IS THE CONVENTIONAL APPROACH TO KARST AREA MANAGEMENT APPROPRIATE TO TROPICAL AUSTRALIA?
l New South Wales National Parks and Wildlife Service, P. O. Box 2115, Queanbeyan, NSW. 2620; 2 Queensland Department of Environment and Heritage, P. O. Box 38, Chillagoe, Queensland. 4871
Abstract
Australia has a wide variety of karst styles ranging from the Nullarbor semi-arid/arid karstland, the very young syngenetic karsts in aeolian calcarenites, the 'conventional' impounded karsts of the Eastern Uplands from Tasmania through to the Texas area in southern Queensland and to a whole suite of karsts north of the Tropic of Capricorn across the whole of Northern Australia. Some of these latter are in wildly differing settings.
Many of the tropical karsts are fundamentally different from the impounded karsts in that they stand 'proud' of the surrounding terrains or cover vast areas with the input waters, usually groundwaters, being drawn from enormous areas. What thinking we have done about karst management has been from a perceived northern hemisphere perspective of maintaining catchment conditions at all costs. Such an approach has relevance to the impounded karsts, and to many of the syngenetic areas. However, it probably has little, if any relevance, from a karst process viewpoint, to the management of the Nullarbor or to the Barkly Tableland or to other karstlands in tropical Australia and, perhaps, to some of the karst areas in the Northern Hemisphere.
This paper reviews the karst styles of Australia, conventional approaches to karst management and discusses the relevance of traditional views to the management of the northern, tropical, karst resource.
It is argued that traditional approaches are inappropriate given the extreme difference in scale, the dramatic influence of the annual swings from semi-arid/arid to seasonally moist conditions and perhaps the lack of disturbing influences. It is suggested that we do not have an appropriate model for maintenance and management of karst processes in northern Australia. We are not concerned, in this paper, with visitor management.
INTRODUCTION
Management of karst areas has two major thrusts. Firstly, managers must address the maintenance of the karst environment and of karst processes — that is, land use management questions — broad-acre questions. Secondly, one must look at the actions of users and their direct impacts — that is, site-specific questions. This latter direction raises issues that are probably common across all types of caves and karst. There will obviously be local or regional sensitivities which require different approaches. The broad-acre questions are commonly thought of as having a common basis but it appears that local environmental settings make preconceived management approaches injudicious. Whilst this is probably the case with all karst areas it has become apparent that southern Australian perspectives, developed in the impounded karsts, need a radical rethink in Northern Australia and perhaps for other areas such as the Nullarbor.
As Elery Hamilton-Smith has put it in recent discussions:
'...managing Chillagoe is like managing an archipelago. There are islands of critical importance and management needs; there are islands of less significance. The seas between the islands are rich in resources and have many influences on the islands and vice versa. Where does one begin and the other end?'
This paper discusses the various karst styles across Australia and their management needs and the approaches taken in the past. We argue that the 'traditional' view of total catchment management derived from an Australian interpretation of European and North American karst management scenes. Australian karst management has been based on the (usually small and easily defined) impounded karsts of southeastern Australia. How often have we seen statements like 'careful management of catchments is the first principle of effective karst management' (Spate 1987, p4).
We argue that such an approach, however desirable, is not applicable to Northern Australia because of the settings, enormity and the environmental conditions which have shaped and operate today in these regions. The views of Sweeting (1972) on tropical karst are relevant to our claim for 'specialness' of tropical karst as will be discussed below.
Australia has a voluminous cave and karst management literature probably running to hundreds of documents yet few of these have addressed substantively the very real management issues outside the impounded karsts (see for example the Cave Tourism and Management Conference proceedings, the many consultancies conducted by the Australian Speleological Federation Inc., by ACKMA and many others and by the many and varied submissions made by individuals and organisations). No attempt has been made herein to review these.
Discussions of the management (as opposed to the conservation) of the very many extensive karst areas north of the Tropic of Capricorn are very few (see, for example, Anon 1990, CCNT 1990; CSS 1992a 1992b; Flett 1988, Gillieson 1993, Hamilton-Smith et al 1975, 1989). The areas are remote, are not subject to intense user or land use pressures and seem robust. Management has not been seen as an issue. However, the tropical areas are increasingly being used for recreational caving, for eco-tourism and there are pressures from mining in some areas as well as concerns arising from the spread of exotic species, the impact of grazing and from the alteration of fire regimes. There have been many papers dealing with the conservation of northern karsts with almost all dealing with Mount Etna. Whilst conservation can only be achieved through proper management; accounts of conservation campaigns are not, or only rarely, discussions of management requirements and methodologies.
