KARST MANAGEMENT IN COMMERCIAL FORESTS
Only a small proportion of Tasmania's caves and karst lies within national parks and reserves. Some 60-80% lies in areas of State Forest, and other important karst areas are private land. Many karsts are areas of multiple land use and are rich in a diversity of resources besides caves. As a result the safeguarding of important parts of the karst heritage demands appropriate management of terrain that is not formally protected. The nature of karst is such that the sorts of practices that will help protect caves are also the sorts of practices most facilitative of a long term future for the use of some other resources, such as the soils and water supplies. Management of unreserved areas can also be important to the well being of cave reserves that have been arbitrarily defined such that stream or dripwater catchments are not included within the boundaries.
In this paper I wish to briefly look at some of the interactions between karst processes and human use of the karst at Mole Creek in Tasmania, to illustrate some of the problems and some of the needs. I wish then to focus on the question of commercial forestry operations on karst and some recent progress that has been made towards improving the management of commercial forests in karst areas. My perspective is the management of karst as an environment that offers multiple resources and for which there may be multiple demands. I deliberately relegate caves to being merely one of these resources and possible uses.
Mole Creek
The Mole Creek karst consists of approx 260km2 of Ordovician limestone that crops out along the foot of the Great Western Tiers in central northern Tasmania. The area has been settled for over a century, and its economic base is farming and forestry. Mole Creek is also highly scenic and there are two tourist caves. Despite being a developed area, there is still considerable potential for further cave discoveries. Many caves are already known, including such celebrated systems as Herberts Pot and Kubla Khan. Land tenure is now a complex mosaic of private land and State Forest, with some small cave reserves and other areas of Crown Land.
In the early 1970s the Southern Caving Society proposed that a major reserve be created to safeguard the complex system of caves associated with the Mole Creek itself, a system which lies at the eastern extremity of the limestone belt to which it gives its name. Around the same time I proposed in a submission to the National Estate enquiry for the Southern Caving Society that in such areas there was a need for overall karst management plans. In 1980, Joe Jennings made representations to the then Tasmanian National Parks and Wildlife Minister supporting the reserve proposal. In 1982, the Tasmanian Conservation Trust nominated virtually the whole karst belt for inclusion on the National Estate list.
The Australian Heritage Commission sought comment on the values of the area from Joe Jennings, and then in September 1984 listed an area of approx 8,000ha. However, the Tasmanian Forestry Commission wished to establish commercial forests in the area. Due to the conflicting aspirations of the National Parks and Wildlife Service and the Forestry Commission, I found myself employed by the Division of Engineering and Operations in the Tasmanian Forestry Commission in 1984, armed with a car, a torch, 400km2 of terrain to map and 12 months to report. My brief was to evaluate any direct or indirect consequences of forestry operations on karst, to develop management principles for the karst, and to identify features worthy of conservation. The study was jointly sponsored by the Commission and NPWS, with some funding drawn also from the Australian Heritage Commission.
Twelve months seems a long time until you're faced with a task of this complexity and an area the size of this one. Nonetheless, the study resulted in a three-part draft report. Part A was a review of the nature of karst, its values and its vulnerability. Part B attempted to develop a reconnaissance inventory of the area, which was divided into eight sub-basins. Maps were presented of the bedrock geology, Quaternary geology, surface and underground karst, forest types and land tenure for each of these sub-basins, with an accompanying text that also addressed the karst values, system relationships, slope stability and human impacts. Part C focussed on the role of the Forestry Commission state-wide as a karst land manager. It also proposed draft guidelines for roading, logging and forest maintenance on karst.
And so what sort of human impacts were revealed at Mole Creek? The study revealed an ignorance of karst by land managers of all kinds. Sinkhole dumping by the local council and by farmers was a common problem. Bacterial contamination of streams, some used as water supplies, proved quite serious with coliform counts of over 30,000/100ml revealed in some cases. The fouling of sinking streams by stock also contributed to the high level of contamination.
As far as forestry was concerned, there were problems related to logging slash being dumped in sinkholes and cave entrances. There was evidence of accelerated ground subsidence in some logged areas, probably due to the reduced transpirational uptake of water after cutting having permitted increased flushing of the fines from the soil mantle into cavities in the limestone. Sudden collapses of similar origin occurred in some pasture areas, often to the distinct detriment of stock that were standing there at the time! Accelerated sinkhole formation due to concentrated run-off from impermeable road surfaces was also revealed, sometimes to the detriment of the road.
