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Rewilding Australia

With the decline in Tasmanian devil numbers due to disease, carcasses now persist more than twice as long in Tasmanian landscapes. Credit: Rafael Ben-Ari/Adobe

With the decline in Tasmanian devil numbers due to disease, carcasses now persist more than twice as long in Tasmanian landscapes. Credit: Rafael Ben-Ari/Adobe

By Chris Johnson

Sometimes the best way to conserve biodiversity is to stand back and let wild animals do the hard work of ecological management.

In December 2012, the Copenhagen Post reported a discovery that marked a historic turning point for nature in Denmark: the first confirmed record of a wolf in the country in 200 years. Since then, more wolves have been found in the same area, suggesting the existence of a resident pack. One of the most developed countries in Europe just got a bit wilder.

This was not an isolated event. Across Europe, big carnivores are coming back, including wolves, bears, lynx and wolverines.They are mostly managing this by natural population increase and long-distance migration. For instance, DNA analysis showed that some of the Danish wolves had travelled 700 km from eastern Germany. Sometimes conservation organisations have assisted this migration. Brown bears, for example, have been reintroduced to the Italian alps, where they are doing well.

At the same time, large wild herbivores are being restored to some European landscapes. These animals include European bison and even breeds of cattle selected to resemble the aurochs, a massive beast that was the ancestor of domestic cattle and went extinct in the 17th century. Another big turnaround has been in the population of the Eurasian beaver, which was hunted almost to extinction by the end of the 19th century but is back up to 30 million.

These changes are all part of a new philosophy of nature conservation called rewilding, which aims to re-establish ecologically powerful animals like these big herbivores and predators so that they can influence ecosystem processes and sustain biodiversity.

The emphasis on very big animals is not just due to their charisma; it is a recognition of the crucial roles they play in ecosystems. Top predators like wolves keep populations of smaller predators in check, and thus protect many other animals that would be threatened if these smaller predators were freed from control. They also regulate populations of herbivores and therefore prevent overconsumption of vegetation.

Large herbivores, on the other hand, can help to maintain the diversity of plants and habitats by creating open areas in otherwise dense vegetation. Beavers are powerful “ecosystem engineers” that physically transform whole environments. In Europe, reintroduced beavers have recreated wetlands with a high diversity of plants and animals.

The problem that rewilding aims to solve is that the biggest animals have disappeared from most of the world’s ecosystems. This began about 50,000 years ago when a global wave of extinctions known as the “Pleistocene megafaunal extinction” saw the end of mammoths, ground sloths and many other giants, probably at the hands of human hunters. The few megafaunal species that survived into the modern world are now typically rare, and a large proportion are continuing to decline towards extinction.

Rewilding projects try to rebuild some of the lost structure of ecosystems by restoring megafauna. Where possible, this is done by protecting surviving species and helping them recover some of the ground they have recently lost, like those wolves and bison in Europe. It can also mean substituting different species for those that went extinct thousands of years ago, if the substitutes are similar enough to the originals that they could perform the same ecological functions. There have been serious proposals, for example, to introduce elephants to parts of Europe to make good the loss of Europe’s own elephants. We could throw in a few lions and hippos for the same reason.

Rewilding in Europe has not gone quite that far yet, but it has given us some conservation success stories that stand out as bright spots in the generally dark picture of global decline in biodiversity. Is the concept useful for Australia? Two facts suggest that it could be.

First, Australia once had its own megafauna, an amazing array of large predators like the marsupial lion and giant herbivores such as diprotodons. Their extinction could have had important repercussions for Australian ecosystems. Tim Flannery has suggested that the disappearance of diprotodons and giant kangaroos around 40,000 years ago could have promoted the incidence of bushfires due to the accumulation of dry plant material that would otherwise have been eaten by the herbivores. There is some evidence for this, and there is overwhelming evidence that where big herbivores still exist in other parts of the world they can prevent destructive fire.

Recent events have forced Australians to confront the reality that our already flammable continent is becoming even more fire-prone, with potentially devastating consequences for people and nature. Perhaps rewilding could help protect us from this.

