The Tropical Savannas of Northern Australia

Tropical savannas comprise the main environment across the 2 million km2 of monsoonal northern Australia. As with savannas world-wide, Australian tropical savanna vegetation is characterized by a dense C4 grass layer and variably open tree layer. Vegetation structure and composition vary across the gradient of annual rainfall from c. 2000 mm (in the coastal north) to c. 500 mm (inland), with tree cover and height greatest in higher rainfall areas. Unlike most tropical savannas globally, in the Australian tropical savannas, most canopy trees are evergreen, with eucalypts (Eucalyptus and Corymbia species) dominating. Influenced by a long annual dry season, fire is frequent and is a major influence on vegetation, particularly shaping the extent of a shrubby understorey layer. The fauna is highly distinctive-for some groups it is extremely rich and with high levels of endemism, but it lacks native megaherbivores. The Australian tropical savannas have remained extensive and largely intact, with relatively low human population density, little habitat loss, and no known extinctions over the c. 200 years since European settlement. However, some native species are now declining, many invasive species have become pests or weeds, and there is ongoing pressure to modify habitats to allow more intensive development.