was the creation of artificial forests of Casuarina (or Dodonaea viscosa in some places) to aid soil regeneration and to provide wood for fuel and fencing. Although of great value, such single-species stands of trees did not provide the variety of wildlife habitats or the food, medicine, or other materials found in the more species rich natural forests.
In 1972, population densities on the Weather Coast of southern Guadalcanal, the Solomon Islands, ranged from 1.5 to 26.4 persons per sq km (Chapman and Pirie 1974). Pressure on land was low in the vicinity of Kologhona village, some 10 km inland from Babanakira in the upper Tina River Basin of the Wanderer Bay area. The village, which had a population of approximately 60 in early 1975, had access to extensive areas of alluvial and colluvial soils, steeply sloping garden land covered with secondary forest, and considerable areas of slightly disturbed primary forest along the crests of the ridges and on the steeper slopes.
The two most common subtypes of agroforestry practiced in Kologhona are ago-puka and ago-male. The ago-paka method is practiced in old forest at some distance from the village. All but the biggest trees are felled, after which the debris is piled around the bases of bigger trees and burned. No attempt is made to clear all stumps or level the ground before planting commences. Traditionally, planting was almost exclusively women's work, using digging sticks and hoes; men are increasingly doing more of this work. Yams and Colocasia taro are the most common crops planted in these gardens, although other ground and tree crops are also planted. Fallen trees are allowed to lie in the garden, often placed along contours to retard erosion and to provide for trellising yams and other climbing plants.
In the more heavily cropped alluvial and colluvial soils and gardens closer to the village, the ago-male method is more common. Its practice means the extension of existing gardens into surrounding secondary vegetation by clearing, moving the debris to the side, and planting without burning (Rainbow and Teteha 1983). Sweet potato is the major crop in these gardens, intercropped with yams, taro (Colocasia and Xanthosoma), banana cultivars, and a diversity of other crops, including sugar cane, Saccharum edule, Hibiscus manihot, pumpkin, pineapple, maize, chill) peppers, and tobacco.
Trees with edible fruits and nuts are commonly protected when secondary vegetation is cleared, or they are planted amongst crops. Trees so treated include breadfruit, coconut, betel-nut, papaya, Citrus spp., Canarium spp., Inocarpus fagifer, Barringtonia edulis, Syzygium malaccense, and Ficus copiosa. Other useful tree or tree-like species maintained in gardens include Pandanus tectorius, kapok (Ceiba pentandra), and sago palm (Metroxylon salomonense) and
Heliconia indica, both of which are found mostly in poorly drained areas close to the river. In fallow areas, the commonest pioneer species are Kleinhovia hospita, A lstonia spp., Ficus spp., and Macaranga aleuritoides. Wild foods - including wild yams (Dioscorea spp.), a range of ferns, and other wild greens - and animal foods are either preserved through selective weeding or occur in fallow and secondary vegetation.
Despite increasing population pressure, the preservation of trees as part of an integral agroforestry system has continued. However, increasing pressure by the government to expand monocultures of copra or cocoa and the smallholder production of beef cattle, with no emphasis on the maintenance of arboreal diversity, is accelerating agrodeforestation on the Weather Coast and will play a major role in the decline of arboreal diversity and self-sufficiency and the loss of knowledge of traditional agroforestry systems among young agroentrepreneurs.
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