Soils and Cycles

Abstract

Soils are an integral part of the landscape; regional variations cannot be understood unless the soils are seen in their physiographic setting. Landscapes form as a result of complex and interacting geological forces that, on the one hand, create different ‘landforms’ through volcanism, tectonics or sedimentation, and, on the other, destroy them through weathering and erosion. These latter processes are greatly influenced by climate, vegetation cover and by the actions of man. The science of landforms is called geomorphology, as defined in a delightful textbook by Sparks (1972). Geomorphology helps us to correctly interpret maps, air-photos, satellite imagery and field observations; it gives insight into the formation, age and stability of landscapes and to some extent also provides clues to their future. Leafing through Löffler’s book, Geomorphology of Papua New Guinea (1977), one quickly becomes convinced of the importance of geomorphology in the study of rain forests. The book contains fine pictures of the Fly River and its surrounding crackle-like area of 140 × 125 km, made up of a disarray of ridges under dense primary forest. It also shows rain forests from which gruesome limestone peaks protrude (‘broken bottle country’ is the local name), the wide and tranquil lower reaches of the Fly River with levees under forest and wide swampy basins, forest on limestone reefs that emerge from the sea and wide barren strips that curve downhill; the landslides. There are close-ups of tree roots washed free of soil by erosion, where in some instances the eroded soil has formed natural steps, and pictures of earth structures, built by worms, which extend above the dead leaves on the forest floor and themselves are exposed to the forces of erosion.