Erosion of thin residual limestone soils at rates of up to 200 times the fastest conceivable soil regeneration rate was also evident in farming and logging areas and in some cases total soil loss in the near future was a definite threat. Silt swept into caves was diminishing the quality of the underground waters.
Silt washed into sinkholes plugged outlets in the sinkhole floor leading to the flooding of extensive areas of pasture, rendering them inaccessible or unsuitable for use for long periods each winter.
Landslides also proved to be a problem, not so much on the limestone where moisture was evacuated underground fairly rapidly such that high pore water pressures seldom developed in the soil mantle, but in other parts of the karst catchment areas. Many of the mantles consist of solifluction sheets that crept downslope due to a high moisture content during cold climatic conditions prior to 10,000 years ago. Many have become stable since the climate ameliorated due in part to the advent of the new forest cover which increased the transpirational uptake of moisture and bound the mantle with its roots. Logging eliminates both these aids to stability, and road construction may remove toe support on slopes. Dealing with such problems demands hazard mapping and assessment, and some knowledge of the hazard period based on root-rotting times, regeneration growth rates and storm event return periods. The problem is exacerbated where bedrock benches perch moisture beneath the slope deposits. Mapping and interpreting the alluvial, glacial and periglacial mantles is critical in many of the karst management questions, such as potential soil erosion, water quality considerations and landslide risk. On top of all this, there were existing and potential problems of speleothem drying due to activities on the surface affecting seepage water, plenty of evidence of cave vandalism and problems with existing reserves in terms of boundaries and adjoining tenure. What still seems needed in karst areas such as Mole Creek is an integrated programme of karst management related to natural rather than artificial cadastral planning units. That is a tall order in itself. It is made the taller by our lack of detailed information even on a karst as celebrated and populous as Mole Creek, where, for instance, during the 1984 survey it was still possible for a new outflow cave to be found within 100m of a barbecue site at a cave used by tourists for nearly a century, and for the previously insignificant Mersey Hill Cave to turn out to be the second longest cave at Mole Creek, after Herberts Pot and ahead of Kubla Khan and Croesus.
The inventory problem in unroaded virgin native forests, in some cases still in a wilderness condition, is obviously very much greater.
Some impacts of logging on karst
In Part C of the Mole Creek karst forestry report I focussed on the role of the Forestry Commission statewide as a karst manager, and argued that in view of the national importance of some of this karst estate the Commission had national responsibilities. I argued that there was a need for an adequate karst forest data base that covered both inventory and process information, and for a defined karst management policy and standards of operation.
Foresters have had a long association with caves in Tasmania. It was the foresters and timber cutters of late last century who first came upon such celebrated caves as Exit Cave and Mystery Creek Cave, and at an administrative level they created reserves to protect some of these places. With the expansion of the pulpwood industry in the 1940s and 1950s, most notably the advent of the Australian Newsprint Mills Ltd operation in the Junee-Florentine area, road networks and clearfelling facilitated the exploration of many more caves. Bodies charged with protecting important natural areas, established firstly under the Scenery Preservation Act 1915 and later under the National Parks & Wildlife Act 1970, progressively took over cave protection. However, in the 1970s the Forestry Commission formally established its own system of forest reserves, that grew to include the Julius River Caves in far NW Tasmania, and nearby Lake Chisholm, a serene karst lake.
The "Mt Field Caves" (presumably Growling Swallet) appear to have been considered in defining, in 1916, the State's first national park. But only 30 years later 1,600ha of the park was revoked and handed over to Australian Newsprint Mills Ltd. Forestry operations spread onto more of the limestone country and in 1966 spot fires spread into the Mt Field National Park from the ANM concession. The state government accepted a company offer to extend logging operations into burnt-out areas of the park, to remove the 'fire risk' posed by fire felled timber. There was soil erosion and there were landslips, with more than 1m of sediment blocking access in one cave within 12 months of logging (Richards & Ollier 1976).
In 1970, when Tasmanian cavers were exploring Tassy Pot, then the deepest cave known in Australia, we shared descent of the 50m entrance shaft with a terrifying array of plummeting logs and debris as a result of logging slash having been dumped into the entrance doline. There were also suggestions that the passage of heavy log trucks over one cave had damaged speleothems by vibration, and that others might be damaged by changes to groundwater seepage. Another charge levelled against forestry operations was that at Gunns Plains in NW Tasmania speleothems were being damaged by debris being washed through a tourist cave from logging in its catchment. But there was no hard evidence. And on the other hand there was an increasingly comprehensive network of private roads that could give cavers ready access to limestone. Half the recreational traffic through the ANM gate at Maydena is cavers.