With the exception of Davey (1978), Hamiton-Smith et al (1989 and the resultant CCNT (1990) plan) and the Mount Etna issue (for example, Sprent (1970), Pure (1977) or Hardy (1993), previous discussions have concentrated on visitor management. Whilst appropriate visitor management practices may well be required to conserve karst resources there are wider questions. We have tried to address some of these for tropical karsts. Similar papers could well explore the relevance of 'traditional' karst management models to such compact, but large, regions as the Nullarbor or to the string of aeolian calcarenite karsts around the western and southern fringe of the continent.
OVERVIEW OF AUSTRALIAN KARST STYLES
In spite of the views properly expressed by Jennings (1983a) regarding the paucity of karst in Australia there are a number of areas of great interest spread across the continent. The size of these areas varies widely and there are important differences in lithology, setting and other environmental parameters. When this paper was first conceived the situation appeared simple with Chillagoe-Mungana and Mitchell-Palmer (referred as Chillagoe-Palmer herein), Katherine and the Limestone Ranges of the Kimberley being the 'standards' by which tropical karstlands in Australia were to be judged — a few minutes reflection will demonstrate that the Barkly Tablelands, Lawn Hill, Gregory and other areas are very different to our original standards.
A brief outline of the karst types of Australia is given in Spate (1989) and a discussion of the all important carbonate aquifers in the same volume (Smith 1989). For the purposes of this discussion we will consider the following karst styles (Gillieson and Spate in press):
- the impounded karsts of the Eastern Highlands (broadly from Tasmania through to Texas in Queensland although there are outliers to the north)
- the karst of the Gambier and Nullarbor regions
- the syngenetic karsts in the aeolian calcarenites of the southern and western coasts
- the tropical karsts (broadly Mount Etna, Chillagoe-Palmer, Lawn Hill, the Barkly Tableland, Gregory National Park, Katherine, Limestone Ranges and Cape Range)
The Impounded Karsts
The impounded karsts are found in rocks of early to late Palaeozoic age and are associated with the Eastern Fold Belt. They are usually of a few tens or hundreds of hectares in extent but there are larger exceptions which have similar management problems to the broad acres of the north (the Molong-Wellington area, for example). It is these areas that we are most familiar with in a management sense and they contain very many valuable and significant sites and features. Whilst we may not be managing them in an appropriate fashion we do have a reasonable understanding of how they work and what management principles should apply. We have Kiernan's admirable little book (1988) as a bible. In this regard it is interesting to note that of Australia's 25 show cave operations only one, Yarrangobilly, has its catchment totally within a conservation reserve although Marakoopa comes close to achieving this goal.
The Horizontal Karsts
The karsts of the Nullarbor and Gambier regions are of (differing) Tertiary age but have some similar features in that they are of enormous extent, are in relatively soft, horizontally bedded limestones in which the phreatic waters are of very great importance to the karstification process and to the human communities which live on them. They differ greatly in their climatic regime with the Nullarbor being semi-arid to and and the Gambier area being very much wetter. The water table is much closer to the surface at Gambier and again has implications for both the karst and the people.
We probably know how to manage these areas - avoid water pollution, don't drain the lowlands (not relevant on the Nullarbor!), preserve the native vegetation and manage cave visitors as well as we can. The Nullarbor, in particular has had some discussion of its broad-acre management (Davey and Spate 1990, Davey et al 1992, Gillieson and Spate 1992, Gillieson 1993, James et al 1991). For southeastern South Australia a comprehensive bibliography is given in Hamilton-Smith and Spate (1996).
The Syngenetic Karsts
The syngenetic karsts fringe the coastline south from about Shark Bay in Western Australia right around to western Victoria. There are small patches on the Bass Strait islands and on Lord Howe Island. Jennings (1968) coined the term to describe karst found on the partially consolidated aeolian calcareous dunes deposited at times of lower sea level (i.e. during glacial maxima). These karsts have many distinct features — the most striking of which is the development of karst features in partially consolidated and very young rocks. Jennings (op cit.), Bastian and Susan White have written widely on these karsts (1964; 1991 and 1989 respectively, for example); these authors should be consulted for details of forms and processes.
