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Among the most thorough accounts of traditional Pacific agroforestry are those of the south-eastern Solomon Islands by Yen (1974, 1976a, 1976b) and of the Polynesian outlier Tikopia by Kirch and Yen (1982). These works, coupled with Powell's (1976b) study of plant communities and Hendren's (1976) study of Ulawan settlement patterns, provide an excellent basis for understanding agroforestry in the south-eastern Solomon Islands.
The areas studied include the island of San Cristobal (3,500 sq km); the smaller islands of Ulawa and Santa Ana; the Santa Cruz group, including the main island of Nendo (660 sq km); and the islands of Utupua and Vanikolo, the Duff Islands, the main and outer Reef Islands, and the Polynesian outliers of Anuta and Tikopia in the far south-east. The environments of these islands range from the heavily forested interiors of the larger high islands of San Cristobal, Nendo, Utupua, and Vanikoro (which is over 900 metres in elevation) with extensive coastal plains and swampy areas, to smaller volcanic islands, and the coral atolls of Nupani and Nukapu in the outer Reef Islands with very restricted floras.
Agriculture
The dominant agricultural system in most of the south-eastern Solomon Islands is shifting cultivation, with yams (Dioscorea alata and D. esculenta) and taro (Colocasia esculenta) the dominant staples in newly cleared plots. Sweet potatoes (Ipomoea batatas) are commonly planted next in succession. Primary forest is rarely cleared; rather, secondary forests on coastal plains and lower slopes are the most common sites for new gardens. Some inland forest sites are occasionally cleared for yam gardening, including the cultivation of minor species such as Dioscorea pentaphylla, D. nummularia, and D. bulbifera. Yams often occupy drier sites, whereas taro, which is often planted twice before letting the land revert to fallow, occupies wetter areas. Giant taro (Alocasia macrorrhiza) is occasionally planted as a supplementary staple (Hendren 1976; Kirch and Yen 1982; Powell 1976b; Yen 1973, 1976a, 1976b).
Gardens are usually cropped for no longer than three years, with fallows ranging from 6 to 12 years. More permanent gardens of perennials such as Cyrtosperma chamissonis and trees are also found in some areas, such as Nendo. Wetland cultivation of taro and sago palm (Metroxylon salomonense) is practiced in the Duff group. On Anuta and Tikopia, more permanent or intensive systems incorporating cassava into taro-cassava or sweet potato-cassava rotations have displaced yam cultivation.
The greater intensity of land and resource utilization on the small isolated islands of Anuta and Tikopia is evidenced by the great diversity of seasonal surpluses of foods stored using pit-preservation or ensiling by semi-anaerobic fermentation. Herbaceous and tree species thus utilized included breadfruit, Burkella fruit, Ananas and plantains, sago, taro, cassava, Polynesian arrowroot (Tacca leontopetaloides), giant taro (Alocasia macrorrhiza), and giant swamp taro (Cyrtosperma chamissonis) (Yen 1976a). Further evidence of intensification is provided by the existence of walled garden complexes (hatarau or pwainua) and non-irrigated terraces on Ulawa (Hendren 1976) and stone-walled terraces on Anuta (Yen 1976a).
Agroforestry and arboreal components
All agricultural and land-use zones have major arboreal components. The main species found in villages and home gardens, in permanent village tree groves, and as protected or deliberately planted intercrops in coastal and inland food gardens include coconut palms (the most common intercrop), a wide range of banana and plantain cultivars (Musa cultivars), breadfruit (Artocarpus altilis), sago palm (Metroxylon salomonense), the nut trees Canarium spp., Barringtonia edulis, Inocarpus fagifer, and Terminalia catappa, Burkella obovata, edible pandanus (Pandanus dubius), Malay or mountain apple (Syzygium malaccense), oceanic Iychee (Pometia pinnata), the hogplum or Polynesian vi-apple (Spondias dulcis), Gnetum gnemon, edible figs (Ficus spp.), and the betel-nut palm (Areca catechu). More recent introductions include mango (Mangifera indica), citrus trees (Citrus spp.), and papaya (Carica papaya). Of the non-food species, Ceiba pentandra is very common.
