Timber harvesting on karst lands: some operational considerations and procedural requirements
ENDINS, n." 13. 1987. Ciutat de Mallorca.
TIMBER HARVESTING ON KARST LANDS:
SOME OPERATIONAL CONSIDERATIONS AND
PROCEDURAL REQUIREMENTS
by Kevin KIERNAN (*)
Resum
En ernprendre el desenvoluparnent de zones carstiques, els tecnics en gestió forestal es troben
arnb la preocupació pel rnedi arnbient i arnb uns especials problernes practics. Durant la fase opera-
cional cal fer uns acurats ajusts. S'ha de parar especial esrnent al drenatge i al disseny, localització i
mantenirnent dels carnins. És necessari prendre precaucions especials durant I'extracció de troncs i
en la localització i ús de les instal.lacions de carrega de troncs. Aquí avancarn unes propostes estu-
diades per reduir I'irnpacte ambiental associat arnb el procés de tala als boscos de les zones drsti-
ques de Tasrnania. Aquestes propostes poden tenir una aplicació rnés arnpla o adaptar-se a medis
carstics onsevulla s'ernprengui I'activitat fustaire.
Abstract
The forest Manager is confronted by special environrnental concerns and practica1 problems in
seeking to develop karst areas. Carefull adjustments need to be made at the operational stage. Par-
ticular attention must be given to drainage and road design, road location and road maintenance.
Special precautions need to be taken during log extraction and in the location and utilisation of log
loading facilities. Specific proposals are advanced that have been designed to minimice the adverse
environrnental effects associated with the process of timber harvesting in Tasrnanian karst forests.
These rnay have wider potential application or may be adaptable to karst environments elsewhere
where logging activity is undertaken.
Karst landscapes result frorn the dissolving of
protection of water quality and the natural drain-
soluble bedrock by acidic natural waters, and are
age pattern - if strearns becorne silted it could
characterised by predorninantly underground drai-
lead to caves being blocked or underground wa-
nage systerns; underground caverns; surface de-
ter supplies being darnaged perhaps rnany ki-
pressions (sinkholes); dry creek beds; large springs;
lornetres distant;
sinking strearns and other landforrns. Because
protection of the natural processes or airflow
such landscapes cornmonly offer a variety of eco-
between caves and the outside world;
nornic, scientific and recreational resources, and
protection of a zone of natural vegetation around
because these are often highly sensitive to distur-
cave entrances - cave dwelling organisrns rnay
bance or darnage, forestry operations must be con-
be dependent upon this for their food supply.
ducted with extreme care. At al1 times very high
priority should be accorded to:
- protection of the soil and its abiliw to store
Roading
and transrnit water;
(a) The principal environmental concerns in karst
forest roading lie in the risk of soil erosion; block-
(*) Departrnent of Geography.University of Tasrnania (forrnerly
Division of Engineering and Operations, Forestv Cornmis-
age of underground drainage channels by sedirnent;
sion, Tasmania).
drainage diversion; cave air flow diversion; increas-

ing public access to sensitive caves; overstressing
Road Design
thin cave roofs; diminution of water quality; and
structural damage or damage to cave decoration
With the above considerations in mind, road
by shock wave production during construction or
designers should take account of the need to:
by vibrations during road use (Kiernan 1984).
1. await the completion of karst inventory and as-
(b) The practica1 problems posed for the roading
sessment procedures along the road route and
authority by karst include the presence of deep rifts
i n its general vicinity prior to the commence-
i n the bedrock or complexly fluted and undercut
ment of design work;
surface outcrops; ground surface instability includ-
2. plan to construct roads only in fine weather and
ing occasionally the possibility of collapse or wash-
ensure that earthworks are stabilised as much
out; road subsidence due to sinkhole development
as possible, particularly prior to any cessation
(sometimes actually induced by the drainage chan-
of work for 48 hours or more or when rain is
ges caused by the road itself); and difficulties with
expected;
highly irregular bedwork topography leading to un-
3. wherever possible, keep road width to a mini-
predictable foundation depth (and strength) beneath
m u m to reduce the area of permeable mantle
overburden. Where sudden collapse has occurred,
converted t o an impermeable surface which
i t tends less often to be due to bedrock failure than
will promote runoff rather than infiltration;
t o the failure of overburden after fines have been
4. consider leaving roads across unmantled lime-
flushed out of it and into hidden solution cavities in
stone country unsealed to slow runoff, unless
the limestone (Aley et al 1972, Kiernan 1984).
