A review of dipterocarps - Center for International Forestry Research

Plantations 154
are: Dipterocarpus grandiflorus, D. warburgii,
Parashorea plicata, Shorea almon, S. guiso, S.
negrosensis, S. polysperma and S. squamata. Newman et
al. (1996) compiled a manual of dipterocarps for the
Philippines.
Silvics
Silvics deals with the life history and general
characteristics of forest trees and stands particularly
refering to locality factors as a basis for the practice of
silviculture.
For tree species of the high forests (a closed forest of
tall trees), tolerance is their ability to grow satisfactorily
in the shade of and in competition with other trees. If
intolerant of shade, a species is termed a ‘light demander’,
if tolerant, a ‘shade bearer’. Discussions on how much
light should be given for good growth and how much
shade should be retained started early. Sanger-Davies
(1931/1932) considered most of the commercial
dipterocarp species as light demanders which should be
given full overhead light and full space for maximum
development. While larger plants need full light for good
growth, young seedlings need a shelter either from
existing belukar or from planted nurse crops. Indeed,
planting of dipterocarps under a nurse crop (e.g.,
Paraserianthes falcataria) was successful in the
experimental plantations in Indonesia (e.g., Masano et
al. 1987) and Malaysia (Barnard 1954) and elsewhere in
the region (e.g., Doan 1985). All shading experiments
showed without doubt that optimal growth of dipterocarp
seedlings is only achieved under partially shaded
conditions (e.g., Nicholson 1960, Mori 1980, Sasaki and
Mori 1981 and others).
There is a wide range of shade tolerance among older
seedlings/saplings of dipterocarp species which follows
the known pattern of higher shade tolerance for late
succession species and higher light demands for earlier
succession species (e.g., Strugnell 1936a). Qureshi (1963)
classified about 100 tree species (including. Shorea
robusta) as tolerant, moderately and intolerant of shade
in comparison to Acacia arabica which is intolerant of
shade at every developmental stage. In Peninsular
Malaysia, field experiments on light requirements were
established early in conjunction with Regeneration
Improvement Systems and a discussion on canopy
manipulations over young regeneration ensued (e.g.,
Sanger-Davies 1931/1932, Watson 1931/1932b, Walton
1936b). However, this type of experiment was abandoned
when Regeneration Improvement Systems ceased in
Malaya in the 1930s. JICA (1993, 1994) reported an
underplanting trial where dipterocarps (Shorea
leprosula, S. parvifolia, Dryobalanops aromatica and
others) have been underplanted in Acacia mangium
stands with different size gaps. The performance was best
where two rows had been removed (9 m opening).
Controlled (artificial) experiments are needed for base
line information on the light requirements of species to
be complemented by field trials where shade from natural
vegetation is manipulated. More details on the light
physiology of seedlings can be found in Chapter 3.
Mycorrhizal symbiosis with dipterocarps has
received great attention in recent years. Since this field
is dealt with in detail in Chapter 6, only some practical
aspects are discussed here. The importance of
mycorrhizal symbiosis for the survival and growth of
trees is not in question. Most of the investigations deal
with the identification of mycorrhizal fungi and their
strains/forms (e.g., Louis 1988) and Lee and Lim (1989)
have reported mycorrhizal infection of dipterocarp
seedlings in logged and undisturbed forests. Host
specificity of mycorrhizal fungi was reported by Smits
(1982) and it is concluded that the chance of a seedling
finding the right fungus is better the closer the seedling
germinates and grows to the mother tree. He explains
the formation of eco-unit patterns as linked to such a
preference. Whether host specificity is wide spread
among dipterocarps remains to be investigated.
Alexander et al. (1992) found that the root contact of
seedlings with mature trees is important for the infection
with mycorrhizae which would have a bearing on the
design of regeneration systems. The retention of mature
trees seems to be important for this reason. Turner et al.
(1993) investigated the effect of fertilser application on
dipterocarp seedling growth and mycorrhizal infection.
The application involved 10 g m -2 N, P 2 O 5 and K 2 O to
Shorea macroptera seedlings grown in pots of forest
soil (nursery condition). The results showed that
mycorrhizal infection was significantly higher for
fertilised seedlings. Oldeman (1990) draws attention to
the fact that mycorrhizal symbiosis occurs particularly
on poorer, acid soils and suspects that by changing the
chemical status of the soil through fertilisation,
mycorrhizal functioning might be impaired. Santoso
(1987, 1989) showed that there is an increase in shoot/
ratio, dry weight of leaves, roots, stem diameter, as well
as absorption potential for nutrients among several