Other less common or locally important species found planted or protected in gardens and tree groves include Antiaris toxicaria, Sterculia sp., Semecarpus sp., and Corynocarpus cribbeanus, with Sterculia and Semecarpus being planted in breadfruit groves as living ladders. Species found around former inland settlement sites include Areca catechu, Burkella obovata, Terminalia catappa, Gnetum gnemon, Corynocarpus cribbeanus, and Cordyline fruticosa and Cyathea sp.
Shrubby or herbaceous supplementary food species intercroppped in food gardens and planted in villages and home gardens include hibiscus spinach (Hibiscus manihot), sugar cane (Saccharum officinarum), Cordyline fruticosa (also represented by cultivars of ornamental and magical or ceremonial importance), edible panax (Polyscias fruticosa and P. scutellaria), and maize (Zea mays) and non-food species such as Pandanus spp., Euadia sp., Alpinia sp., Codiaeum variegatum, Gardenia sp., Halfordia sp., and tree ferns (Cyathea sp.). Species commonly planted along garden borders or as hedges include vegetatively planted Barringtonia edulis cultivars, Ananas and plantains, sugar cane, Cordyline fruticosa, and Polyscias spp.
For many of these species, both wild (or feral) and cultivated forms are recognized, with numerous cultivars or varieties specified for the more common species. For example, there are 13 varietal forms of coconut, 33 banana or plantain cultivars, 18 breadfruit cultivars, 3-5 cultivars each for Canarium spp., Pometia pinnata, Barringtonia edulis, and Burkella sp., and at least 2 cultivars each for Terminalia catappa, Metroxylon salomonense, and Gnetum gnemon. The wide range of arboreal husbandry strategies includes deliberate planting of seeds, shoots, branches, and other vegetative parts, the transplanting of self-sown seedlings, and their protection in fallows. Of particular interest is the hypothesis that many trees that grow wild elsewhere (e.g. Burkella obovata, Pometia pinnata, and Calophyllum inophyllum) have been domesticated or semi-domesticated in the southeastern Solomon Islands because of the "accent on trees there" resulting from "an intensification of attention on the gathering aspect of subsistence economy." This focus on arboriculture seems to be Melanesian (that is, nonAustronesian) rather than Austronesian or Polynesian (Yen 1974).
None the less, arboriculture in the definitely Austronesian areas, such as on the Polynesian outlier of Tikopia, also reflects great agroforestry sophistication, possibly as a result of continued contact with Melanesia. Because of the unusual richness and significance of the Tikopian orchard tracts, the description of them by Kirch and Yen (1982, 38-39) is provided at some lenght:
The orchard tracts are not exclusively devoted to productive trees. Rather, they mimic the mixed nature of the low-altitude forest associations typical of the Solomon Islands flora, not only in tree species, but also in the subcanopy. These artificial associations are exemplary of the multi-storey forms of cropping sometimes recommended as innovations for modern agricultural development in the Pacific, but which actually already exist as indigenous adaptations (Ward and Proctor 1980), albeit sometimes erased by the adoption of commercial cropping modes. A characteristic Tikopia orchardholding has a lower planted storey of Cyrtosperma, which, it should be noted, is adapted well beyond its "swamp taro" environment. Bananas generally form the second storey upward, but in scattered distribution, their situation being favored by more open portions of the canopy. The vines of Piper belle may climb to quite prodigious heights on trees, but are generally kept in control by constant picking for betel chewing, while the yams . . . climb to the upper reaches, depending on season and time of planting. The density and diversity of the middle storey is compounded by the presence of Antiaris and Gnetum trees, the occasional cycad, and the saga palm at different stages of growth before flowering or maturity, when its height may reach 20 meters. The bulk of the canopy, generally below that height, consists of the orchard trees proper- breadfruit, Eugenia, lnocarpus, Spondias, and the occasional Calophyllum. On the flatland and at lower altitudes (below 50 meters above sea level), this list is often enriched by Canarium, Burkella, Terminalia catappa, Barringtonia, and Pometia.... The coconut, important not only as a food source but also for its multiple industrial uses, does not form the familiar belts of Pacific island strands; rather it is distributed on Tikopia throughout the orchard gardens, in all but the highest sections of the island to protrude above the canopy of economic trees.