These karst areas have many management problems especially as they are prone to groundwater pollution because of their lateral extent, topographic position and because of their very high permeability. In Western Australia, in particular, they are very important for water supply. Groundwater abstraction in the Augusta and Yanchep areas has produced a number of changes in caves in these areas (Bastian 1991; Ron Spackman pers. comm.). The karst of the aeolian calcarenites deserves a far more holistic approach to management than it has received in the past.
The Northern Karsts
The karst areas north of the Tropic are discussed in more detail in the next section. Suffice it to say, there are strongly contrasting styles and settings, land use and management issues. In this discussion we make no mention of Australia's most westerly karst area, Christmas Island, given that its oceanic setting is far removed from the setting of the bulk of Australia's tropical karstlands. With a rainfall of about two metres a year it is hardly arid or semi-arid in character as are the other areas.
As we came to appreciate in developing this paper, it is in some ways misleading to even think about the tropical karstlands as a single entity. The carbonate rocks in which they are found range from the Cambrian dolomites of the Barkly Tableland through to the orogenic Tertiary limestones on Cape Range. Most are very large in areal extent, the hydrological interconnections above and below ground are complex and the rocks vary greatly with the degree of exposure with much of the Barkly Tableland thickly mantled by soil and other sediments. The Chillagoe-Palmer in Queensland and the Limestone Ranges of Western Australia are at the other extreme with soil cover absent from most of the karst. The one unifying feature is the strong seasonality of the climate with most areas being seasonally and with a short 'wet' season characterised by short duration, high intensity rainfall events. Cape Range is definitely and with some seasonality.
Many of the areas stand 'proud' of the non-carbonate rocks and it is this fact which makes consideration of their management different from that of the impounded karsts of the Eastern Highlands. The major exception is the Barkly Tableland where relief is subdued due to the sediments mantling the surface. However, along the Tableland's north-eastern margin, in the Riversleigh-Lawn Hill area, the cover has been stripped and a super-imposed drainage network has cut down through the karst and produced karst which more nearly typifies our norm.
AUSTRALIA'S TROPICAL KARSTLANDS - HOW ARE THEY DIFFERENT?
Tom Aley (1994), during an impromptu speech at the Jenolan impounded karst, observed in reference to his immediate surrounds that 'the caves were in the wrong place' - that is, in the bottom of the catchment. There are design alternatives...
As evidence for the strong differences between tropical karst and other types, Sweeting (1972) devotes three chapters to karst types around the world. The first discusses types and processes in 'true' karst (holokarst), fluviokarst, gladokarst and nival karst areas. Relict and buried karsts, pseudokarst and similar issues are discussed in the third chapter. The second and longest chapter is devoted to tropical karstlands, wet, semi-arid or arid. Australia's tropical karstlands present us with a range of caves and karst settings that are geographically, topographically, climatically and some even geologically different from what we like to think of as the 'norm' (Jennings 1969).
Before discussing the differences between Australian tropical and non-tropical karsts it is valuable to briefly review the characteristics of each of the major areas north of the Tropic as they are not well known.
Cape Range, Western Australia
Cape Range is the only Tertiary orogenic limestone in Australia. Limestones of this type are the host rocks for much of the most interesting karst in the world. Cape Range has also had a most interesting climatic history having originally been a rainforest environment which is now decidedly and (Humphreys, 1993, Wyrwoll et al 1993) except in the odd years when cyclones exert their influence. Evaporation exceeds rainfall by a factor of ten to fifteen and karstification in today's conditions is extremely slow, and episodic, in the vadose zone. However, karstification in the phreatic and epiphreatic zones may well be comparatively rapid (by comparison with the vadose). Common ion and ionic strength effects and mixing corrosion are probably enhanced. Australia's only vertebrate troglobites are found here (Knott 1993) as well as a number of highly significant invertebrate taxa (see a number of papers in Humphreys 1993 but particularly the summary by Main (1993)).
The Range is an anticline in Miocene limestone with a system of relatively well developed caves — clearly formed at times with a more effective rainfall (Allen 1993). Two distinct cave ecosystems are present. The first is in the crest of the anticline where essentially 'dry' caves have existed since the Miocene to Early Pliocene preserving rainforest relictual species. Karst in the surrounding coastal plain supports a rich aquatic fauna which has probably evolved in response to sea level changes during the Pleistocene (Wyrwoll 1993).
