THE POTENTIAL SCIENTIFIC IMPORTANCE OF CAVES IN SOUTH-WEST TASMANIA: A CASE FOR THEIR PRESERVATION
INTRODUCTION
From a large universe of probable lines of scientific enquiry regarding South-West karst, I have briefly discussed only a few which present work indicated as promising. This paper is an attempt to sketch merely one case for the preservation of 43% of Tasmania's karst area. The South-West karst areas are of potentially significant value to science and should be preserved completely from the hydro-electric power developments which are their principal threat. Other threats are limestone mining and forestry. Forestry possibly affects soil and groundwater conditions and upsets underground insect ecology through disturbance of soil and plant litter outside the cave.
The emotional, aesthetic, recreational and other arguments for the preservation of the South-West region, including its karst areas, are compelling on their own and have been eloquently started by many others (for example: Neilson, 1975; Kiernan, 1975, 1977a, 1977b; Bardwell, 1978).
THE SOUTH-WEST AND TASMANIAN KARST
The South-West referred to is the area shown as a dashed line in Figure 2 and follows the Australian Conservation Foundation recommended boundary used in the Report of the South West Advisory Committee (1978).
The South-West is a coherent region whose force of sheer beauty derive from all its attributes - wild rivers, mountains, caves, buttongrass plains and lakes, to name a few. Separating out the karst however is not the fractionary and arbitrary exercise it first seems because proposed hydro-electrical schemes (Figure 2) would be underlain by 25% of known South-West karst area.
The structural geology in the South-West puts cavernous rocks at a disadvantage in hydro-electric schemes because they occupy topographically lower areas, while more resistant quartzites form ridges and mountains. The area of karst shown in Figure 2 is a conservative depiction. It is now known that there are other areas of limestone in the South-West. Therefore, the two percentages given above are correspondingly conservative.
Some of the major limestone and dolomite areas in the South-West include: the huge belts of limestone in the Gordon and Franklin valleys, belts in the Olga and Hardwood valleys and extensive outcrops of either limestone or dolomite on the Weld, Jane and Nelson Rivers, and at Precipitous Bluff, Bubs Hill and Mt Anne. New areas of limestone outcrop are still being discovered.
Figure 2: Showing the boundary of the South West,the distribution of Tasmanian Karst (after Goede, 1972) and potential hydroelectric impoundments.
POTENTIALLY FRUITFUL RESEARCH
- Archaeological
The culture of the indigenous Tasmanians was swiftly and mostly destroyed by about the 1840s and relatively scant knowledge remains of them. Contemporary accounts are limited and have almost yielded their maximum contribution to present knowledge. Further knowledge must come from archaeological techniques. The few such investigations done in Tasmania have revealed important evidence on the life of the Aborigines, some of the most significant information having come from excavations in two former sea caves and one limestone cave. The limestone cave excavation (Goede, Murray and Harmon, 1978, and Goede and Murray, 1977) in the Florentine valley revealed bone and stone Aboriginal tools in a limestone breccia which were dated from associated charcoal at 20650 ± 1790 yrs B.P. This means that Aborigines, at least temporarily, were at this high altitude inland site during the last Ice Age. This has raised intriguing questions on the relationship between Aboriginal man and caves in the Tasmanian past (Goede, 1977).
As yet unexplored caves in the South-West must be regarded as also possessing archaeological potential. They may be repositories of cultural material which date from glacial times when much of the landscape was probably a cold grassland.
- Geomorphological, Geological and Palaeontological
There are 3 main areas of enquiry under this heading to which caves in the South-West may yet contribute:
- Clues to past climatic conditions and variations may be gained from careful palynological and sedimentological analyses of undisturbed cave sediments. Caves in South-West karst may produce data sensitive to the climatic fluctuations of the past. This would be due to the region being adjacent to highland areas which have undergone pulses of glaciation in the past.
- In heavily vegetated areas, for example, the karst on the Olga, Gordon and Hardwood Rivers, interpretation of structural geology is more difficult because of limited outcrop. Careful mapping of cave systems can be useful in this respect.
Caves can provide an ideal preserving medium for bones, in colluvial material and breccias which can become isolated from weathering. Deposition of calcium carbonate affords further protection. Excellent bone deposits of probable great antiquity have been found in a number of caves in the South-West (Kiernan, pers. comm.).
- Faunal
The South-West has been traditionally acknowledged as having a scant vertebrate population (Guiler, 1965; Swain, 1972) due to the harsh climate and the lack of feeding opportunities in the buttongrass plains and rainforests which predominate in the region.
The invertebrates are an exception. The region has many types of environments rich in aquatic invertebrates (Swain, 1972). These environments include buttongrass plains, lakes, tarns and rivers. These features are all found on the South-West karst and it could be expected that lithogenic variations in the habitat give rise to interesting faunal variations between non-karst and karst areas. There is certainly a lithological contrast between the highly alkaline karst rocks and the highly siliceous rocks which dominate in the South-West.
Swain (1972) claims that the interest in invertebrate fauna in the South-West is not in species diversity but rather, in the uniqueness of a small number of species. He names two groups of Crustaceans with ancient lineage (phreatiocids and syncarids), representatives of both of which have been found underground in the region.
From a report on Exit Cave by Richards and Ollier (1976) it is tempting to extrapolate, and expect long species lists from other caves in the South-West. A total species list for the region, of insects recorded from underground, might be expected to be very high because it appears that cave systems even as relatively close to each other as are Hastings Cave and Exit Cave can have substantially different faunas (Richards and Ollier, 1976).
A wealth of entomological knowledge is bound to come from the South-West karst areas and the few collections yet made, indicate promise in this regard.
- Botanical
This field is hardly relevant to caves but from a karst viewpoint vegetation communities peculiar to alkaline rocks have been barely studied in the region. One study has been done by Kirkpatrick and Harwood (in press) at Mt Bobs. Jarman and Crowden (1978) found unusual plant communities on limestone bedrock in the Hardwood and Olga River Valleys. Closer botanical studies on karst (particularly where plant communities are to be found close to their alkaline bedrock rather than being rooted in thick acid peat) in the region will be valuable due to a paucity of such communities).
CONCLUSION
Hydro-electric impoundments are not the only threats to caves in the South-West. Forestry activity may disturb the cave ecology, mining can be disastrous, and both have threatened certain cave areas in the region until recently. Hydro-electric dams are a looming threat whose deleterious effect on karst in the region will be total obliteration of some areas. Huge areas on the Franklin and Lower Gordon Rivers may be destroyed - a quarter of the karst area of South-West Tasmania.
The potential knowledge to be derived from studies in caves and karst in these regions cries out for their preservation, yet these areas do not fall within any State Reserve.
REFERENCES
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Swain, R. (1972), The Fauna of South-Western Tasmania, Tasmanian Year Book No. 6: 1972, pp 56-64, Govt Printer, Hobart.