THE seasonally wet tropics are defined here as those that receive from 800 mm to 1,500 mm of rain a year, of which over 70 per cent falls during a wet season of from 3 to 5 consecutive months. The dominant vegetation is savannah woodland, and the ground cover, of tall to mid-height annual and perennial grasses, is characteristically sparse at the onset of the convectional downpours which herald the wet season, but increases rapidly once the soil water-content is replenished.