siltation is a hazard;
5. balance cuts and fills to the maximum possible
(c) The possible hydrological and water quality
extent to avoid dumps of unused fill which may
impacts of roads (Parizek 1971) inclucie:
be washed into karst channels;
1. the beheading of aquifers in soil and sha-
6. not construct roads across unstable sites such
llow bedrock;
as active sinkhole margins or slip zones; to
2. the development of groundwater drains
ensure assessment of mantle stability before-
where cuts extend below the local water
hand; to consider adopting an alternative rou-
table;
te or leaving the particular location unharvest-
3. changes in ground and surface water di-
ed where necessary;
vides;
7. utilise full bench construction in critica1 situa-
4. the reduction of infiltration rates beneath
tions;
the road and associated drains;
8. bring in any extra fill needed from outside the
5. the reduction of streambed infiltration
karst area concerned or from sites where the
where sedimentation has occurred;
karst is very heavily mantled by transported
6. the silting of channels causing flashier run-
surface deposits;
off or flooding;
9. ensure that roads do not enter any karst reser-
7. changes in runoff and recharge characte-
ves apart from necessary crossings of stream-
ristics generally;
side reserves where bridges are present;
8. erosion and reduction in recharge areas
10. anticípate survey and design for karst roads;
and on flood plains;
11. keep batter angles low where erosion suscep-
9. the obstruction of groundwater flow by
tibility is high and siltation of underground karst
abutments and retaining walls;
channels is a risk; and to minimice the extent
10. changes in water chemistry where new
and angle of exposed soil and the duration of
bedrock components are exposed (e.g.
exposure.
more acid drainage if pyritic rocks such
as pyritic shales in limestone are exposed);
Drainage Design
11. pollution by petroleum, silt or other ma-
terial~.
In order t o safeguard soil and water values the
(d) The risk of mass slope failure is increased
following steps are recommended:
where road cuts are excessively steep or designed
1. ensure that silt traps are provided downstream
profiles exceeded; where roads cut below the local
of bridgeworks or in other situations where
water table; where roads truncate the toe of pre-
there is a risk of karst stream siltation; and en-
viously stabilised transported mantles; where
sure there is adequate access to enable the
there is an increase in the pore water pressure of
traps to be periodically cleaned and the sedi-
previously stable areas due to diminished transpi-
ment placed in a position where there is no risk
rational uptake resulting from removal of adjacent
of it regaining access to the stream;
vegetation; where roads incise steep slopes below
2. ensure adequate drainage and stabilisatio
convex breaks of slope; or where works are poorly
during al1 stages of construction;
drained (Kiernan 1974).
3. consider catch drains above cuttings to mini-

mise their erosion by surface runoff; line any
9. t o minimise the clearing of vegetation beside
steep portion, disperse water into soil or grade
roads consistent with allowing the road surface
t o culvert; the drains should be designed so as
to dry satisfactorily;
t o minimise the localised entry of water into
10. not to leave excess ballast in a position where
the soil profile and consequent risk of slope
it may be eroded either during or subsequent
failure;
to construction;
4. ensure table drains are of adequate capacity;
1. not to permit ballast or any form of debris to
5. drain outlets to side drains, culverts, water-
enter any cave entrance; karst reserve; signifi-
courses or soaks at a spacing in accordance
cant sinkhole; active or inactive watercourse;
with the criteria for high erosion risk class soils
draughting hole;
on bare karst, and according to the nature of
12. to stockpile soil for later revegetation wherever
the mantle in karst catchments;
necessary and to revegetate construction tracks
5. provide for sediment traps to be installed on
as soon as they are no longer needed;
al1 surface watercourses (permanent or ephe-
3. to plan the location of snig tracks in conjunction
meral); where streams enter nearby caves the
with road planning, bearing in mind those con-
trap should be sufficient to minimise the influx
siderations which are suggested in the karst
of material down to silt grade;
logging guidelines.
7.
disperse runoff at bridges into vegetation rat-
her than directly into the stream; construct
Road Maintenance
bridges only when the risk of high flows is li-
mited; properly bridge permanent, intermittent
(a) It is absolutely fundamental that al1 silt traps
and ephemeral channels; contain the road sur-
be regularly inspected and cleaned; access for
facing material to the bridge; and emplace silt
cleaning and a safe site for debris dumping
traps downstream during construction;
should be established beforehand.