It is clear that the area is of considerable significance on an international level. However the integrity of the karst and its dependant ecosystems are threatened by groundwater abstraction, limestone mining, infrastructure development which includes the North West Cape military communications establishments; marinas and caravan park development (Gillieson 1993, Hamilton-Srnith et al 1996). Main (1993) provides an admirable and succinct summary of the karst management issues here and how they might properly be addressed.
The Limestone Ranges of the Kimberley, Western Australia
The Limestone Ranges are one of Australia's most dramatic karst features. The Ranges are an exhumed barrier reef stretching for some hundreds of kilometres; they are analogous to the Great Barrier Reef and many of the reef features seen off Queensland's coast can be seen in the hard grey limestones of the Kimberley. The reef is of Devonian age and the limestones rise abruptly from the surrounding plains sometimes for as much as 110 metres. There is little in the way of limestone pediments; streams of super-imposition cut across the limestone (at Ceike and Windjana Gorges, for example). Surface karst features are extremely well developed and there are many caves. However, integrated underground drainage systems are not well developed although some examples do exist. What relationships the karst might have to regional groundwaters is not immediately obvious. Jennings and Sweeting (1963), Jennings (1983b), Playford and Lowry (1966), Nicoll (1977), Davey (1978) and Gillieson (1993) provide a background; the latter paper discusses some of the management issues.
The karst appears little threatened although the probable escalation of tourism activities may well have direct effects on caves and cultural sites associated with them.
Gregory National Park, Northern Territory
The Gregory karst is developed in the Supplejack Dolomite Member of the Skull Creek Dolomite Formation which is in turn overlain by sandstones (Storm and Smith 1991, Dunkley 1993). Although small scale phreatic karst development may take place beneath the non-karstified units, as subjacent dolines are evident, karst development is retarded until these units are stripped off. Well developed karst forms are found in and on the 10-15 metres thickness of the Supplejack Dolomite. There is also a superimposed drainage network. It would appear that the karst is a 'typical' tropical Australian karst in that it drains freely. In this case, at least, with the karst development restricted to the relatively thin Supplejack Dolomite any integration of the karst with the local groundwater regime would be very tenuous.
The area is not yet well known; it has a strongly seasonal climate and karst development occurs over an area perhaps 100 kilometres long. The caves are of significance to the Aboriginal people and sites of many types abound. Nothing is known of other values.
The Canberra Speleological Society which has conducted most of the exploration of the area (CSS 1992a, 1992b) raises various visitor management issues. It is not known whether there are broader management problems.
Katherine, Northern Territory
There are extensive areas of karstified limestone around Katherine with the best known areas being at Cutta Cutta and Kintore south and north of town respectively. The limestones are of Ordovician age and there are well developed cave systems and surface karst features. The karst appears as low outcrops rising abruptly from the surrounding plains which are probably soil covered pediments. Twidale (1984) interprets the landscape as an exhumed ocean floor but more recent explanations have apparently been advanced (as yet not published). Hamilton-Smith et al (1974, 1989) have discussed both the setting and its management needs.
The limestone bluffs and their caves, which often open out from the bluffs at plain level, act as recharge areas for regional groundwaters over a very large area. A number of the caves intersect the water table and contain a rich aquatic fauna. Groundwater pollution, associated with urban development and military bases, and changed fire regimes may threaten some aspects of karst in this area.
The Barkly Tableland, Northern Territory and Queensland
This area is set within Australia's largest groundwater basin (the Georgina Basin, Smith 1989; this area should not be confused with the Gregory National Park karst. Grimes (1988) provides a brief overview of the area. The karst is developed in both limestone and dolomite of Cambrian age and over much of its extent it is mantled by thick soils and other sediments probably largely of Tertiary age. In its north-eastern extent the sediment cover has been stripped off by the headward retreat of a number of streams and spectacular karst landscapes are exposed at Colless Creek, Lawn Hill and Riversleigh. Where the sediments cover the carbonate rocks, karst development is subdued or, more probably hidden. Some caves reach up through the sediment cover and accept enormous volumes of water during the wet season. Hamilton-Smith (pers. comm.) tells of a large tree wedged tens of metres into the roof of Kalkadoon Cave and of seeing aerial photographs of a lake several kilometres long occupying its entrance doline.
