A review of dipterocarps - Center for International Forestry Research

Management of Natural Forests
with properly planned and executed harvesting
operations, not only is the damage contained, but so are
the harvesting costs (e.g. Marn and Jonkers 1981).
Unlike the case with uniform (Shelterwood) systems,
selective fellings can cause considerable damage to the
future crop, the medium sized residuals. The damage
intensity and extent to both trees and soils vary with the
log extraction system used. Skidder-tractors are used
extensively. They cause more damage to the ground
surface, increasing soil erosion and retarding
regeneration and growth of residuals. With precautions
and improvements like pre-determined skid trails and
reduced vehicle movement, damage can be considerably
reduced. Logging on steep slopes (i.e. >15 o ), which is
very damaging, should be curtailed.
Besides damage caused by extraction, felling damage
too can be very intense, especially to the advanced
regeneration (Nicholson 1979). Directional felling and
pre-felling climber cutting reduce such damage.
Although this practice has been recognised as beneficial,
it is seldom carried out. Currently, several initiatives have
been started in reducing logging damage to the soils and
the residual vegetation under schemes called ‘Reduced
Impact Logging ’ (RIL). These initiatives are mainly in
Sabah (Marsh et al. 1996). In these RIL operations,
besides cutting lianas, directional felling and pre-planned
skid-trails, the operations are closely supervised so as
to minimise skid trail length and blade use. A 50%
reduction in all measures of damage was demonstrated
compared with conventional logging for an increase of
about 10-15% of direct logging costs.
High-lead yarding systems have been tried in some
concessions in the Philippines and Malaysia. They are
costly, difficult to maintain, and require well trained
crews to maintain them. Basically, selection fellings and
high-lead yarding are incompatible, as the residuals are
damaged considerably. There is also heavy damage to the
soil when trees are dragged uphill. However, skyline
yarding systems are beginning to show considerable
promise. With the simple skyline yarding where two spar
trees are used, road building is reduced. The other is the
Long Range Cable Crane System which uses a tight
skyline with intermediate supports and a carriage with
the log suspended to it vertically. The carriage travels
along the skyline and dumps the suspended log at the
head of the spar or tower. This has been tried in the
Philippines (Heyde et al. 1987) and Sabah (Ong et al.
1996). The original carriage could only lift small logs,
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but the new one introduced in Sabah can lift 5 tonne logs
(personal observation). The use of a skyline system
reduces road building considerably, and limits damage
to the soil and residual trees to a considerable extent.
The skyline systems hold the answer to logging of
dipterocarp forests of Southeast Asia.
Helicopter logging is now being tested in Sarawak.
This system remains rather expensive and dangerous. The
cost of keeping the helicopter in the air is high, and the
operations have to be perfectly coordinated: trees have
to be felled in advance, and the helicopter can only start
its operations when a sufficient number of trees are
available. The timber being harvested should have very
high value. Too many accidents have happened with
helicopter logging for it to be considered a viable
operation. There is also the problem of illegal logging
as it becomes much easier to steal timber using
helicopters, and the activities are difficult to control.
Failures in Implementation of Practices
It is obvious from the above review of silvicultural
practices, there is no lack of scientific methods for
managing the variety of dipterocarp forests. While
systematic management may be lacking (Leslie 1987,
Wyatt-Smith 1987), some kind of management is being
attempted for many of the forests in Asia; it is however,
mainly in the form of area or volume control. It was
reported that about 19% of the Asian region’s productive,
closed broadleaf forest is being intensively managed
(FAO 1981c). However, one can dispute if area and
volume control is management.
Several factors seem to hinder true management of
these dipterocarp forests. For one, it seems better to
cash in the timber market now than wait for uncertain
future markets. Next, there is a mismatch between
declared policy and implementation. Far too few
resources are allocated for management, while the rate
of logging is beyond what the forestry agencies can cope
with (Wyatt-Smith 1987). Some managers have adopted
the ‘minimum intervention’ approach on the argument
that there are still uncertainties in the value of some
silvicultural treatments (Tang 1987).
Forestry agencies are unable or unwilling to
implement the declared management policies, and
silvicultural prescriptions are always behind schedule,
or abandoned altogether. Panayotou and Ashton (1992)
present several cogent reasons for this: