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By Root 2068 0

rotten logs, and chicken manure as mulches and fertilizers to the soil surface. They dug ditches around fields to lower the watertable and prevent waterlogging, and transferred the organic muck dug out of those ditches onto the soil surface. Legume food crops that fix atmospheric nitrogen, such as beans, were rotated with other crops—in effect, an independent New Guinean invention of a crop rotation principle now widespread in First World agriculture for maintaining soil nitrogen levels. On steep slopes New Guineans constructed terraces, erected soil retention barriers, and of course removed excess water by the vertical drains that aroused the agronomist’s ire. A consequence of their relying on all these specialized methods is that it takes years of growing up in a village to learn how to farm successfully in the New Guinea highlands. My highland friends who spent their childhood years away from their village to pursue an education found, on returning to the village, that they were incompetent at farming their family gardens because they had missed out on mastering a large body of complex knowledge.

Sustainable agriculture in the New Guinea highlands poses difficult problems not only of soil fertility but also of wood supplies, as a result of forests having to be cleared for gardens and villages. The traditional highland lifestyle relied on trees for many purposes, such as for timber to build houses and fences, wood for making tools and utensils and weapons, and fuel for cooking and for heating the hut during the cold nights. Originally, the highlands were covered with oak and beech forests, but thousands of years of gardening have left the most densely populated areas (especially the Wahgi Valley of Papua New Guinea and the Baliem Valley of Indonesian New Guinea) completely deforested up to an elevation of 8,000 feet. Where do highlanders obtain all the wood that they need?

Already on the first day of my visit to the highlands in 1964, I saw groves of a species of casuarina tree in villages and gardens. Also known as she-oaks or ironwood, casuarinas are a group of several dozen tree species with leaves resembling pine needles, native to Pacific islands, Australia, Southeast Asia, and tropical East Africa, but now widely introduced elsewhere because of their easily split but very hard wood (hence that name “ironwood”). A species native to the New Guinea highlands, Casuarina oligodon, is the one that several million highlanders grow on a massive scale by transplanting seedlings that have sprouted naturally along stream banks. Highlanders similarly plant several other tree species, but casuarina is the most prevalent. So extensive is the scale of transplanting casuarinas in the highlands that the practice is now referred to as “silviculture,” the growing of trees instead of field crops as in conventional agriculture (silva, ager, and cultura are the Latin words for woodland, field, and cultivation, respectively).

Only gradually have European foresters come to appreciate the particular advantages of Casuarina oligodon, and the benefits that highlanders obtain from its groves. The species is fast-growing. Its wood is excellent for timber and fuel. Its root nodules that fix nitrogen, and its copious leaf-fall, add both nitrogen and carbon to the soil. Hence casuarinas grown interspersed in active gardens increase the soil’s fertility, while casuarinas grown in abandoned gardens shorten the length of time that the site must be left fallow to recover its fertility before a new crop can be planted. The roots hold soil on steep slopes and thereby reduce erosion. New Guinea farmers claim that the trees somehow reduce garden infestation with a taro beetle, and experience suggests that they are right about that claim as they are about many others, though agronomists still haven’t figured out the basis of the tree’s claimed anti-beetle potency. Highlanders also say that they appreciate their casuarina groves for esthetic reasons, because they like the sound of the wind blowing through the branches, and because the trees provide shade