The karst is thus a recharge area in some places, a sealed system in other parts of the groundwater basin and, in the northeast, a discharge area. At Lawn Hill and Colless Creek the karst resembles the areas such as the Kimberley and Chillagoe-Palmer which stand proud of the landscape. Riversleigh, with its abundant evidence of former caves dating from Miocene times (Archer et al. 1991), perhaps more nearly resembles the relict nature of Katherine or of the impounded karsts than other northern areas. Karst management issues here include the possible impacts of mine de-watering on subterranean aquatic ecosystems (Peter Home, pers. comm), fossil collecting and tourism activities. Sensible management approaches for the Barkly region are perhaps the most complex of all Australian karst areas because of the thick sediment mantle.
Chillagoe-Mungana and Mitchell-Palmer, Queensland
The Chillagoe Formation is a long, curved strike-belt of sediments, stretching some 200km from north of the Palmer River to south-east of Chillagoe, in the base of Cape York Peninsula. Within this formation, large isolated blocks of steeply dipping limestone occur. Both angular and rounded tower karst, and low, pavement outcrops are found. The landscape is very striking with the towers, known locally as bluffs rising abruptly from the surrounding landscape. The limestones are Silurian-Devonian in age and most are dense, massive and relatively homogenous (Fawkner in CCC 1982). The karst belts of the Mitchell-Palmer and Chillagoe-Mungana localities total about 60km in length with a maximum width of 8km (Ford 1978).
The surrounding landscape is of low, rolling metamorphics, intrusive granites and isolated volcanics (Willmott and Trezise 1989) largely supporting tropical woodland savannah while vine thickets cling to the fire protected environment of the limestone bluffs. Surface drainage is well developed, while the groundwater system is undefined, and seems somewhat chaotic. The limestones and surrounding rocks clearly vary very wildly in their water bearing capacities. The limestones display well developed surface karst features at a wide variety of scale and extensive cave systems — mostly above the level of the surrounding plains. Some of the limestones have been re-crystallised into marble which has weathered to the rounded towers.
Both the marble and mineralisation associated with the metamorphism have supported mining industries. The area is subject to broadscale cattle grazing. Three of the Chillagoe caves have been developed as show caves. A number of other caves have been used as show caves in the past and there is recreational caving over most of the belt. The caves support significant bat, swiftlet and invertebrate communities. Many caves are clearly of significance to Aboriginal people.
Current and potential threats to the integrity of the Chillagoe-Mungana karst arise from mining activities, altered fire regimes, groundwater pollution and groundwater abstraction (Spate 1994) and it can be assumed that similar factors need to be considered for the Mitchell-Palmer to the north although the remoteness of the latter area means that pressures are far less. Additionally, the direct impacts of increasing commercial and recreational utilisation must not be overlooked.
Broken River, Queensland
The Broken River karsts are a group of six clusters of limestone outcrops some 150km west of Townsville. The limestones are of roughly similar age and origin to those at Chillagoe and the outcrops are correspondingly similar in appearance with the notable difference that gorges incise the karst at two locations. The geology is complex with folding and faulted landscapes and diverse rock types (CCC nd). As at Chillagoe some re-crystallisation to marble has occurred but extractive industry has been restricted to alluvial gold mining. The area is sparsely settled by miners and graziers. Values include bat nursery caves, swiftlet colonies, a cave considered worthy of 'Geological Monument' status, extensive reef fossil beds and sites of significance to Aboriginal people.
In common with the Chillagoe area, the climate is strongly seasonal, with a summer concentration of rainfall followed by a long, dry winter period. The ongoing academic discussion revolving around whether changing climatic patterns or the strong seasonality of the climate has been the major factor in the developments of Chillagoe's extensive cave systems and secondary deposits (Robinson 1977) could presumably also pertain to this area and its relatively undisturbed nature might therefore be of enormous value to future studies. Threats are most likely to come from mining activities, and to a lesser extent, the effects of grazing and altered fire regimes.
Mount Etna-Limestone Ridge, Queensland
Although there has been a great deal of investigation of the Mount Etna-Limestone Ridge area as well as very active conservation campaigns there is little substantive written on the area. Sprent (1970) provides the best background. The area stands above the surrounding plain and displays an extensive range of surface and subsurface karst features. The climate here is generally wetter and not as seasonally developed as the areas discussed above. However, there is enough seasonality to produce the now familiar swing from a long dry season to a period with more intense pluvial activity.