More monocultural smallholder coconut plantations, the main source of cash income, extend from coastal plains up to an elevation of 22 metres. Breadfruit and bananas or plantains are planted in almost monospecific groves or patches on the coastal plains and near active garden areas.
When clearing secondary vegetation for new gardens, most of these species are preserved, although some - such as Pometia pinnate and Ficus spp. - may be severely pruned or pollarded to open up new garden areas to sunlight and to provide additional organic material or ash. Self-sown seedlings of these species are also protected through selective weeding and are allowed to regenerate as part of the fallow vegetation.
Pioneer species, which are abundant in secondary and open disturbed forest and common in young regrowth in still-productive gardens on most of the larger islands, include Macaranga, Trema, Pipturus, Ficus, Glochidion, Acalypha, Piper and Euodia spp., Morinda citrifolia, Kleinhovia hospita, and Hibiscus tiliaceus. Species more prominent in mature secondary or older regrowth forests, ready for reworking into gardens, include many of the commonly cultivated species such as Pometia pinnata (often as a dominant), Canarium spp., Artocarpus altilis, Syzygium spp., Burkella obovata, Antiaris toxicaria, Spondias dulcis, wild varieties of Areca catechu, stands of bamboo (possibly including both Schizostachyam glaucifolium and Bambusa spp.) along with the indigenous species, Alphitonia incana, Securinega flexuosa, Pterocarpus indicus, Semecarpus sp., and Dysoxylum, Ficus and Elaeocarpus spp. Less common secondary forest species include Stemonurus sp., Boerlagiodendron sp., Horsfieldia spicata, Nauclea orientalis, Garcinia sessilis, Cryptocarya medicinalis, Pimleodendron amboinicum, with common understorey species in mature fallow forest including Cordyline fruticosa, Fagraea racemosa, Euadia, Psychotria, Calophyllum, Codiaeum, Dracaena, and Pseuderanthemum spp. (Powell 1976b).
The climax or only partially disturbed inland forests of the larger islands provide the main hunting and gardening reserves; the dominant trees are Agathis macrophylla, Terminalia calamansanai, Calophyllum vitiense, Dacrydium elatum, and Albizia falcataria with Campnosperma brevipetiolata being common in more disturbed areas.
Protected areas of coastal strand, mangrove, or coastal plain and lake-shore vegetation can also be seen as integral to traditional agroforestry strategies in the south-eastern Solomon Islands. Species commonly found in these areas include Calophyllum inophyllum, Pandanus tectorius, Casuarina equisetifolia, Hibiscus tiliaceus, Terminalia catappa, Inocarpus fagifer, Cerbera manghas, Barringtonia asiatica, Barringtonia racemosa, Heritiera littoralis, and Intsia bijuga. Less common species include Thespesia populnea, Cordia subcordata, Hernandia nymphaeifolia, Tournefortia argentea, and Pisonia grandis.
The "extension of strand vegetation" inland was encouraged through the tending of coastal tree species of value for consumption and industrial use. There were also plantings of feral genera such as Pandanus, Barringtonia, and Terminalia, and species such as Calophyllum inophyllum (Yen 1976a). C. inophyllum, in particular, was commonly planted in the main Reef Islands and domesticated and seed-sown in large-scale plantings (aururakau o ngatai) for the purpose of shore-line stabilization and in garden areas up to 300 metres on Tikopia, with Casuarina equisetifolia, H. tiliaccus, Ochrosia sp. (Neisosperma oppositifolia?), and Pipturus sp. reportedly being semi-domesticated and planted inland and for coastal stabilization.