Lifeform distributions of woodland plant species along a moisture availability gradient in Australia's monsoonal tropics

Abstract

A series of vegetation sites was established in Australia's Northern Territory between Darwin and Tennant Creek, a distance of approximately 1000 km and 7° latitude (12°30'–19°30'S). This region encompasses a strong environmental gradient in mean annual moisture availability (450–1600 mm) whilst remaining within a predominantly summer monsoonal rainfall regime. All sites are within eucalypt-savanna habitats on lighter textured soils (sands–loams). Major changes in family and species representation occur at approximately 16–17° latitude, supporting findings of other workers. Within these eucalypt-savanna communities, the percentage of annual species is consistently around 30% regardless of latitude. However, the distribution of resource allocation strategies used by perennial plants exhibits distinct latitudinal trends. The proportion of deciduous and seasonally perennial species declines with latitude whilst suffrutescent shrub species become increasingly abundant. Species possessing root structures adapted for storage purposes appear to be limited to latitudes north of 15°S.