Pandani, the world's tallest
plant (Photo by Steve Johnson)
Alpine and subalpine areas occupy a small proportion of Tasmania's land surface but carry a very important and attractive part of our flora. Most of the mountains are in the western half of the state (the exception is the Ben Lomond National Park in the northeast), where they are subject to ice-laden storm winds, high rainfall and low winter temperatures, although snow seldom lies for more than a few weeks.
The highlands support many species found nowhere else in the world, the proportion of endemic species increasing as you go west and reaching a maximum near 70% on the West Coast Range. Many of the species belong to the Antarctic Gondwanan association, in which our plants shared a common ancestry with plants from New Zealand and South America in the ancient supercontinent of Gondwana.
In most Tasmanian alpine areas there is no distinct treeline, with the hardiest eucalypts, the snow gum (Eucalyptus coccifera) growing wherever if can find shelter close to mountain tops or forming open woodlands on the best-drained parts of alpine plateaux up to altitudes of 1300m.
Coniferous forests and shrubberies are less able to cope with extreme exposure but are also less widespread than the eucalypts because they can only recover extremely slowly from fire. There have been a number of very big wildfires in western Tasmania in the last 200 years.
The colourful heath, Richea scoparia
(Photo by Steve Johnson)
Areas exposed to storms from the north-west and west, particularly where the bedrock is such that mineral soils have not been able to develop, usually carry treeless moorland in which hardy grasses and sedges predominate.
Where rough topography provides shelter, drainage is good and soil can accumulate, alpine vegetation is dominated by heath and shrubberies in which woody plants prevail. Many of these, such as scoparia, provide spectacular displays of colour.
It is a feature of Tasmanian alpine areas that there is great variation in the vegetation over short distances - several distinct plant communities will commonly occur together in a mosaic, with sharp boundaries between coniferous shrubberies with rainforest affinities, short woody heath under snow gums and very short sedgelands or herbfields.
Any discussion of plant communities would be seriously incomplete without mention of the geological processes which have shaped, and continue to shape, the environment upon which plant communities are based. Tasmania's biogeographical heritage has played a major role in determining the nature of the State's plant (and animal) communities, while the underlying bedrock and soil type are critical to species compositions.
Tasmania has had a turbulent geological history over the last 700 million years with three periods of deformation (deep folding or block faulting) and four periods of igneous activity interrupting the processes of erosion and sedimentation.
The eastern edge of the alpine area (just west of a N-S line drawn through the middle of Tasmania) is dominated by dolerite, a dark crystalline rock which rose as a liquid and solidified high in the Earth's crust about 150 million years ago. As it cooled the dolerite cracked into vertical columns which were revealed as erosion removed the covering of sedimentary rocks. The columns now form cliffs but also rough land surfaces where rocks weather to mineral soils fairly high in plant nutrients.
Central western Tasmania is underlain by sedimentary rocks, the oldest of which are folded and deformed to give small but extremely rugged quartzite mountains such as Frenchmans Cap. Around this mass are mountains formed from gently folded massive sandstones and conglomerates, as seen on the West Coast Range and Mt. Roland. The youngest sedimentary rocks are flat lying, often thinly bedded mudstones and sandstones which form high, rounded ridges between the dolerite mountains. All these sedimentary rocks are rich in quartz and are very poor providers of mineral soils. They contribute very little in the way of nutrients and the vegetation has adapted to survive on peat soils derived from plant remains. Sheltered niches are available in the rugged quartzite mountains where shrubberies can develop, but on the open ridges tough sedges and grasses do best.
Threats to Alpine Areas
Despite their hardy appearance,
cushion plants are very fragile
and can be easily damaged by
(Photo by Steve Johnson)
Most alpine areas in Tasmania are protected with in National Parks or the Tasmanian Wilderness World Heritage Area. The exception is the West Coast Range, where a rich alpine flora on siliceous conglomerates is unreserved.
The greatest threat to alpine plants is fire; some of the climax species may take between several hundred and several thousand years to regenerate from fire, and about one third of the Tasmanian highlands have already been damaged this way.
Other threats are posed by trampling, particularly in wet moorland and herbfields. Even cushion plants, which appear to be very hardy, are in fact very fragile and can be easily destroyed through trampling. Bushwalkers should avoid trampling over sensitive alpine areas, and observe the principles of Leave No Trace - a set of guiding principles that help minimise our impact on the places we visit.
In the harsh alpine environment disease is not usually a problem, although some fungal pathogens persist to the highest altitudes and cause damage to susceptible species.
Where to visit alpine areas
Dolerite mountains, with their heathy and shrubby communities, are easily visited as day trips inHartz Mountains National Park,Mt. Field National Park and Ben Lomond National Park. Mt. Wellington has both alpine and lower altitude floras reduced and modified by frequent burning (the last big fire was in 1967) but still displays many plants found only in Tasmania. The Central Plateau is crossed by the Lake Highway near its northern edge and side trips may be made into the grassland/heath country round Lake Augusta and Lake Ada.
A wide array of plants dependent on quartz-rich bedrock are easily seen on day walks round Cradle Mountain, while the five-day traverse of the Overland Track (Cradle Mountain to Lake St. Clair) provides a wealth of scenic and botanical experience. Remote quartzite mountains such as Frenchmans Cap are more difficult to reach but all display a wealth of plants, many of which can only be seen in the Tasmanian wilderness.