Australia: The Land Where Time Began

A biography of the Australian continent 

Southwest Tasmania

The rocks of the area were deposited as sediments some time before 700 Ma, the subsequent metamorphosis converting them into quartzites and schists. Later folding buckled the rocks into mountain ranges that were much higher than those that remain, erosion having worked on them for millions of years, removing much of the softer schists and other softer rocks, leaving the resistant quartzites as jagged ridges of vertical strata. The result of the erosion was a series of craggy ranges separated by wide valleys. Later glaciation has enhanced the contrast, the cragginess of the ridges and the softer, roundness of the valleys.

Federation Peak

Examples of this type of scenery is found in the Western Arthur Range, Sentinel Range and Frankland Range. Rocks of many colours are often exposed near the summits of the ranges. At 1233 m high at the southeastern end of Arthur RangeFederation Peak is one of the most spectacular landforms in the southwest. The pinnacle is more than 600 m high, is composed of whitish-grey quartzite. Several similar, but blunt topped peaks flanking the main peak, each peak being separated from its neighbours by deep gaps with sheer sides. The peaks are all on the rim a very large cirque (a basin-shaped hollow gouged out by a glacier). Lake Geeves lies in the valley in the centre of the cirque facing to the southwest.

A few hundred metres to the southwest of Federation Peak, but separated by a huge chasm, is small Hanging Lake, at an elevation of 1000 m.

The area known as the southwest covers an area of about 13,000 km2 in the southwest of Tasmania. The highly resistant, ancient rocks have formed distinctive landforms that are believed to have remained practically unchanged since the glaciers melted between about 12,000 and 6,000 BP. As with Tasmania as a whole, it lies within the belt of the Roaring Forties, a wind that blows unimpeded by land across the Southern Ocean to bring rough seas and a cool rainy climate to the island. The weather in the region is similar throughout the year, with frequent powerful storms  and often torrential downpours, hail, sleet and snow. The only time of the year when there  is some relief is in January and February.

This is one of the few places in the world where the natural balance hasn't been disturbed by humans, and where the geology, vegetation and climate conspire to make it difficult for humans and introduced species to penetrate the area. The Aboriginal occupation of the area, which lasted from about 35,000 BP until white settlement, never spread more than a few hundred metres along the coastal edges.

The wild, remote region has a wide range of spectacular landforms, with a series of jagged mountain chains and extraordinary vegetation of dense tangled forests. There are small glacial lakes with quartzite peaks above, and fast flowing rivers that have cut deep gorges on the slops, that lack foothills, where there are many rapids and waterfalls. The lack of foothills results in places where the mountain ridges abruptly change to alpine moorlands and plains of buttongrass. Along the coast there are not many beaches or inlets, the sheer cliffs being directly pounded by the sea.

The Tasmanian southwest was one of the few parts of Australia that had glaciers during the Pleistocene ice age.

Frenchman's Cap

One of the spectacular features of the Tasmanian southwest is Frenchman's Cap, the peak 600 m above the range, rising to 1433 m. This peak, one side of which is sheer, has the top 400 m composed of pure white quartzite. The area of the peak has been shaped by glaciation, it is ringed by cirques and tarns (lakes surrounded by mountains). The Franklin River and its tributaries almost completely surround the mountain massif.

In the central and western portions of the area quartzite peaks are the predominant feature of the landscape. In the east, however, the rocks are of a different type, more similar to those of eastern Tasmania, being ancient sandstones and limestones with a dolerite capping of a similar age and origin to that of the Tasman Peninsula and the rest of Tasmania. These folded sedimentary rocks capped by dolerite are seen in places such as the Hartz Mountains.