There are some other possible impacts of logging on caves that are worth thinking about. What damage might be caused by diverted water should karst conduits be blocked by eroded sediment? Might flashier run-off from clearfelled areas imperil cavers? Might the increased aggressivity of seepage water due to increased biological activity in soils warmed after clearfelling (Goede 1981) lead to speleothem resolution problems? What adverse affects might there be on cave climates or speleothems if airflow routes become blocked? How many cave entrances are lost beneath the slash and sediment (Gunn 1978)?
What is the effect on cave fauna of silt or chemicals either spilt or applied for silvicultural purposes? Tasmania's cave fauna is heavily reliant on food washed in, and on the nightly migration outside of cave crickets. What is the likely affect of logging around entrances and along streams? It has also been suggested that the establishment of pine plantations has led to cave dehydration and adverse affects on cave fauna (AP Spate, pers. comm.).
So in summary, logging is known to have some serious impacts on karsts, and there are also a very large number of questions to which we need to start finding some answers.
Towards Change
I now wish to trace some of the steps towards change in the management of Tasmania's karst forests since the 1984 karst forestry report.
In 1984 the Commonwealth Government was preparing to consider the issue of new woodchip export licences for some Tasmanian producers. The woodchip companies and Forestry Commission were in a process of jointly compiling a draft Environmental Impact Statement (EIS) and it was possible to inject into this some preliminary information arising from the Mole Creek study. The EIS was released for public comment in February 1985. The EIS was a useful advance because it acknowledged the extent, significance and vulnerability of the karst in commercial forests, and the need to protect it. It recognised the need for, and gave a commitment, to integrated cave and karst management. It also gave a commitment that the proposed logging at Mole Creek, which had been halted until completion of the Mole Creek report, would stay halted until specific guidelines for logging in karst areas were formally adopted and decisions were made on any new reserves needed in the area. The final EIS adopted the same perspective, emphasising the need to protect water and soil in karst areas, and other values. The Commonwealth had both the EIS and the Mole Creek karst forestry report available to it in considering the reissue of woodchip export licences.
Following consideration of the EIS a Memorandum of Understanding was signed by the Australian and Tasmanian Governments on 12 June 1986. It provided for logging to be on a sustained yield basis; for appropriate botanical reserves; for identification and reservation of rare and endangered species; and for the proclamation of Forest Practices legislation. It was agreed that State Forest resource inventories would include karst, landscape and other values; that pre-logging surveys would be conducted by the Commission in areas on the National Estate list; and that forest operations would be planned and conducted to take account of these values, of soil and of water. The Memorandum included a commitment to processes for pre-logging identification of archaeological sites, geological features and other special natural features. The Memorandum was not a legally binding document, but sought resolution of disputes through consultation rather than coercive use of Commonwealth or State powers or perogatives.
An appendix to the Memorandum indicated that the Commonwealth export licences would exclude certain areas of the Southern Forests including karst areas at Mt Anne and the Weld Valley, and in the Cracroft Valley. Licences for the Mole Creek area would be conditional upon operations being conducted in accordance with special management guidelines. These guidelines were to be prepared taking into account the recommendations of the Mole Creek report and the views of the Commonwealth Minister for Primary Industry on protection of the National Estate Values. The licences would also be conditional upon Commonwealth views being taken into account elsewhere in SW Tasmania. Importantly, while this constrained operations for woodchip export it did not constrain operations for domestic use. Nonetheless it appeared to be an advance, at least until the advent of the 1986 ANM plan for logging of karst areas including the upper Weld Valley and others unrelated to the woodchip EIS which made no mention of karst, karst hazards or karst values in the areas involved.
On the other hand, the forthcoming plan for the Southern Forests may be sensitive to karst.
Conflict subsequently developed between the Commonwealth and State in respect to the Southern Forests and Lemonthyme Forests, relations have broken down and the Commonwealth has threatened to block logging by resort to its external affairs powers that relate to the World Heritage Convention. This is based on an interpretation of the World Heritage operational guidelines that it argues compel it to protect the integrity of listed sites from damaging activities outside their boundaries, and to protect sites of World Heritage quality whether or not they are listed.
The IUCN officer responsible for World Heritage matters has visited the State and the IUCN has reported to the Australian Government that extension of the existing World Heritage area is desirable. This recommendation cited in particular further cave discoveries in the Maxwell River Valley, and it proposed boundaries that include extensive areas of karst, some of them in areas of potential for hydro-electric development as well as forestry. Legislation to block logging in National Estate forests has passed the Federal Parliament and been proclaimed, but the State has indicated that it will not comply with the Federal Law. The stage is set, unfortunately, for a High Court battle between the Australian and Tasmanian Governments, and for conflict in the forests.