It is clear that the karst here presents a wide range of karst values being an important refuge for rainforest flora owing to the partial protection afforded from fire by the nature of karst. There are also important bat colonies, invertebrates and probably significant Tertiary-Quaternary fossil deposits.
Other than Hamilton-Smith and Champion's (1975) book, discussion of management has centred around limestone quarrying issues. However, fire, impacts associated with grazing and other agricultural pursuits and possible groundwater contamination as well as visitor use may also present problems. Some of the area is protected with a national park and a management plan is in preparation which will address some of these issues on part of the site.
Discussion
Although it has been shown that some considerable variation exists even within the northern karst, one universal influence is the strong seasonality of climate, specifically rainfall (Jennings 1969). During past glacial events the seasonality may have been more pronounced and it may well have been drier across much of the north (Grimes 1988). Rainfall occurs during summer, and the falls recorded between December and March may exceed 85% of the yearly rainfall as is the case in the Limestone Ranges (Nicoll 1977). Further, as Grimes (op cit. p 16) points out in the case of the Barkly karst 'the effectiveness of the rainfall is limited by its summer incidence and by the fact that much of it falls in thunderstorms followed by hot sunny conditions' (that is, when evapo-transpiration rates will be highest). Nicoll (op cit.) reports rainfall at 450-600mm with evaporation rates of 2500mm. So whilst the caves can be expected to be seasonally wet, they are also seasonally dry — often for a longer period in the yearly cycle. There is also a very large year-to-year variability.
In those areas where the karst stands substantially proud of the surrounding topography — Cape Range, Limestone Ranges, Chillagoe-Palmer, Broken River and Mount Etna/Limestone Ridge and the northeastern edge of the Barkly Tableland — this seasonal aridity is emphasised by very high rates of natural air circulation and the perched nature of the cave systems which very rarely reach the (dry season) water table. Large karst windows and daylight chambers are a common feature of these caves. The extensive and well developed cave corals point to high levels of evaporation. Similarly, the massive speleothems such as stalactites and stalagmites often have a micro-crystalline, chalky appearance due to the same effect.
Having caves 'high and dry' like this, also puts them largely out of reach of what is touted as the single greatest influence on our caves, and the greatest binding force in the link between the surface and subsurface environments - water movement. Very few of the tropical caves have permanent streams or even standing water. Very few have more than very ephemeral streams. Most water movement is in the form of seasonally rising and falling water tables as a result of rapid, but brief infiltration events. Surface drainage patterns may be well developed and are often superimposed being relics of former surfaces overlying the carbonate rocks.
Characteristic tropical karst surface features are common - large grikes, kamenitza, rillenkarren, spitzkarren and razor-sharp aretes are examples. Also noteworthy is the very high incidence of well developed phytokarst in daylight chambers.
The towering nature of many of the karsts tends also to support fire-sensitive vegetation — testimony to the fire-protective nature of the steep, soil-free and thus understorey vegetation - free, rocky slopes. The same characteristics protect these areas from the influence of agriculture and silviculture. Howarth (1993) points out the vital role that environmental stresses such as seasonal drought play in the evolutionary and selection processes which lead to the development of specialised forms in cave populations. Thus we should see a high degree of endemism and good examples of cave adaptation in our tropical caves. Cape Range, Katherine and Chillagoe-Palmer (and the Undara Lava Tunnels) do have highly significant invertebrate faunas (Howarth 1988; Howarth and Stone 1990, Humpphreys 1993).
The other areas have not yet been examined in adequate detail but it is known that at Riversleigh, for example, there are significant aquatic faunas possibly under threat from de-watering of huge open cut mines (Peter Home, pers. comm.).
So, while the caves of the tropical north may or may not be closer to being in the 'right' place, to use Aley's terminology, they are certainly subject to a different suite of influences, and thus present managers with a different set of challenges, than do the more conventional caves of the impounded karsts.
CONVENTIONAL APPROACHES AND PRINCIPLES OF KARST AREA MANAGEMENT
World-wide, the management of karst areas revolves around the minimisation of human impacts - both direct, in the forms of tourism, recreational caving and scientific study; and indirect, such as the effects of agriculture, forestry, mining, road building, altered fire regimes, hydroelectricity development and other alterations to natural hydrologic regimes, residential development and waste disposal. Kiernan (1988) presents a very useful discussion of many of these impacts.