Mt Anne massif

An example of the scenery of the area where sedimentary rocks are caped with dolerite is the Mt Anne massif. It is a dolerite region in the midst of quartzite regions. It forms a series of jagged peaks to the east of Lake Pedder. Mt Anne is the highest of these peaks, its pyramidal summit rising to 1425 m. It is separated from the adjacent peaks of Mt Eliza and Mt Lot by wide glacial passes. The higher peaks such as these are often snow-capped or shrouded in cloud, which contrasts strongly with the dark dolerite rocks. Lakes are present in the large cirques that were formed by glaciers, the largest of which is Lake Judd, on the southern side of Mt Eliza, beneath cliffs reaching up to 300 m. The rocks underlying the dolerite of this massif are to a large extent dolomite, which is a type of limestone that is very soluble. This solubility has allowed the dolomite to be tunnelled out by seeping water to form very deep caves. Many of the shafts are snow-filled for most of the year, making it difficult to explore the known ones and leaving the possibility of many unknown caves. It it though possibly that the area may contain Australia's deepest cave that is yet to be discovered. The Hastings Caves occur in a dolomite belt to the southeast of the Mt Anne massif.

At times of low sea level during glacial periods there were coastal plains extending from 20 to 50 km  from the rugged mountains. Since the sea rose this coastal plain has been completely submerged, the only land remaining seaward of the mountains is in the form of a number of islands that are the tops of peaks on the former coastal plains. An example of these peaks that became islands is the Maatsuyker Group. Macquarie Harbour and Port Davey are 2 of the few inlets that have bays and points, but their edges mostly rise abruptly from the sea. In many places the dense forest grows up to the water's edge.

One of the best views of the area is east of Port Davey, between the 2 low promontories South East Cape (the most southerly point of Australia) and South West Cape (a granite intrusion), where a number of bays are found, such as New Harbour, Cox Bight, Louisa Bay and Surprise Bay. There are also a few white beaches, the longest in the area being the 6-5 km long Prion Beach. Dunes have formed inland of Prion Beach, beyond which is the New River Lagoon. On the shore of the lagoon is 1120 m high Precipitous Bluff and to the east is the 1250 m high Pindars Peak. Precipitous Bluff is heavily forested but above the forests rises as sheer cliffs of dolerite for 300 m above the treeline.

Vegetation

The vegetation of the South-West is unique in Australia, requiring species that can tolerate the thin, impoverished soils, the strong cold winds of the Roaring Forties and torrential rain, as well as periods of snow, hail and sleet. Only hardy plants have a chance in this tough environment. The plant cover is mostly temperate rainforests and peat-forming heaths and sedges. A factor that makes the area different from other alpine regions if the lack of a treeline, many of the trees adapt to the local conditions, stunting progressively with height and exposure to the environmental conditions. There are some areas of alpine herblands and eucalypt forests. Several of these hardy plants are endemic to the region, others being endemic to the area as wel as adjacent areas of Tasmania. Some of the plants have affinities to living and fossil plants found in the former Gondwanan continents, such as South America and New Zealand.

A number of factors interact to produce a complex distribution of the plant species comprising the various communities found in the Tasmanian Southwest, soil altitude, drainage, species, aspect (north or south-facing sides of hills) and the frequency and severity of bushfires. The area has an annual rainfall of more than 3,000 mm/year, so fire is not normally thought of as a problem. In some areas, such as the buttongrass areas, the buttongrass can burn soon after fires and as with eucalypts anywhere, their leaves contain volatile oil that promotes any fires that start.

A difference between eucalypts and rainforest trees that can determine which dominates an area subjected to fire is that eucalypts require sunlight to regenerate, whereas rainforest trees require shade and moisture to regenerate. After a fire the eucalypts regenerate, but when they reach a high enough area of ground cover they provide sufficient shade for the rainforest trees to regenerate. If the fires occur too frequently the eucalypts continue to proliferate while the regeneration of rainforest trees is reduced making it hard for them to compete. If fires are several hundred years apart the eucalypts eventually die out in the area affected. Occasional bushfires are the only reason there are any eucalypts growing in the South-West. Without bushfires the Southwest would be exclusively vegetated by rainforest species with alpine moorlands and sedgelands where the soil was too waterlogged to support trees or shrubs.

Rainforests form the most significant vegetation communities below about 1000 m elevation, with about 1/3 of the area covered by heathlands and sedgelands, as well as fairly large areas of eucalypts and flowering herblands.

