From apricot-coloured cowries to truffle-eating potoroos, acclaimed conservationist and scientist Tim Flannery explores an area of biodiversity in south-western Australia as unique as the Amazon.
Mention biodiversity hot spots and most of us think of the Amazon or Africa’s Masai Mara. Yet biodiversity is not just about rainforests and rhinos. Over the past decade or so, scientific research has established that Australia’s south-west corner is home to a unique concentration of biodiversity hot spots. Spectacular flowers, parasitic trees, disappearing tortoises and unique marsupials form just part of a biological richness that is second to none.
Australia’s south-west is mostly flat, sandy and covered in heath-like vegetation known as kwongan. With wet winters and dry summers, for much of the year the waist-high scrub can look barren. But in spring its diversity is revealed in the form of thousands of plant species found nowhere else – from kangaroo paw to ground orchids and native daisies – all put on a brilliant display drawing visitors from around the world. The reason why this flat, infertile landscape supports a biological richness rivalling rainforests has long been a mystery. The answer, it turns out, lies in the very infertility of the soils and the harsh climate. Where soils are richer and annual rainfall is more uniform, the few plant species that can best utilise nutrients and water are the ones that tend to dominate. On the infertile kwongan, however, subtle differences in water and nutrient availability – caused by sand-ridges, hollows and clayey areas – allow highly specialised types to take advantage of particular circumstances. Take 10 paces through the kwongan and you may well have passed through the habitats of a hundred such species.
But why all the flowers? Again, the infertility of the soils may be the cause. There are not enough nutrients to support many pollinators and, in a sort of war of the roses, the plants have evolved to compete for them by growing very showy flowers. One pollinator that manages to survive in the kwongan, despite the harsh conditions, is the honey possum. Not much bigger than your thumb, these diminutive, striped and long-snouted creatures are distant relatives of kangaroos. But it’s the way they approach reproduction that sets them apart. Male honey possums have the largest sperm of any mammal – longer even than those of the blue whale, and their testes are so large that the males can sit on them, rather like a portable chair. Just why the male honey possum is so formed remains a deep biological mystery.
One of south-western Australia’s oddest plants does not flower in spring with the rest, but at the height of summer. Known as the Western Australian Christmas tree, its brilliant orange blooms are one of the first things a visitor sees when landing at Perth airport. A tree-sized member of the mistletoe family, the Christmas tree parasitises grasses by piercing their roots with a tiny and unique spigot-like structure. It can afford to flower in the heat of summer – and so avoid the springtime competition for pollinators – because it steals water and nutrients from its victims.
Not all of the vegetation of the south-west is scrubby. The Pemberton and Denmark regions south of Perth shelter some of the tallest flowering plants on Earth. The karri is a kind of eucalypt that reaches a height of 80m. When I was 19, I drove my motorbike from Melbourne to Pemberton to see the karri forest. I’d heard about one special forest giant called the Gloucester Tree. In 1946, a series of stakes had been driven into the 61m high tree so that it could be climbed and used as a fire lookout. It can still be climbed by visitors. On the day I scaled it there was a stiff wind blowing and I felt a bit like a storm-tossed sailor headed for the crow’s nest.
When I reached the top, I discovered that the tree was swaying several feet, but the view over the surrounding forest was sublime.
One of the most astonishing things about Australia’s south-west is the abundance of living fossils that survive there, an encounter with any of which offers the chance to peer back in time. Just why the region harbours so many antique relics is not clear, but its isolation and an unusually stable long-term climate may be significant factors. The western swamp tortoise is one such wonder. As Australia’s smallest tortoise, it’s a relic of a group that, more than 15 million years ago, was once widespread in Australia. The first specimen came to light in 1839, soon after Perth was founded, but it was not seen again for more than a century. It was assumed to be long-extinct until, in 1954, a schoolboy showed one in a suburban pet show and a scientist happened to see it. The creature had been rediscovered in the nick of time, for without active protection and a breeding program run by Perth Zoo, urban expansion and introduced predators would have exterminated it long ago. Today just 400 individuals survive, making it the most endangered freshwater tortoise on Earth; its total habitat comprising two swamps on the northern outskirts of Perth (at Ellen Brook and Twin Swamps nature reserves). Even there it’s hard to see, as it spends eight months every year hibernating in the soil, emerging only after good winter rains.
Other ancient inhabitants are more visible. Visitors to Rottnest Island cannot help but become acquainted with the quokka, a tiny member of the kangaroo family that was once abundant throughout the south-west, but which now survives only on islands and in a few protected places on the mainland. Its dentition is similar to that of Queensland’s tree kangaroos and it may be a distant relative of the group, which was stranded in the south-west by a changing climate – or perhaps these similarities evolved independently. In the 19th century, quokkas kept company with an even tinier member of the kangaroo family. Known as Gilbert’s potoroo, it is an eater of truffles and other fungi. It vanished around 1870 and was not heard from again until a tiny population was rediscovered in 1994 at Two Peoples Bay, near Albany. Despite intensive efforts to get them to breed, only 40 or so survive, making it one of the most endangered mammals on Earth. Recently, a few were released on an offshore island, where they seem to be slowly increasing in number.
One of the best places to see the south-west’s unique marsupials is at Karakamia Sanctuary. Located some 50km north-east of Perth, it’s run by the Australian Wildlife Conservancy (AWC). About 3sq km of native forest has been fenced off from introduced predators, allowing bandicoots, rat-kangaroos, quokkas and numbats to abound. I’m a long-time supporter of the AWC, so I feel a special pride in seeing how my donations are working to preserve Australia’s natural heritage. A night walk through the sanctuary is immensely exciting. In the guide’s spotlight, you are able to see some of Australia’s rarest creatures in action and learn how their digging and scratching transforms the soil and changes the vegetation.
South-west Australia’s amazing biodiversity is not restricted to the land, for its waters, too, are home to species found nowhere else. Look in the shallow pools and streams and you might see the salamander fish. Just a few centimetres long, this unassuming creature was discovered only in 1961. Able to breathe air and survive for months in the mud if its pool dries up, it may be a relative of the pike family that has been isolated in the south-west for more than 100 million years.
Cowrie shells bring to mind brilliant tropical reefs, but some of the most beautiful cowries on Earth are found only in the south-west. Again, many are a kind of living fossil, which for some reason died out elsewhere long ago. Perhaps the most beautiful is the apricot cowrie. Its shimmering, orange-pink coloured shell can grow to the size of a small apple and is much sought-after by collectors. It lives on sponges at depths of 100m or more, where it is occasionally trawled from the dark and frigid depths by fishing boats. The apricot cowrie lays just a few eggs, which the mother carefully looks after and which hatch as tiny crawling snails.
Biodiversity hot spots are, by their very definition, under threat. Quite apart from giving them a sort of last-chance-to-see attraction, they are often the focus of heroic biodiversity conservation programs, and nowhere is this more true than in Australia’s south-west. Organisations such as the Australian Wildlife Conservancy offer the chance for members of the public to become involved in such work, which means that you can become much more than a tourist marvelling at threatened wonders.
Source Qantas The Australian Way February 2011