On the more positive side, forest practices legislation has been proclaimed in Tasmania as agreed in the Memorandum. The Forest Practices Act 1986 seeks to ensure that timber is harvested in an environmentally acceptable manner, and places considerable emphasis on education. It provides for mandatory timber harvesting plans wherever timber is to be commercially harvested, and a Forest Practices Code that provides a set of basic environmental standards. Logging contractors, landowners and timber companies buying the wood can be fined for commencing operations before a plan is approved, or departing from the approved plan. The code covers planning for harvesting, building access, harvesting, regeneration and forest health. It was officially released by the Tasmanian Minister for Forests in early May 1987.
The Forest Practices Code makes specific provision for karst in forest planning and operations. It prescribes that all logging in karst catchments will be planned to take account of karst values. Thus, it acknowledges the need to consider the catchment area and not just the limestone outcrop. It acknowledges the need to apply the highest standards of roading and harvesting procedures to minimise the alteration of karst water movement patterns, including the need to avoid areas with obvious surface seepage. It acknowledges the importance of mantle materials to erosion hazard, and upgrades the status of residual limestone soils from low erosion risk class to high erosion risk class for commission purposes. It acknowledges the need for hazard mapping in road planning, and for pre-logging archaeological surveys.
The Code prescribes that there should be no dumping of waste materials in depressions and sinkholes. It prohibits the poisoning of flora and fauna adjacent to cave streams and cave entrances. It specifies that karst features and protection measures be identified in timber harvesting plans, preparation. It addresses such things as methods of log loading, prescribing small landings well removed from karst reserves and depressions, and prohibits all but boom type loaders in karst areas.
At a more detailed level, the Code differentiates, between karst areas where soils are developed on thick mantles of materials dumped on the limestone by glaciers, streams or slope movement, and those where thin residual limestone soils are present. Where transported materials are present the code restricts earth moving operations during periods of heavy rain and for 'necessary' periods thereafter. It applies wet weather limitations on logging; sets a maximum size of 200ha for clear-cut coupes; prescribes cable logging where slopes exceed 35%; prescribes integrated snig track and road planning to reduce soil disturbance; and prescribes high drainage standards in post logging restoration. More rigorous controls are imposed in areas of thin residual limestone soils. In such places earth-moving operations are restricted to the dry season, must be suspended during wet weather, and special attention to drainage is required. Logging is to occur only during the dry season, and is to be suspended during wet weather. Clear-cut coupes must, henceforth, be kept 'small', with a short fall-line dimension. Uphill cable logging systems are demanded for slopes of 15-35%, with no logging to occur on slopes of greater than 35%. The Code demands that snig tracks should not cross any shallow caves, enter any karst depression, or divert a natural watercourse. The Code demands that all known sinking streams, intermittent or ephemeral surface channels, caves or sinkholes must be avoided during logging operations. It prescribes high drainage standards for post-logging restoration, and effective sediment traps on landings. No slash burning is to take place on slopes in excess of 20%.
The forest practices legislation is now law in Tasmania, and the Forest Practices Code is part of it. It applies to the 60-80% of Tasmania's karst that occurs within State Forest, and to privately owned forest at places like Mole Creek, Loongana, Gunns Plains and elsewhere. Its effectiveness in improving their management remains to be seen, and will be dependant on such things as the diligence that is displayed during compilation of forest resource inventories, and the level of reason displayed in implementing the prescriptions. The Code appears to represent a major advance, but this is often the stage at which advances are lost. The means, be it gaining legislation or a national park, too often gets confused with the goal, that is, improved karst management or nature conservation. We now have the means in our grasp, but its not a time to relax if the real goal is to be attained. Coupe size, prescribed slopes, prescribed burning, reserves and assessment procedures, all need further consideration and there is a need to remain vigilant to ensure that the code does not just become a statement of good intentions, but really does achieve the major improvements in the management of karst forests that are so badly needed.
References
GOEDE, A (1981) Variation in the hardness of cave drips at two Tasmanian sites, Helicite 19(2):56-67
GUNN, J (1978) Karst Hydrology and Solution in the Waitomo District, New Zealand. Phd thesis, Univ. of Auckland
KIERNAN, K (1984) Forestry Operations and the Mole Creek Caves. Australian Heritage Commission Library, Canberra, 320pp
RICHARDS, AM and OLLIER, CD (1976) Investigation and Report of the Ecological Protection of Exit Cave near Ida Bay in Tasmania. Report to Tasmanian NPWS. 72 pp