8. minimise any modifications to the catchment
( b ) All drains should be regularly inspected and
size or runoff characteristics of sinkholes when
kept clear, particularly after logging ceases.
planning road drainage;
\\c) Roads to be put to bed should be outsloped,
9. site sediment traps some distance downstream
drains cleared, water barred, blocked to traffic,
from the disturbance to maximise the length
also ripped and re-seeded if necessary; moni-
of natural channel available to absorb some
tored.
of the sediment.
( d ) Consideration should be given to eliminating
a road no longer in use if a sensitive cave exists
Road location
close by and an effort to minimice excessive
visitation appears warranted.
The following safeguards may be particularly
(e) Signposts referring to karst features should be
important in karst areas:
installed only after detailed consideration of
1. t o await the completion of karst inventory and
the implications by the karst specialists.
assessment procedures before attempting to
(f) Maintenance should be kept up on roads to be
finalise road location;
retained; some roads may need to be gated to
1. t o fit roads t o the topography in an effort to
limit misuse or excessive access to sensitive
minimice the infilling of sinkholes and genera-
sites such as baseline karst process monitoring
Ily minimise earthworks by adhering to topo-
installations.
graphic form;
3. t o avoid unstable slopes, erodible soils, sink-
holes, active or inactive drainage routes,
draughting holes or cracks in the ground;
Logging operations
4. not t o locate roads over the top of caves and
t o minimice road construction over probable
1. No forest operations should commence until
underground drainage corridors along which
the distribution and nature of the various karst
caves probably occur;
resources of the area has been mapped and
5. t o ensure that sidecast material cannot reach
assessed.
watercourses or sinkholes;
2. All planning with respect to road and snig track
5. t o avoid steep slopes where runoff is more dif-
locations and drainage should be in amordance
ficult to control;
with the provisions of the Karst Management
7.
t o respect al1 karst reserves and to maintain or
Policy.
establish buffering vegetation to filter runoff;
3. No logging operations should commence until
8. t o minimise stream crossings and interference
the planning of any necessary karst reserves
with natural drainage;
or other special safeguards has been finalised.

The following general guidelines should be followed:
b) where only thin residual limestone soils
are present neither wheeled nor flexible
1. No logging should occur on steep limestone
tracked skidders should be used on lime-
slopes.
stone slopes of even moderate angle; only
2. Logging of limestone slopes of more moderate
highline systems hauling upslope or sky-
angle should only occur during the driest
line systems should be permitted on slopes
months, in very small and dispersed units;
steeper than about 10" and no logging at
logging should be curtailed with any unseason-
al1 on such slopes steeper than about 20°.
al onset of wet weather when water runs in the
3. Snig tracks warrant particular attention because
table drains.
they frequently destabilise the soil, concentrate
3. All karst reserves should be respected. These
and alter the surface drainage pattern, and re-
exist not only to protect environmental values
present sites of soil compactiun which alters
but also t o safeguard forest workers in areas
the balance between water running off the soil
prone to ground subsidence or collapse.
and the water which soaks into it.
4. These should be no felling of trees towards
4. Planning of snig tracks should aim to reduce
any karst reserve, cave entrance or water-
the length, density and gradient of snig tracks
course; sinkholes should also be avoided es-
and should occur concurrently with road plan-
pecially where they are known to contain a
ning.
cave or stream.
5. Cross drains should have been planned in ad-
5. No form of rubbish, debris or toxic material
vance to disperse rather than concentrate run-
should be permitted to enter any sinkhole,
off, reduce water velocity and minimice sedi-
watercourse or cave entrance; no insecticides
ment transport. Some of these cross drains
should be allowed to settle in any natural ve-
should be activated whenever track use is
getation zones outside cave entrances.
interrumpted for 48 hours or more or if heavy
6. Where silt traps are installed they should be
rain seems likely.
regularly inspected and cleaned when neces-
6. Because maximum ground compaction occurs
sary; the silt removed from the trap should not
after only a few passes, snig tracks should be
be placed so as to be at risk of being washed
limited in number to reduce the affected area
back into the stream.
but carefully sited with respect to karst land-
7. If further caves or streamsinks are discovered
forrns and karst reserves.
during logging the site should be avoided until
7. Snig tracks should be outsloped and if neces-
assessment procedures have been completed.
sary stabilised by fast growing grasses or le-
gumes after use; sediment traps should be
The following specific precautions are suggested
installed where required.
to minimise the risk of erosion and siltation
8. No snig track should enter any karst reserve
during logging operations:
or significant karst depression.
