The instability of the tropical ecosystem in New Guinea

The tropical ecosystem has been considered by many authorities as a stable vegetation type that, in some areas, has ‘existed uninterruptedly since a very remote geological time’ (Richards, 1952). The long term stability of rainforest ecosystems was first questioned when studies showed that there was a marked contraction of rainforest areas in the tropics during Pleistocene times (Flenley, 1979). Within New Guinea two major effects are reported: altitudinal fluctuation of the major vegetation zones at higher altitudes, as described by Flenley (1972), Hope (1976), Powell (1970), and Walker (1970); and a decrease in precipitation. As a result of the lower rainfall during the Pleistocene era (17,000—14,000 yrs BP) extensive areas of New Guinea were characterised by a very dry savanna type climate (Nix & Kalma, 1972). This is still reflected in the distribution of savanna elements in the present vegetation, in both lowland and lower montane areas. However, extensive disturbances are by no means restricted to the Pleistocene times. Studies in New Guinea show that the environment has been recently subjected to major disturbances caused by natural disasters. These phenomena are often easily plotted from aerial photographs and by using remote sensing techniques. An understanding of environmental instability is important, not only for the interpretation of the structure and floristics of the extant vegetation, but is also of major importance in the management of the tropical environment in New Guinea.