Rising abruptly from the flat plains, the Stirling Range, Koi Kyeunu-ruff to the Noongar people, draws clouds, rain and people’s eyes to its dramatic peaks and ridges.
The Stirling Range itself stretches about 65km (about 40 miles) from west to east and is about 40km (25 miles) inland from the Southern Ocean. Once, the rocks that comprise the Range were beneath the ocean, laid down as sands and silts in the delta of an ancient and long forgotten river more than a billion years ago. Pressure from the weight of the sediments themselves and from the movements and faulting between Australia and Antarctica produced metamorphic sandstones, quartzites and shales that were folded and formed a mountain chain that rose high above the surrounding granite surface about 65 million years ago. Over time, that mountain chain and the surrounding plains have been worn down by aeons of rainfall and chemical weathering. Today the Range forms a chain with two distinct parts: an eastern ridge contains the highest peak, Bluff Knoll or Bular Mial at 1095m, and a series of other lower ridge summits; and the western chain of separated peaks, including the second highest, Mt Toolbrunup at 1052m. The Chester Pass Road runs between the two portions.
Bular Mial means “many eyes” and refers to the impression given by the exposed rocks and features of the Knoll that resemble watching eyes.
The Range is high enough to have a distinct impression on the region’s climate. To the south, rainfall is around 600mm or more and much of the land beyond the immediate surrounds of the range is cropped, grazed on introduced pastures, or under plantation forests. To the north, rainfalls fall off to 400mm or less and the wheatbelt begins. On the peaks themselves, rainfall can be as high as 1100mm annually and on the highest peak, snow can occasionally fall – the only place in Western Australia where that occurs semi-regularly - although it is usually short lived. One of the most dramatic features of the Range is the cloud formations that can envelop the peaks completely, form swirling mists around them, or on occasion form a soft sheet that appears to glide across and over the Range, wrapping it in soft layers. For the Noongar people, the mists are tangible evidence of the Noyt or spirits of their people who have passed away.
Fortunately, the Range itself and some of the surrounds were reserved as National Park in 1913 and some further areas of heathlands surrounding the Park escaped development for agriculture, probably because of the presence of concentrations of poison plants, native plants mostly of the Gastrolobium genus that have naturally high levels of fluoroacetates that are toxic to non-native animals. The Stirling Range National Park now covers about 1,159km2 (about 450 square miles) and is managed by the Western Australian Department of Environment and Conservation.
Not surprisingly, the combination of a different geology and the moisture-drawing heights have contributed to a wealth of botanical treasures even by southwest Australian standards. More than 1500 taxa of plants are known from the National Park and at least 87 of these are endemic to the Park. As well as the thickets, woodlands and mallee-heaths, there are areas of wetlands and salt lake communities to the south east and north east of the Park that add to its richness. The cool moist gullies are also home to a number of Gondwanan relict fauna, including the Stirling Range Moggridgeae and species of Neohomogona, another trapdoor spider. Other invertebrates that have found refuge in moist shaded upland sites in the Range include species of land snails, including Bothriembryon species and species from the Paryphanitidaae and Rhytididae families, and a giant earthworm (Megascolex sp).
About 140 bird species have been recorded for the Park, including the Western Whipbird Western Whipbird (Psophodes nigrogularis oberon), Mallee Fowl (Leipoa ocellata), Carnaby’s Cockatoo (Calyptorhynchus latirostris) and Baudin’s Cockatoo (Calyptorhynchus baudinii). Around 30 reptile species occur there as well as 20 other vertebrate animals. Like much of the southwest, this is a reduced suite of species however, with fauna such as the Bilby, Burrowing Bettong, Chuditch, Crescent Nailtail Wallaby, Red-tailed Phascogale, Western Barred Bandicoot and Western Ringtail Possum believed to have once occurred there but not found there now. Other species such as the Numbat are being reintroduced as part of species recovery programs in combination with intensive predator (red fox, cat) controls.
Invertebrate fauna are not as well known, although the small brown azure butterfly (Ogyris otames), is known from an area of wandoo woodland where Armillaria fungus was observed in the early 1990s to be killing broom bush (Choretrum glomeratum), the butterfly larvae’s only food plant of the butterfly larvae.
Many of the special flora, including species like the Mountain Bells (Darwinia species) and Banksia brownie are highly susceptible to Phytophthora cinnamomi, a soil-borne fungus that causes dieback and death of many of the proteaceous plants in particular. Phytophthora is widespread in the Park, believed to have been introduced and spread as early as the 1940s in road building material, and has been further spread by additional road construction in the 1970s, vehicle movements, on walkers’ boots and possibly even by native animals. The thicket and heath communities of the eastern Stirling Range peaks are now listed as a Threatened Ecological Community – considered Critically Endangered under Western Australian legislation and as Endangered under the national Environmental Protection and Biodiversity Act. This is primarily due to their susceptibility to dieback, but also to their sensitivity to fire and vulnerability to other disturbances such as rabbits. Ten of the individual flora species that make up these communities are also listed under the EPBC Act.
While the highest peaks can receive light rain or moist mists year round, this doesn’t mean that the Range escapes the summer heat, and fire is a constant danger to the survival of some of the more sensitive communities. The combination of too frequent or too intense fire and Phytophthora can be catastrophic.
The Stirling Range National Park is only about 22km north of the Porongurup National Park and a local community group has secured a private reserve, Twin Creeks Reserve, and commenced the Ranges Link program to build connectivity between the two parks. Bush Heritage Australia and Greening Australia have jointly purchased Yarrabee, a former farm adjoining the eastern end of the Stirling Range National Park, to protect its remaining heathland communities and anchor the western end of the Fitz-Stirling link.
And just as well. Recent research have identified the concentrations of plant species richness across the south west. Surprisingly, it is not just the Stirling Ranges that rank highly, but the Kalgan Valley and sandplains surrounding the park to the west, south and east. That is where Gondwana link groups have concentrated their efforts, for now at least.