ABSTRACT

This paper focuses mainly on the humid tropical and parts of the subhumid tropical subregions of Chang & Lau (1986), associated with the narrow geographic band of about 5° to 7° north and south of the equator. In the humid tropical regions, where precipitation exceeds evaporation for at least 9.5 months per year, Tropical Rain Forest (TRF) is the dominant vegetation in undisturbed conditions and tropical cyclonic influences are absent (Lai, 1987). Occasional reference, however, will be made to the hydrological characteristics of the wet-dry tropical region. The gaps in research knowledge related to the water balance, erosion and sedimentation and change in land-use are addressed. Brief reference is also given to the applications of remote sensing and geographic information systems, and to the problems of scale.

INTRODUCTION

The climax vegetation of the humid tropics regions is tropical rain forest (TRF), which is a diverse and complex system that occupies approximately 10% of the world's area (Golley et al., 1975). The vegetation of TRF is characterized by high plant biomass, concentration of nutrients within the plant biomass and efficient and rapid rates of nutrient recycling which enable this eco-system to sustain itself. The vegetation biomass ranges from 200 to 400 t ha−1 and the number, size and height of tree species within a TRF are highly variable and diverse. In addition, mature TRF has a multi-storey canopy of different strata (Lai, 1986) with a leaf area index (LAI) commonly reported as ranging from 7 to 28.