When it comes to the environment, it's easy to feel like we're on a perpetually downward spiral. Species go extinct, habitats get knocked down, and rivers get dammed and drained.

Key points: Around 20 species will be reintroduced to the peninsula

Around 20 species will be reintroduced to the peninsula A 17-kilometre fence will stretch across narrow point

A 17-kilometre fence will stretch across narrow point Species include bilbies, numbats, and quolls

But an ambitious new rewilding project on the Yorke Peninsula in South Australia will attempt to restore a small pocket of Australia to its former ecological glory.

In total, about 27 of 29 mammal species are believed to have disappeared from the peninsula, including keystone species which help shape the ecosystem, according to the Head of Living Ecosystems from WWF, Darren Grover.

"Over the last 150 years or so, there's been pretty extensive agriculture … and Innes National Park was a mine back in the day," he said.

"If nothing was done about it, those local ecosystems and the landscape as a whole would continue to deteriorate over time."

Although some of those 27 species have gone extinct, about 20 including bilbies, quolls and numbats, will be reintroduced to the site from other habitats around Australia.

The rewilding project, which officially launches today after 10 years of planning, will begin by building a fence across the narrowest section of the peninsula to help control foxes and feral cats entering the 120,000-hectare sanctuary.

Over the next few years, in a collaboration between partners including Naturally Yorke, the South Australian and federal governments, WWF and Greening Australia, breeding populations of numerous threatened species will be reintroduced to the sanctuary — dubbed the "great southern ark".

At the same time, pest-control programs will be conducted to ensure the best chance of survival for the animals, according to Mr Grover.

"I don't think we can understate that these are bold, risky projects, but we're facing a species-extinction crisis in Australia," he said.

"We can't keep going along doing what we've been doing because it's not working. We need to take some risks."

Pioneering woylie first to be reintroduced

Bettongs are ecosystem engineers that help other species establish. ( Supplied: Zoos Australia )

The tender for the fencing contract closes today, and Mr Grover hopes construction will begin in the next few weeks.

The first species to be reintroduced will be a population of woylie — or brush-tailed bettong — which are known as an "ecosystem engineer" species.

Woylies excavate tonnes of soil each year in search of food, and in doing so, help propagate native plant seedlings. This then enhances the habitat for other species that rely on native plants, and so on.

Red-tailed phascogales — small carnivorous marsupials — will also be introduced early on, as will bandicoots. A fledgling owl population will be supported with nest boxes.

Some species depend on the activity of others in order to survive in the ecosystem, so it's hoped strategically staggering the reintroduction of these species can help restore that function, according to Jasmine Swales.

Bilbies are one of the animals slated for reintroduction to the Yorke Peninsula. ( Supplied: SA Environment Department )

"The soil engineers are crucial to restoration. They spread mycorrhizae [symbiotic fungi] by foraging under the native vegetation … and have a much greater biological role to play than rabbits and other non-native species," Ms Swales, a ranger with Natural Resources Northern and Yorke, said.

"Each reintroduction will be reliant on the success of the last."

And it's this whole-of-ecosystem strategy that has garnered the approval of Rewilding Australia, according to the group's director, Rob Brewster.

"I think it's really good. It's an ecosystem-focused approach and … it's really looking at a long-term strategy," he said.

The ability to fence off the sanctuary is a significant advantage to rewilding in an Australian context, according to Mr Brewster.

"One of the big problems in Australia is that our key threats to a lot of these mammals are still operating in the environment. Foxes and feral cats are operating 24 hours a day," he said.

"A fence is good for the 1 per cent of Australia that you can actually put a fence around."

But rewilding parts of mainland Australia that can't be fenced is a different challenge altogether, according to Mr Brewster, who highlighted the need to look at lateral solutions to the problem of pests.

Tasmanian devils solution to cat problems on mainland?

Tasmanian devils could be reintroduced to the mainland to help limit feral cat predation. ( Supplied: Mark Marathon )

A source of inspiration for the Yorke Peninsula project, and many other rewilding projects around the world, comes from Yellowstone National Park in the US.

A small population of wolves were reintroduced to that region, which preyed on out-of-control deer, setting off a trophic cascade which produced increased forest cover, more birds of prey and the return of beavers to the rivers.

Tasmanian devils went extinct on the mainland about 3,200 years ago. ( Department of Environment )

In Australia, the rewilding movement is steadily gaining momentum with groups like Rewilding Australia advocating for the reintroduction of Tasmanian devils to the mainland.

Tasmanian devils disappeared from the mainland along with Tasmanian tigers around 3,200 years ago.

But research suggests introducing devils to the mainland could help knock cats and foxes off the top-predator pedestal in places where dingoes are culled or are in low numbers.

Re-establishing ecosystem structures could be the key to curbing Australia's alarming extinction rate, according to Mr Brewster.

"Australia has been isolated for 40 millions years and we've got a complex web of relationships between species," he said.

"If we lose those species, those links break down. One species going extinct can cause a whole suite of others to go as well."

If the "great southern ark" proves successful, proponents like WWF's Darren Grover hope rewilding can help to restore some of Australia's degraded ecosystems.

"We hope to use the peninsula as a model for other parts of the country where animal species have faced mass extinction," he said.