9. No watercourse should be used for snigging;
Log Extraction
no watercourse should be diverted to flush mud
from a snig track, or any other form of mud-
Because soils are most susceptible to damage
flushing undertaken.
when they are wet, and because underground
10. Snigging should be conducted in an upslope
karst water channels are most easily silted
direction to minimise downslope concentration
when runoff is prevalent, forest managers
of runoff in gouged channels.
should err on the side of caution in transferr-
11. lnadvertent water diversions should be dis-
ing logging from sensitive karst sites during
persed and the basic cause rectified.
winter.
12. Drain spacing for karst areas with thin residual
The often sensitive soils, risk posed to drainage
soils should be in accordance with high erosion
patterns by excessive silt in streams and the
risk sites; even where soils are thick they should
often rocky nature of karst means that particular
be managed as posing not less than a moderate
care needs to be exercised in the selection of
erosion risk.
extraction equipment -
13. In some cases it may be desirable to reduce
a) where karst assessment procedures have
log size in an effort to minimise the greater
identified the existence of a thick deposit
erosion potential posed by handling large logs.
of naturally transported earth and rock over-
14. To reduce ground vibration, logs should be
lying the limestone, logging operations may
suspended above the ground while being mo-
proceed normally but giving full regard to
ved over shallow caves.
the need t o minimice soil erosion and
15. All assessments of erosion risk should be made
stream siltation;
by the karst inventory assessors and based

upon the true field-verified character of the soil
Acknowledgements
and parent materials, not extrapolations from
bedrock geological maps.
This paper stems from a study which origina-
16. Cross cutting and debarking should occur at
ted in 1983 with financia1 support from the Tasma-
the stump to minimise the extent of necessary
niai i
Forestry Commission and Australian Heritage
landings, but bark and other debris should be
Commission and logistical assistance from the Na-
prevented from entering karst reserves and
tional Parks and Wildlife Service (Tasmania). 1 am
sinkholes etc.
grateful for assistance and useful discussions at
17. Where logs are used as sediment barriers it will
that time with Brendan Diacono, Phil Jackson, Steve
be necessary to clean the sediment out occa-
Harris, Elery Hamilton-Smith, the late Joe Jen-
sionally. If this is not done water may simply
nings, Paul Wilkinson and others. I am also grateful
overtop the log and erode back underneath it
t o the Director, Australian Heritage Commission,
through the development of a plunge pool. By
holder of copyright o,n the study, for permission to
this means the trapped sediment may even-
include here the work done at that time.
tually be realised as a result of drainage pas-
sing under the log.
Bibliography
Landings and Loading
ALEY, T.; WILLIAMS, J.H.; and MASSELLO, J.W. (1972): ((Ground-
water contarnination and sinkhole collapse induced by leaky
1. No landings should be sited close to any karst
impoundrnents in soluble rock terrain),. Miss. Geol. Surv.
reserve or significant karst depression.
Wat Res. Eng. Geol Ser 5.
FORESTRY COMMlSSlON (TAS) (1981): irGuidelines for the plan-
2. Landing size should be minimised and altera-
ning and control of logging in native State Forestsn. For.
tion of the existing topography minimised.
Com. Leaflet. 3, 33 pp.
3. Wherever feasible the surface soil should be
KIERNAN, K.W. (1984): «Land-use in karst areas: Forestry Opera-
stockpiled and kept free of logging debris for
tions and the Mole Creek Caves)>.
Australian Heritage Com-
mission Library, Canberra. 320 pp.
later restoration work.
PARIZEK, R.R. (1971): almpact of highways on the hydrogeologic
4. Winter landings should be corded and al1 land-
environrnentn. pp. 151-199 in D.R. Coates (ed). Environmen-
ings should be located on well drained sites.
tal Geomorphology and Landscape Conservation Dowden,
5. Landings in karst areas should be drained into
Hutchinson & Ross, Stroudsburg.
the surrounding vegetation or silt traps when-
ever wet weather threatens; this should occur
whenever operations on thin limestone soils
are suspended for 1 week or more increasing
t o one month or more on thickly mantled karst
catchments.
6. Within reason the original ground contour
should be restored as soon as possible after
logging ceases; if necessary landings should
be ripped and hand replanted. Operators should
bear this in mind and not unnecessarily disturb
stock piled soil.
'. Tracked front end loaders exert a significant
cutting action upon the soil and should only be
used where karst'is thickly mantled by soil and
of moderate angle. They should not be used
during wet conditions. Where the soil is thin
or the slope steeper (greater than about 10")
loading should only be by crane.
In addition t o the safeguards that are presen-
ted here and are aimed specifically at the protec-
tion of karst environments, normal sound logging
practices (eg. Forestry Commission 1981) should
be adopted.