Paradoxically, it is the site-specific or direct form of impact which is the more commonly identified and managed, while the broad or indirect impacts on karst environments and processes are neglected (being in the 'too-hard' basket). These, sometimes subtle, influences are often the more far-reaching impacts.
Published material relating to Australian karst management has to date focussed, understandably, on the better known and documented areas, particularly in New South Wales, Victoria and Tasmania -- where the people are. As Spate (1989) points out "this depth of study is largely the result of the peculiar population distribution in which the majority of Australians live southeast of a line between Newcastle and Adelaide. Most of the [studied] karsts also lie in that area." With the exception of a few isolated examples and of the Mount Gambier/Western Victoria karsts on horizontal Tertiary limestones or on Quaternary aeolian calcarenite, most are impounded karsts.
The nature of these small, impounded karsts means that they are strongly influenced by disturbances within their catchments, and hence we are presented with such doctrines as:
The fundamental principle of karst management is that the whole catchment must be considered in managing a karst resource because of the high degree of integration between surface and sub-surface environments (TASNPWS 1994, p 19).
This catchment management precept has been thoroughly explored and documented by Kiernan (1988). His explanation of the factors to be considered in the proper management of karst is a further development of the broad maxim simply expressed in terms of four principles expounded by Worboys and Butz (1979) - maintenance of the hydrology, meteorology, geology and biology.
Using the four principles as a basis for discussion, traditional karst management can be summarised as follows:
The Hydrological Principle
This underlines the necessity to allow natural infiltration patterns and flow regimes to occur unimpeded — physically, chemically or temporally. It is axiomatic that water is the principal agent in the development of karst landscapes, both in the solution of bedrock and the development of speleothems, tufa terraces and the like. However, it has been the norm to assume that the same, or similar, hydrographic conditions are evident today in the landscape as in the past. This is clearly not the case. Indeed karst forms are one of the better warehouses of the evidence for climatic change.
Karst landforms are characterised by chaotic drainage, caves, gorges and residual hills, and by a high degree of integration between surface and sub-surface environments. Attention must be focussed on the maintenance and monitoring of sinking and rising points for water, maintenance of vegetative cover, avoidance of the diversion of cave streamways, abstraction and contamination of groundwaters by chemicals, biological agents and sediments.
The Meteorological Principle
This concerns the movement and relative components of the air within cave systems, with the dual underlying intents of maintenance of a 'natural' state and protection from pollutants. Caves are generally considered to have quite limited windows where light enters and gaseous exchange with the outside atmosphere takes place. Experience has shown that even minor alterations to the physical conditions affecting these key areas can have far-reaching effects on the relative levels of light, water vapour and component gases in the cave atmosphere. Of these, the levels of humidity and carbon dioxide are considered key factors, due to their critical roles in the dissolution of carbonate rocks, the deposition of speleothems and the distribution of cave fauna.
Cave desiccation due to interference with airflows is often a management problem. Airborne detritus (e.g. lint) is also a concern due to its ability to adhere to speleothems and other cave surfaces.
The Biological Principle
Both the surface and underground biology of karst areas are recognised as distinctive, often having strong associations with specific environmental conditions. Disproportionately high incidence of endemism is exhibited by some cave faunas compared with surface communities. Once again, we are urged that 'Careful management of karst catchments is important to proper cave conservation and particularly so where important cave fauna is present.' (Kieman 1988, p 38). Emphasis is placed upon the quality of water in cave streams, alteration of water flow regimes and/or routes, and direct human impacts such as light, noise and trampling affecting cave biology; and fire, flooding and other modifications of hydrologic regimes, surface water quality, grazing and clearing affecting surface biology.
The Geological Principle
Although easily dismissed as being robust and unchanging, the geological features of a karst landscape are both vulnerable and dynamic. Erosion, weathering and sedimentation are natural processes, all subject to human modification. The effects of fire, trampling, mechanical damage and removal, and artificially induced erosion may be evidenced upon the surface geomorphology, and trampling, specimen collection, mud entrainment and altered sedimentation are some of the threats to the integrity of the sub-surface environment. The geological principle demonstrates interrelatedness of the four principles with many of the issues highlighted above having obvious overlap.
ARE THESE APPROACHES AND PRINCIPLES APPLICABLE TO AUSTRALIA'S TROPICAL KARST?
