A review of dipterocarps - Center for International Forestry Research

Management of Natural Forests
about 4000 viable seeds in a good year (Champion and
Pant 1931), and the seeds germinate within a few days.
Sal seedlings are shade tolerant and establish better under
the crowns of other trees. Seedlings are able to coppice
and also develop a deep taproot. They are thereby able
to withstand ground fire and cattle browsing.
Other dipterocarps of this formation are believed to
regenerate like sal. All flower during the dry season, and
fruit with the onset of rains. A light ground fire before
seed-fall assists seedling establishment. Among some
species, seedling establishment seems rare in nature
(Blanford 1915), and regeneration is principally by
coppicing. Mature trees are known to coppice readily
following injury.
Seasonal Evergreen Dipterocarp Forests
The dipterocarps of this formation belong to the mature
phase of the forest. An exception is Anisoptera thurifera
in Papua New Guinea which can establish in cultivated
areas (Johns 1987). The regeneration of the dipterocarps
in these forests resembles that of the sal in many ways,
except for the role of fire. Dipterocarp populations
flower almost annually, but flowering is only heavy at
intervals of 3-4 years (Chengappa 1934). The fruits are
heavily predated by insects, birds and mammals, and
seedling survival is poor. In some genera like
Dipterocarpus, many years may pass without a single
seedling becoming established. They also lose their
coppicing ability after the sapling stage. Overall, the low
seedling survival and the early loss of coppicing ability
makes it difficult to regenerate these forests after
exploitation.
Aseasonal Evergreen Dipterocarp Forests
The regeneration of dipterocarps in these forests has
been relatively well studied. The dipterocarps have a
unique flowering characteristic - they flower at supraannual
intervals of 2 to 7 years, and the event may be
widespread covering sometimes the whole region
(Ridley 1901, Foxworthy 1932, Ashton 1969, reviewed
by Appanah 1985). Whole forests may burst into
flowering synchronously. It is not limited only to the
dipterocarps though, and many other canopy and
emergent species also participate in the flowering. Some
localised flowerings also occur almost every year.
During heavy flowering years, each mature
dipterocarp may set up to 4 million flowers, and this
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results in as many as 100,000 mature fruits. Much is
lost to insects, birds and mammals. The ripe fruit fall
somewhat synchronously, however, the winged fruits are
not dispersed far from the mother trees. The dipterocarp
seeds lack dormancy, and germinate soon after falling.
Once established, seedling populations decline slowly
only as a result of inadequate light conditions and
aperiodic droughts. Growth is rapid if they are exposed
to direct light (Wyatt-Smith 1963, Fox 1973). Among
the dipterocarps, light demanders and shade tolerant
species can be differentiated. Both grow rapidly where
there is higher light intensity, but the latter species can
survive longer under poorer light conditions, and in
general they are the slower-growing heavy hardwoods.
In contrast to dipterocarps in the other two formations,
coppicing ability of the species in the everwet forests
is limited, and ceases beyond the pole stage. The
population structure is not the typical reverse-J shape,
with the density of sapling-and pole-size dipterocarps
generally low in mixed dipterocarp forests. However,
this appears to be not so in some of the dipterocarprich
forests in the Philippines.
Silvicultural Systems
A number of silvicultural systems have been developed
for the long-term management of tropical forests, many
with dipterocarps as the main crop. The silvicultural
systems go by a bewildering number of technical names,
but they can be broadly divided into Shelterwood
(monocyclic) Systems and Selection (polycyclic)
Systems. The situation for dipterocarps forests have
been reviewed variably (e.g. Wyatt-Smith 1963, 1987,
FAO 1989, Stebbing 1926, Chengappa 1944, Nair 1991,
Weidelt and Banaag 1982, and others).
Simply stated, the Shelterwood System attempts to
produce a uniform crop of trees from young
regeneration through both heavy harvesting and broad
silvicultural treatments. A new even-aged crop is
established by applying preparatory and establishment
cuttings to natural regeneration (i.e. seedlings and
saplings) of the desired trees. At an appropriate time
the remaining overstorey is removed.
The Selection System aims to keep an all-aged stand
through timber cuttings at shorter intervals. Many light
cuttings are made. Seedlings will become established
in the small gaps. Under this system, two or more less