Alpine and Subalpine Environment

See also: Alpine and Subalpine Plant Communities

Introduction

A Pandini fern covered in snowAlpine 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.

The Plants

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.

Colourful heath, Ricea scopariaAreas 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.

Geological framework

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

Cushion plant damageMost 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 minimal impact bushwalking.

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.

Contact

Natural Values Conservation Branch
134 Macquarie Street
HOBART TAS 7000
Phone: 03 6165 4319
Email: NaturalValuesConservation.Enquiries@dpipwe.tas.gov.au

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