A review of dipterocarps - Center for International Forestry Research

Plantations 168
intervention. Sanger-Davies (1937) carried the ideas
further and formulated a guide for the tending of more
or less even aged stands of S. leprosula. In his technical
recommendations, he proposed starting tending while the
shelterwood is still standing.
When designing research it should be kept in mind
that the beneficiary of the thinning operation is the crop
tree and, therefore, indiscriminate elimination of noncrop
vegetation is unnecessary. Non-crop trees have
beneficial ecological functions. Mead (1937) discusses
the formation of mixed stands of dipterocarps and shadebearing
non-dipterocarp understorey species with dense
crowns. The species Scorodocarpus borneensis, Mesua
ferrea, Randia scortechinii, Randia anisophylla,
Greenia jackii etc. were planted in mixture with Shorea
leprosula, which forms a rather open crown, to prevent
the invasion of light demanding pioneer vegetation which
impede the establishment of natural dipterocarp
regeneration. Tending has, therefore, to consider also
the secondary vegetation. Any inconsiderate felling
should be avoided and instead it should be asked, whether
such vegetation could assist in keeping the forest floor
conducive to natural regeneration.
Re-establishment by Natural Regeneration
Embarking on plantations with dipterocarp species which
grow relatively slowly compared with fast-growing
exotics needs strong economic backing. Recent
economic calculations (Kollert et al. 1993, 1994) have
shown that it only makes sense, if at the end of the first
rotation the new stands are established by natural
regeneration. It is in this context that some comments
are given on regenerating naturally even-aged planted
dipterocarp stands, although on an operational scale this
will be only a problem of decades from now. Systematic
assessment of the regeneration situation and initiation
of natural regeneration procedures are urgently needed
for all species identified for plantation programmes and
for which stands near rotation age exist. This should
include research on the harvesting techniques required
to reduce negative impacts on stand regeneration.
The natural regeneration of even-aged planted stands
will most likely be carried out as some kind of
shelterwood system. Shelterwood systems are ‘evenaged
silvicultural systems, in which, in order to provide
a source of seed and/or protection for regeneration, the
old crop (the shelterwood) is removed in two or more
successive shelterwood cuttings, the first of which is
ordinarily the seed cutting (though it may be preceded
by a preparatory cutting) and the last is the final cutting,
any intervening cuttings being termed removal cuttings’
(Ford-Robertson 1983). Where there is adequate
regeneration the old crop may be removed in a single
cut (e.g., Malayan Uniform System). Preparatory felling
means removing trees near the end of a rotation so as to
open the canopy permanently and enlarge the crowns of
seed bearers, with a view to improving conditions for
seed production and natural regeneration. Here, no
adequate regeneration is on the ground. Seeding felling
is removing trees in a mature stand so as to effect
permanent opening of its canopy (if there was no
preparatory felling to do this) to provide suitable
conditions for regeneration from the seed of trees that
are retained. Removal felling is removing trees between
the seed cutting and the final cutting, so as gradually to
reduce the shelter and admit more light to aid the
regeneration crop and to secure further recruitment. This
type of felling is carried out over adequate regeneration.
There is almost 80 years of experience with the
regeneration of natural dipterocarp forests. Experience
on individual aspects of natural regeneration gained is
with modification applicable to even-aged stands of
dipterocarps. This does not mean regeneration systems
for even-aged stands can be derived from the knowledge
available now but it is possible to outline some general
directions.
One important aspect of the establishment of a new
generation by natural regeneration is, whether or not the
stands will fruit well before the rotation has ended. A
few observations have been made. Ng (1966) concluded
from his work on age of first flowering of dipterocarps
that many species begin to flower and bear good seed
before their 30th year. Tang (1978) found three trees of
Shorea leprosula planted in a taungya stand had fruited
at the age of 7 years. Similar early ages of flowering/
fruiting were reported by Lee (1980) for Shorea pinanga
(flowering 6 years after planting) and by Suziki and
Gadrinab (1988/1989) for S. stenoptera (fruiting 6 years
after planting). Ardikoesoema and Noerkamal (1955)
described a S. leprosula stand in Java that had fruited
aged 13 years producing a moderately dense seedling
crop. Appanah and Weinland (1996) evaluated the field
files of the dipterocarp plantations at the Forest Research
Institute Malaysia and fruiting was reported for Shorea