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