LIFEFORM DISTRIBUTIONS OF WOODLAND PLANT-SPECIES ALONG A MOISTURE AVAILABILITY GRADIENT IN AUSTRALIA MONSOONAL TROPICS

A series of vegetation sites was established in Australia's Northern T erritory between Darwin and Tennant Creek, a distance of approximately 1000 km and 7 degrees latitude (12 degrees 30'-19 degrees 30'S). This region encompasses a strong environmental gradient in mean annual moi sture availability (450-1600 mm) whilst remaining within a predominant ly summer monsoonal rainfall regime. All sites are within eucalypt-sav anna habitats on lighter textured soils (sands-loams). Major changes i n family and species representation occur at approximately 16-17 degre es latitude, supporting findings of other workers. Within these eucaly pt-savanna communities, the percentage of annual species is consistent ly around 30% regardless of latitude. However, the distribution of res ource allocation strategies used by perennial plants exhibits distinct latitudinal trends. The proportion of deciduous and seasonally perenn ial species declines with latitude whilst suffrutescent shrub species become increasingly abundant. Species possessing root structures adapt ed for storage purposes appear to be limited to latitudes north of 15 degrees S.