We have argued, either directly or by implication that a whole-catchment approach to the management of Australia's tropical karstlands is irrelevant or impracticable because of scale, problems of catchment definition, lack of coupling with groundwater and, most importantly, because of the fact that we are dealing with two different environments — an active, often short wet season as opposed to a long and static dry. Different processes are affecting the karst, caves and biota in these two seasons. It is probably relevant to re-examine the four principles in light of tropical conditions.
The Hydrological Principle
The basic tenet of unimpeded infiltration and flow regimes is sound, but when dealing with karst which exhibits complex hydrological interconnections, little cave stream activity, short duration, high intensity rainfall events, seasonal aridity and very high evaporation rates both in surface and subsurface environments, we need to look more closely at the prevailing natural hydrological cycle, and seek its maintenance, through management, where necessary and where possible. For example, in many cases a stronger focus on determining the extent of local 'natural' water table fluctuations, and human influences on these, is needed. The impacts of silviculture and agriculture appear minimal in Australia's tropical karsts, but other land use practices such as mining, eco-tourism and manipulation of fire regimes perhaps require more detailed assessment. The vast catchment areas for many of these karsts, combined with only tenuous surface-to-subsurface relationships makes pure catchment management more challenging.
The Meteorological Principle
The tropical karsts in general, with exceptions such as the Katherine, Cape Range and Barkly karsts, tend to have caves with well-developed air circulation systems, and resultant high evaporation rates. This feature is exemplified in tropical tower karst. In this context, cave desiccation is not a major management problem, but rather, a feature of the natural status quo.
Airborne detritus of the cave-visitor borne variety is an extremely low priority issue partly because of relatively low visitation rates.
Of rather more concern is the issue of dust raised by the passage of visitors in caves which subsequently settles on speleothems. Such dust has the potential to transport fungal spores and other pathogens with the possibility of infecting humans, or previously uninfected parts of the cave system. This is the equivalent of a combination of the mud-entrainment and the lint problems of the wetter and cooler caves. In some cases the problems require immediate redress. However, the high levels of aeolian dusts naturally occurring during the dry season may outweigh the role of visitors.
Tropical karsts may well have larger fluctuations in carbon dioxide levels than those which pertain in temperate areas because of the on/off nature of biogenic carbon dioxide production between wet and dry seasons.
The Biological Principle
That the surface and underground biology of karst areas is distinctive, and often vulnerable is indisputable. The significance of the catchment, while reduced, remains relevant in terms of natural water table levels, for example. Beyond this, emphasis should perhaps be away from hydrology, and we need to seek the factors most affecting the biology of our tropical karsts - largely on a case by case basis. The direct human impacts on cave biology will largely be similar to other karst types, as mentioned above. Other factors that may have considerable local impact are altered burning regimes, grazing, mining and biocide applications as they do in temperate regimes.
The Geological Principle
This is the most universally applicable of the four principles and the generalised intent to protect the geological record, and geomorphological features and processes deserves to be upheld. It is incumbent upon the managers of tropical karstlands to be ever vigilant for threats against this objective (and all others), which may take forms previously unsuspected, and thus undocumented.
CONCLUDING REMARKS
The above discussion serves to highlight the distinctive elements of tropical karst and indicates that appropriate management directions can be derived through consideration of the four fundamental principles and their application to a set of conditions which differs from those prevailing in other karst environments. However, it is clear that the intensity of processes is much higher in the tropics. The full influence of seasonal fluctuations, which tend to dominate our thinking, is probably not adequately understood. The apparent lack of boundaries to the systems also presents a mental hurdle to a holistic understanding of whole systems.
It may well be that tropical karsts are environments that we can look to as models for ideas about the role of climatic and other environmental fluctuations on karst areas which are apparently more uniform. Howarth (1993) provides some examples of comparisons of this type. For example, he describes what he terms the "tropical winter effect" which helps explain the distribution of obligate cave invertebrates in tropical caves. In his words:
"The tropical winter effect is based on two factors: since tropical caves are warm, limestone solution and evaporation rates are high; and since the night time surface temperature in the tropics usually falls below the cave temperature, nocturnal drying winds enter the caves" (p. 66).
This entire discussion reinforces the need to have a basic understanding of form and process in a number of geographic areas and across a variety of scientific disciplines if one is to successfully manage karst resources wherever they may occur.
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