Abstract

Environmental and human factors affecting savanna and grassland in southern Papua are examined. The study indicates that the distribution of these formations is not wholly consistent with prevailing environmental conditions; this reflects the fact that the savanna and grassland, over at least part of their extent, are man-made, having formed as a result of the combined effects of shifting cultivation and burning. Whether the savanna and grassland originated wholly in this way, however, is not clear; their development may also have been influenced by past climatic fluctuation. At the present time, the maintenance of the formations, as distinct from their origin, appears to be attributable to man's activities in burning. THE vegetation of the Territory of Papua and New Guinea is predominantly tropical and montane forest, but is locally replaced by savanna and grassland. The latter formations have been examined in the Sepik valley (Reiner and Robbins, I964; Haantjens et al., I965), in northern Papua (Taylor, I968) and in the New Guinea highlands (Robbins, 1960; Brookfield, 1964) and are considered to be the product of human activity. In southern Papua the situation is less clear; Van Royen (I963) suggests that much of the savanna and grassland in this dry region has originated from and is maintained by natural fires, although he accepts that some man-made extension of the formations has occurred; in contrast, Heyligers (1965, 1966) believes that the savanna and grassland are largely caused and maintained by man-made fires. In the present study, the origin and present status of the formations in southern Papua are re-examined, with parrticular reference to the relative influence of climate, terrain, soils, fire and shifting cultivation. PHYSICAL ENVIRONMENT In the vicinity of Port Moresby, the Papuan peninsula is some I 50 km in breadth and comprises a central mountain range, rising in places to 4000 m in height and flanked by a lower coastal belt of variable width and topography. The Port Moresby region of southern Papua has been described by Mabbutt et al. (1965) and the following major physiographic units may be identified: coastal hills and plains, the foothill zone, and the upland zone. The coastal zone comprises several hill ranges, rising 200-400 m in height, which are separated by alluvial plains and broad river valleys. The area is strongly folded and faulted (Glaessner 1952); upstanding areas commonly consist of cherty limestone, while mudstone, siltstone and tuff are also encountered. Inland, the foothill zone displays more relief, and gabbro and other intrusive rocks occur. Finally, some io km inland there is an abrupt transition to the upland zone or Sogeri plateau, which forms an extensive basin shaped feature at a height of 500-I000 m, and consists of gently dipping volcanic rocks, principally agglomerate, tuff and lava. The climate of the area varies principally in accordance with relief (Fig. i). The coastal zone is relatively dry with an annual rainfall of 950-I600 mm, and experiences a marked seasonality of rainfall. The mean annual temperature is approximately 27°C. Inland, rainfall totals increase; in the foothill zone, they attain I600-2500 mm per annum, and seasonality is less pronounced than in the coastal zone, while on Sogeri plateau rainfall is in the range 2200-3500

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