The Tasmanian "myrtle" (aka Antarctic beech) (Nothofagus cunninghamii) is the most common tree of the rainforests. This species has a thick, rough, black bark and dense dark green leaves, and grows to about 30 m. The other tree species that grow amongst these trees, such as fragrant sassafras (Atherospermum moschatum) and a number of endemic conifers, depends on the soil conditions of a particular area. There is an understorey of ferns, mosses and liverworts, as well other small plants.

One of the conifers of the area is the Huon pine (Dacrydium franklinii), now rare, usually less than 35 m tall, grows on the swampy or moist soils of river flats. They have been dated by their tree rings to be as much as 2,000-3,000 years old, taking several centuries to mature. The grey bark is slightly rough, and the foliage is dark green and spindly, and it produces very small fruiting cones. Other pines of the area are the King Bill or King William pine (Athrotaxis selaginoides), growing to 30-40 m on infertile soils, and the celery-top pine (Phyllocladus aspleniifolius), growing to 20-25 m, usually on acidic soils.

It is on the acidic soils that the horizontal scrub grows. The tree (Anodopetalum biglandulosum), grows as a slender stem to about 5-10 m then bends to a horizontal position, sending out branches that also bend to grow horizontally. The result is a very dense tangle of intertwined branches and stems that can be as much as 30 m high.

The Southwest is also known for its windy tawny buttongrass plains (Gymnoschoenus sphaerocephalus), that is the main cause of the tea coloured water of the rivers and lakes of the area. There is a round on the ends of the stalks of this large bog-rush. This is the dominant plant of the heathlands and sedgelands throughout the wilderness. In areas of poor drainage it grows in tall tussocks with muddy depressions between them.  On better drained soil it grows as small mounds that make for a relatively even surface. The tea-tree (Melaleuca squarosa) is the most common of the other plants growing on the buttongrass plains. The silver Banksia (Banksia marginata), with pale yellow flowers, is also common on the plains. A plant growing along the margins of the buttongrass plains and long streams, that is almost as notorious as the horizontal scrub is the vine-like bauera (Bauera rubiodes). It is a shrub with a sprawling habit, that grows as long wiry stems that intertwine with itself as well as other species of scrambling plant, often forming impenetrable tangled masses. It has flowers that are pink or white and have a similar appearance to that of the rose, hence one of its names, "native rose". Another plant that has spectacular red, yellow and white flowers is the Richea scoparia, a tall spiked shrub that grows in thickets. Yet another plant that makes walking difficult.

Another unusual plant that is present in the high country, both plains and forests, is the pandani (Richea pandanifolia). It seems out of place in Tasmania as it looks very similar to a tropical palm, though it belongs to the heath family. It grows to between 4 and 9 m, and it is topped by a slender grass-like leaves that can reach as much as 1 m long. It usually has skirt of dead leaves draping down on the trunk, The appearance of this tree, with the skirt of dead leaves, usually around the lower part of the trunk, would not look out of place on a tropical island.

The highest altitudes are the realm of the alpine herb fields, including a cushion plant vegetation. This vegetation type is comprised of plants from a number of unrelated genera such as Pterygopappus, Abrotanella, Gaimardia and Donatia. These plants tend to grow in low, compact  clumps of mixed genera, with intertwined shoots. The mounds can vary in size from small to more than 1 m in diameter. They tend to grow on the most exposed peaks, where they dam the small streams of meltwater from the snow, and as the water finds another path, they dam that as well, leading to a series of small gardens with a waterhole, dispersed amongst the snow. When they flower the appearance of a garden is increased.

Sources & Further reading

  1. Helen Grasswill & Reg Morrison, Australia, a Timeless Grandeur, Lansdowne, 1981

Links

  1. The Tasmanians: Part 8b: Archaeology and the Oldest Tasmanians
Author: M. H. Monroe
Email: admin@austhrutime.com
Last updated: 24/05/2010

 

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading