EcoCheck: Australia’s vast, majestic northern savannas need more care

By Euan Ritchie, Deakin University and Brett Murphy, Charles Darwin University

Storm season in the Australian tropical savanna. Euan Ritchie, Author provided

Australia’s Top End, Kimberley and Cape York Peninsula evoke images of vast, awe-inspiring and ancient landscapes. Whether on the hunt for a prized barramundi, admiring some of the oldest rock art in the world, or pursuing a spectacular palm cockatoo along a pristine river, hundreds of thousands of people flock to this region each year. But how are our vast northern landscapes faring environmentally, and what challenges are on the horizon?

Above 17° south, bounded by a rough line from Cairns, Queensland, to Derby, Western Australia, are the high-rainfall (more than 1,000mm a year) tropical savannas. These are the largest and most intact ecosystem of their kind on Earth. With the exception of some “smaller” pockets of rainforest (such as Queensland’s Kutini-Payamu (Iron Range) National Park), the vegetation of the region is dominated by mixed Eucalyptusforest and woodland with a grassy understorey.

Within the fire-prone Great Northern Savannas exist fire-sensitive communities such as these Allosyncapria ternata rainforests along the edge of the Arnhem Plateau in Kakadu National Park. – Image Credit: Brett Murphy

There is a distinct monsoonal pattern of rainfall. Almost all of it falls during the wet season (December-March), followed by an extended dry (April-November). Wet-season rains drive abundant grass growth, which subsequently dries and fuels regular bushfires – making these landscapes among the most fire-prone on Earth. The dominant land tenures of the region are Indigenous, cattle grazing and conservation.

These savannas are home to a vast array of plant and animal species. The Kimberley supports at least 2,000 native plant species, while the Cape York Peninsula has some 3,000. More than 400 bird and 100 mammal species call the region home, along with invertebrates such as moths, butterflies, ants and termites, and spiders. Many of the latter are still undescribed and poorly studied.

Many species, such as the scaly-tailed possum, are endemic to the region, meaning they are found nowhere else.

A large male antilopine wallaroo, endemic to tropical Australia. – Image Credit: Euan Ritchie

The general lack of extensive habitat loss and modification, as compared to the broad-scale land clearing in southern Australia since European arrival, can give a false impression that the tropical savannas and their species are in good health. But research suggests otherwise, and considerable threats exist.

Fire-promoting weeds such as gamba grass, widely sown until very recently as fodder for cattle, are transforming habitats from diverse woodlands to burnt-out, low-diversity grasslands. Indeed, the fires themselves, which are considered too frequent and too late in the dry season at some locations, are now thought to be a primary driver of species loss.

Notable examples of wildlife in trouble include declines of many seed-eating birds, such as the spectacular Gouldian finch, and the catastrophic decline of native mammal species, most prominently in Australia’s largest national park, Kakadu.

Added pressures include bauxite miningforestry and cattle grazing. The latter activity exerts strong pressures on the characteristically leached, nutrient-poor, tropical soils. Most recently, changes to Queensland’s land-clearing laws have led to virgin savanna woodland being cleared.

It is likely some threats may also combine to make matters worse for certain species. For instance, frequent fires, intensive cattle grazing and the overabundance of introduced species such as feral donkeys and horses all combine to remove vegetation cover. This, together with the presence of feral cats, makes some native animals more vulnerable to predation.

New threats

This globally significant ecosystem, already under threat, is facing new challenges too. Proposals to use the region as a food bowl for Asia are associated with calls for the damming of waterways and land clearing for agriculture.

This is against a backdrop of climate change, which among other effects may bring less predictable wet seasons, more frequent and intense storms (cyclones) and fires, and hotter, longer dry seasons. Such changes are not only likely to harm some species, but could also make those much-touted agricultural goals far more difficult to achieve.

Added pressures include bauxite miningforestry and cattle grazing. The latter activity exerts strong pressures on the characteristically leached, nutrient-poor, tropical soils. Most recently, changes to Queensland’s land-clearing laws have led to virgin savanna woodland being cleared.

It is likely some threats may also combine to make matters worse for certain species. For instance, frequent fires, intensive cattle grazing and the overabundance of introduced species such as feral donkeys and horses all combine to remove vegetation cover. This, together with the presence of feral cats, makes some native animals more vulnerable to predation.

New threats

This globally significant ecosystem, already under threat, is facing new challenges too. Proposals to use the region as a food bowl for Asia are associated with calls for the damming of waterways and land clearing for agriculture.

This is against a backdrop of climate change, which among other effects may bring less predictable wet seasons, more frequent and intense storms (cyclones) and fires, and hotter, longer dry seasons. Such changes are not only likely to harm some species, but could also make those much-touted agricultural goals far more difficult to achieve.

If you are a researcher who studies an iconic Astralian ecosystem and would like to give it an EcoCheck? You can get in touch via: mailto:michael.hopkin@theconversation.edu.au

Source: The Conversation