The second fact is Australia’s recent record of extinction. We have lost more species of mammals over the past 200 years than any other country, and on the whole the status of surviving species is getting worse, not better. The main cause is predation by the red fox and feral cat. An important reason that these predators kill so much wildlife in Australia is the lack of larger native predators that dominate them. Viewed in this light, Australian environments need more predators as long as the ones that we add or put back take on the top-predator role.

The main dilemma for rewilding in Australia is that our megafaunal extinctions were so complete, and the animals that we lost so unique, that it’s very difficult to imagine how we could replace them. It would be outlandish, for example, to propose introducing the African lion as a substitute for the extinct marsupial lion.

Nonetheless, we still have some great opportunities for rewilding with predators. One of these is provided by the dingo. Where dingoes are abundant, they control and stabilise populations of kangaroos and introduced herbivores like feral goats. They also reduce populations of the red fox and possibly the feral cat. As a result, the condition of the vegetation is typically better in the presence of dingoes, and there are more native small mammals, ground-nesting birds and other species that would otherwise be killed by foxes and cats. Dingoes are heavily controlled in many parts of Australia because of the partly real, partly perceived threat they pose to livestock. Simply relaxing control of dingoes could be an effective strategy for rewilding.

Then there is the Tasmanian devil. Until a few thousand years ago it was widespread on the main island of Australia. It could easily be reintroduced to at least some conservation areas on the mainland.

Why do that? The recent decline of the devil in Tasmania due to devil tumour facial disease has given us an opportunity to study the effects it has on ecosystems. One result is that devils are able to control feral cats. They also control populations of some herbivores, like the common brushtail possum, that can become overabundant without predators. And they perform the useful function of cleaning up the carcasses of bigger animals like kangaroos. These carcasses now persist more than twice as long in Tasmanian landscapes in the absence of scavenging by devils. It is time we thought seriously about bringing the devil back home to mainland Australia.

What about the gap left in Australian ecology by the extinction of our giant herbivorous marsupials? In a sense this has already been filled. Many large herbivores were introduced to Australia from Europe and Asia during the 19th and early 20th centuries, and they are now flourishing. For example, Australia has six species of wild deer, which is more than many countries where deer are native.

The problem is that these animals are at best only very approximate replacements for our extinct mega-herbivores. To some extent Australian vegetation is well adapted to the browsing and grazing imposed by deer, water buffaloes and others, but those animals’ hard hooves do extra damage. The same is true of the way that deer stags damage vegetation by thrashing saplings with their antlers.

Perhaps the species that comes closest to substituting for extinct Australian megafauna is the one-humped camel. The camels that roam across central Australia browse on thorny vegetation that would once have been eaten by diprotodons and other marsupial mega-herbivores, and their soft feet do less harm than the hooves of other introduced herbivores. But camels still cause significant damage when their numbers are high, especially to precious desert waterholes.

None of this is to say that the large herbivores introduced to Australia have no ecological value. Probably they do, and under some conditions that could include controlling fire risk. The challenge for Australian ecologists is to discover what those benefits might be and work out how to manage the abundance of those animals so that their benefits outweigh their harms.

The other important category of animals that could help to rewild Australia is the ecosystem engineers. Australia has nothing quite like a beaver, but we have a remarkable suite of small- and medium-sized mammals that shape the physical environment by digging for their food. Rat-kangaroos (potoroos and bettongs) are the most industrious of these engineers, and bilbies and bandicoots are not far behind. By digging holes and turning over soil, these animals improve soil fertility, enhance regeneration of plants and create new habitat for invertebrates. They also mix leaf litter with soil, and this activity limits the accumulation of dry plant matter on the forest floor. This, in turn, reduces the availability of fuel for fire and therefore reduces bushfire risk.

These species have all declined dramatically, but there are remnant populations that could provide animals for re­introduction to their former ranges. Doing this could improve the health of many woodland environments and reduce the impact on them of bushfire. It would succeed only if we had some way of suppressing foxes and cats in the same landscapes, but that could possibly be done by restoring dingoes or devils at the same time.

So there is potential for rewilding to work in Australia, using species that are already here. The key will be to look at our environment, including both our native and introduced species, with fresh eyes. Where we now see problems, we need to envision solutions that could come from thinking and acting differently.

Chris Johnson is Professor of Wildlife Conservation at the University of Tasmania, and a member of the Australian Research Council Centre of Excellence for Australian Biodiversity and Heritage.