A review of dipterocarps - Center for International Forestry Research

Management of Natural Forests
increment, and hence a cutting cycle of about 35 years.
From a quick perusal, it is obvious the realised growth is
far below that assumed. Furthermore, the wide variation
in growth rates between forests calls for more precise
local growth data for determining cutting cycles, and
national averages are inapplicable. Next, despite evidence
that silvicultural treatments of girdling and liberation
felling do boost the growth of the trees, this is rarely
undertaken. This of course has to be taken into
consideration with the costs of operations and the
benefits of increased timber production.
Enrichment Planting
Enrichment planting has been a tool in dipterocarp forest
management, and several dipterocarp species have been
successfully planted into natural forests (Barnard 1954,
Tang and Wadley 1976, reviewed in Appanah and Weinland
1993, 1996). It is indeed widely and variably practiced
throughout the Asian tropics. Such planting is considered
when the stocking of seedlings and saplings of desirable
species is inadequate because of poor seedling survival
or due to destructive logging methods. With the
modified-MUS of Peninsular Malaysia, enrichment
planting was supposed to be a standard practice: the
deficit in natural regeneration to be artificially
regenerated using dipterocarp wildings.
The success of such plantings was variable and
planting efforts have invariably declined. There are
several causes for this. Planting work is difficult to
supervise, seedlings have to be regularly released from
regrowth, and a regular supply of dipterocarp seedlings
is needed. Wildings can be used, but individuals differ
widely in their performance. Moreover it is costly (labour
demanding). As a consequence, the efficacy of
enrichment planting has been questioned (Wyatt-Smith
1963, OTA 1984).
Nonetheless, enrichment planting is receiving
accelerated attention as a possible technique under the
selective felling practices in Kalimantan (e.g. Smits
1993, Adjers et al. 1996). Extensive areas are being
planted up in Kalimantan with dipterocarp wildings.
Rooted cuttings have also been developed but their
success in the field has not been evaluated yet. Their root
structure must hold the tree during sudden wind storms.
Smits (in Panayotou and Ashton 1992) has in view a
model for enrichment planting of degraded dipterocarp
forests in Kalimantan. Such sites are to be first planted
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with an over-storey of building-phase species, and a few
years later with dipterocarps raised from cuttings and
inoculated with mycorrhiza. The fast growing species can
be harvested in the mid-term, and this will release the
dipterocarps for harvest in 50 years. One major technical
problem is the difficulty in harvesting the pioneer species
without causing excessive damage to the mature-phase
trees (Panayotou and Ashton 1992). There is also concern
for the bad form of dipterocarps raised from cuttings.
Wyatt-Smith (1963) pinpoints the conditions which
merit enrichment planting, and the silvical characters
necessary for species ideal for enrichment planting. The
characters include regular flowering and fruiting, rapid
height growth, good natural bole form, low crown
diameter/girth breast height, wide ecological amplitudes,
tolerance to moisture stress, and free of pests and
diseases. But most of all, the species should produce
timbers of high value.
All too often, enrichment planting is done without
consideration for the light conditions. Supervision and
follow-up maintenance are necessary, especially canopy
opening treatments. With care, enrichment planting
remains promising and viable. It has been successful in
Karnataka and several other Indian States, and Sri Lanka,
in both moist deciduous and evergreen forests.
While it is generally accepted that the best and
cheapest method for regenerating dipterocarp forests is
still using the natural regeneration, enrichment planting
has received a new boost particularly for badly degraded
forests. Under the ‘Carbon Offset’ Project, an American
utility company paid for planting dipterocarps in Sabah,
to offset its carbon dioxide emission in its power plants
in Boston (Moura-Costa 1996). This may appear
innovative, although its value will be confined to
rehabilitation programmes. Planting dipterocarps may be
viewed as a final resort, after natural regeneration
practices have failed.
Exploitation Damage
Good harvesting systems are critical for sustainable
management of natural forests. The harvesting should not
irreversibly compromise the potential of the forest. The
operations should never degrade it, and must also allow
for rapid recovery of the stand. Studies of logging damage
in dipterocarp forests begun in the late 1950s show that
it has been increasing with mechanisation (Nicholson
1958, Wyatt-Smith and Foenander 1962, Fox 1968). But