Australian Savanna: The World's Most Extensive Tropical Grassland

The tropical savannas of northern Australia — stretching from the Kimberley of Western Australia through the Northern Territory to Cape York in Queensland — constitute approximately 1.9 million square kilometres of tropical grassland and open woodland: the most extensive intact tropical savanna in the world. This vast landscape — crossed by monsoonal rains during the wet season and parched to tinder dryness during the long dry — supports an extraordinary assemblage of wildlife, including the world's most diverse lizard communities, remarkable endemic marsupials, the world's largest crocodilian (the saltwater crocodile), and millions of waterbirds that congregate on the seasonal wetlands of Kakadu and other iconic parks.

Fire Management

Indigenous Australians have managed the savanna with fire for at least 50,000 years — using carefully timed, patchy burning to maintain the mosaic of habitat ages that maximises biodiversity and reduces the risk of catastrophic late dry-season fires. After European settlement, traditional fire management was largely abandoned across most of northern Australia, leading to the accumulation of large fuel loads and a shift toward the intense, late dry-season fires that are ecologically damaging. A revival of traditional "cool fire" management — facilitated through partnerships between indigenous land managers and conservation agencies — has been one of the most significant conservation successes in recent Australian history.

The Mammal Decline Crisis

Australian savannas are experiencing a catastrophic decline in small and medium-sized mammal populations — one of the most severe mammal extinction events occurring anywhere in the world. Species that were abundant across the savanna landscape as recently as the 1970s have collapsed or disappeared across large areas. The primary driver is predation by feral cats — now present at densities far exceeding those of any native predator — which have proven devastating to the native mammal fauna, which evolved without exposure to efficient felid predators. Invasive grasses (particularly gamba grass) that produce fuel loads several times greater than native grasses, generating fires of unprecedented intensity, are also implicated in mammal decline across large areas.

Australian Savanna — Fire, Invasives, and Mammal Collapse

The tropical savannas of northern Australia — covering approximately 2 million square kilometres of the Northern Territory, Queensland, and Western Australia — support the most species-rich fire-dependent ecosystem in the southern hemisphere but are experiencing one of the worst mammal extinction crises on Earth. Since European colonisation and the introduction of domestic livestock, cats, foxes, and exotic pasture grasses, approximately 30 mammal species have gone extinct or suffered catastrophic population collapses across northern Australia. The causes are multiple and interacting: feral cats — Australia's most devastating invasive predator, killing an estimated 1.4 billion native animals annually — have proven devastating to the ground-dwelling marsupials, native rodents, and reptiles that characterise savanna fauna. Invasive grasses, particularly gamba grass (Andropogon gayanus) introduced from Africa for pasture improvement, produce fire intensities 10 times greater than native grass, killing the tree communities that provide nesting sites for hollow-dependent species and foraging resources for insectivorous bats and birds.

Australia's Tropical Savannas — A Continent Apart

Australian tropical savannas — covering approximately 1.9 million square kilometres across northern Australia — are structurally and ecologically distinct from their African counterparts, shaped by a different evolutionary history, different fauna, and a fire regime of extraordinary intensity. Australian savannas are dominated by spinifex grasses (Triodia species) and Eucalyptus woodlands, with a mammal fauna that until European colonisation was dominated by marsupials — kangaroos, wallabies, wombats, and their relatives — rather than the placental ungulates of Africa. The introduction of cattle, water buffalo, pigs, feral horses, and feral donkeys since the 18th century has fundamentally altered Australian savanna ecosystems, changing fire regimes, degrading waterholes, and competing with native fauna for food and water.

Australia has experienced the world's worst rate of mammal extinctions since European colonisation — approximately 30 endemic mammal species have gone extinct, and another 50+ are threatened. Northern Australia's savannas have been particularly hard hit: monitoring programmes have documented dramatic declines in small and medium-sized mammals (particularly those in the 35-5,500 gram "critical weight range") over the past 30 years in areas with apparently intact habitat. The primary driver appears to be predation by feral cats and invasive black rats, combined with changes in fire management that have reduced the structural heterogeneity of vegetation that provides refuge from predation. The loss of these small mammals has cascading effects on seed dispersal, insect regulation, and soil bioturbation that alter the entire savanna community.

Indigenous Fire Management — Ancient Wisdom, Modern Conservation

Aboriginal Australians have managed northern Australia's savanna landscapes through carefully timed patch burning for at least 50,000 years — a practice that created the fine-grained mosaic of different fire ages that maximised biodiversity and resource availability. The abandonment of traditional burning following colonisation allowed fuel loads to accumulate, resulting in catastrophic late dry-season wildfires that burn large areas at high intensity rather than the cool early dry-season patches of traditional management. The return of Indigenous ranger programmes and traditional burning across northern Australia — formally recognised in carbon credit schemes that pay communities for emissions reductions from improved fire management — is demonstrating measurable benefits for biodiversity, carbon sequestration, and Indigenous cultural continuity simultaneously.

Australia's Tropical Savannas — Fire and Biodiversity

The tropical savannas of northern Australia — a vast belt of fire-maintained grassland and open woodland stretching across the Northern Territory, Queensland, and Western Australia — represent one of the most extensive intact savanna systems remaining on Earth, covering approximately 1.9 million square kilometres. Unlike African savannas, Australian tropical savannas evolved without large browsing mammals and without large felid predators: the megafaunal extinctions that followed human arrival 50,000-60,000 ago removed the marsupial megafauna — diprotodons, giant kangaroos, and large carnivorous marsupials — leaving a fauna dominated by medium-sized kangaroos and wallabies, monitor lizards, snakes, birds, and an extraordinary diversity of invertebrates. The Aboriginal peoples who managed these landscapes for 50,000+ years used fire as the primary tool for maintaining the mosaic of open grassland and woodland that supports game, fruit-bearing plants, and edible invertebrates.

The invasion of Australian savannas by exotic grasses — particularly buffel grass (Cenchrus ciliaris) from Africa and gamba grass (Andropogon gayanus) from West Africa, introduced as pastoral pasture improvements — represents one of the most serious biosecurity threats to Australian biodiversity. These African grasses produce dramatically more fuel than native species, generating fires of two to five times the intensity of natural Australian savanna fires. Such intense fires kill mature trees that would survive lower-intensity burns, converting biodiverse native savanna woodland to near-monocultures of the exotic grass, which recovers rapidly after fire while native species do not. The feedback loop between high fuel loads, intense fires, tree mortality, and increasing grass dominance constitutes what ecologists call a grass-fire cycle — a positive feedback that can convert diverse native savanna to degraded pasture within decades of exotic grass establishment.