INTRODUCTION

The cultivation regimes of the rugged central highland region of the mountainous interior of New Guinea, and their environmental relations, are the intriguing subject of this book. In some gardens, people practice classic shifting cultivation, clearing them for one, or possibly two crops, and then abandoning them to natural regrowth for many years. Other plots they keep under more-or-less permanent cultivation for decades, with occasional, relatively brief periods of grassy fallow between some cultivations. And between these extremes, they culivate a range of plots for varying periods of time. When they break new ground for a garden, the farmers often cannot say how long it will remain under cultivation. They plant it and see how their crops fare. So long as yields are respectable, and the location of the garden convenient, they may continue to cultivate it indefinitely. All cultivations, whatever their productive life, are farmed using the same technology and procedures.

Several strands weave through the book. One is an account of a montane New Guinea ecology, framed around the soils that have culminated there from long-term interaction between the various factors that comprise the region’s natural environment. Another is the attempt made to convey how the local people residing in the area perceive of their natural surroundings and contrive to manage them. Here the study relates ecology, particularly soils, to their intriguing horticultural tradition where they cultivate some sites semi-permanently within the context of a nominal shifting cultivation strategy. A further strand concerns the ecology of their staple crop sweet potato, which occupies a significant place in this agricultural regime. This electronic publication contains detailed data on soils, analysed in the book (which would have proved prohibitively costly to publish conventionally) They are reproduced here to give a comprehensive record.

A remarkable feature of the Highland farming system is that inputs for all gardens are internally derived, whatever their age. Nothing is added to sites from outside during their productive lives. When cleared initially of natural vegetation, all cut material of suitable size is burned; other than that used in enclosing the plot (for fence stakes, log barricades or whatever). Nutrient elements locked up in the vegetation are returned quickly to the soil in a form in which they may be rapidly further broken down for plant uptake. When a plot is recultivated and planted, all weedy regrowth and any remaining crop residues are composted into the earth mounds which characterise cultivation of the region’s staple sweet potato crop. Similarly, if a site is left fallow for a longer period, until grassy and herbaceous vegetation cover it densely, the coarse grasses and associated herbs are uprooted and incorporated into mounds during recultivation, either green or burnt, as compost or ash.

The literature on tropical farming systems would prompt us to predict a decline in the productivity of sites over time due to nutrient losses, weed proliferation, soil depletion through erosion, and so on. If no manure or other amendments are added to gardens from outside, we should anticipate a steady decline in soil fertility. Indeed some sites, far from experiencing a decline in staple crop yields, as the accepted ecological model of low-input agriculture predicts, experience the reverse and improve with time under cultivation, with increases in yields. We may take the decrease in the variety of crops cultivated on a site after it has been planted once or twice, to reflect some change in soil nutrient status. When first cleared and cultivated, gardens support a wide range of crops, including various tubers, cucurbits, beans, many green-leafy ‘spinach’ crops, plus a range of longer term crops (like bananas, sugar cane and pandans), together with various recently introduced plants (including brassicas, onions, and tomatoes among others). After one or two cropping cycles, a markedly narrower range of crops is grown, with many gardens passing under a virtual monocrop of sweet potato, perhaps with some longer term crops here and there, and the occasional patch of pumpkin, edible pit pit and acanth greens.

The farming practices of these people seem to contradict widely accepted assumptions about traditional agriculture in the tropics. How can this be so? How are they able to continue with an agricultural system that features repeated cultivation of sites, with minimal or no fallow breaks and no outside amendments, without a catastrophic decline in productivity? How is it that the reverse sometimes occurs and crop yields improve?

It is to these and related questions that this study addresses itself. It assumes that the ecology of the Highland region features prominently in any answers, particularly local soil conditions and management practices. It is structured around an investigation of the natural environment, with an indigenous perspective. And it focuses on the soil as the natural resource central to any agricultural system, building upon an ecological analysis to advance understanding of it. It presents this in an ethno-environmental context, that is one which attempts to convey something about local people’s perspectives, in addition to those of environmental science.

The supplementary data are divided between the following pages:

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