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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Plantations 167<br />
have resulted from, e.g., Regeneration Improvement<br />
Systems or from Uni<strong>for</strong>m Shelterwood Systems, as they<br />
were, <strong>for</strong> example, applied in Malaysia. Wyatt-Smith<br />
(1963b) gives a thorough <strong>review</strong> <strong>of</strong> the thinning<br />
experience up to that time. His recommendations <strong>for</strong><br />
thinning more or less regular crops were:<br />
• removal <strong>of</strong> climbers <strong>of</strong> above 2.5 cm diameter, although<br />
the limit can be lower if smaller climbers prove<br />
to be damaging the crop trees,<br />
• removal <strong>of</strong> all weed trees; also those that are going to<br />
overtop the PCT until the the next intervention,<br />
• removal <strong>of</strong> all mal<strong>for</strong>med stems <strong>of</strong> commercial species<br />
provided a stem <strong>of</strong> better <strong>for</strong>m is adjacent,<br />
• removal <strong>of</strong> all wolf trees,<br />
• removal <strong>of</strong> co-dominants <strong>of</strong> inferior timber value,<br />
• selective thinning <strong>of</strong> co-dominants <strong>of</strong> equivalent<br />
silvicultural and timber value that compete strongly,<br />
and<br />
• thinning to a maximum basal area <strong>of</strong> about 1/2 to 3/4<br />
<strong>of</strong> the expected carrying capacity <strong>of</strong> the site.<br />
In the context <strong>of</strong> regeneration operations within the<br />
Regeneration Improvement Systems Durant (1940) was<br />
confronted with the criticism that opening the canopy<br />
would lead to luxuriant ‘secondary growth’ (what we<br />
would call today secondary <strong>for</strong>est) consisting mainly <strong>of</strong><br />
Randia scortechenii, Pasania sp., Barringtonia sp.,<br />
Girroniera nervosa, Trema ambionensis, Macaranga<br />
spp., Endospermum malaccense and various fast-growing<br />
trees <strong>of</strong> other families. It was feared that the young<br />
<strong>dipterocarps</strong> might be suppressed by these species and<br />
frequent and expensive cleanings needed. Three<br />
experimental plots were set up. Two plots were<br />
established in stands where the canopy over young<br />
regeneration had been removed by regeneration<br />
improvement fellings and one plot was laid out in an area<br />
where the canopy over young regeneration had almost<br />
completely been removed by a heavy storm. The<br />
treatments in the first plot were: (i) untouched control,<br />
(ii) cleaning (cutting back all growth other than Shorea<br />
spp.), and (iii) cleaning and respacing (‘thinning’ <strong>of</strong> the<br />
Shorea spp. to an average distance <strong>of</strong> 1.83 m leaf to leaf).<br />
The treatments in the second plot were: (i) untouched<br />
control, (ii) cleaning (cutting back everything except<br />
saplings <strong>of</strong> the desirable species), and (iii) mainly climber<br />
cutting with minimal cutting <strong>of</strong> undergrowth. In the third<br />
plot only a cleaning in favour <strong>of</strong> saplings and small poles<br />
was carried out. The objective <strong>of</strong> the first two plots was<br />
to investigate the effect <strong>of</strong> the secondary <strong>for</strong>est vegetation<br />
on survival and diameter growth <strong>of</strong> sapling-size natural<br />
regeneration <strong>of</strong> Shorea spp. The third plot tested whether<br />
larger regeneration (large saplings, small poles) was out<br />
<strong>of</strong> danger from its competitors. After establishment, the<br />
plots were left unattended <strong>for</strong> four years and then<br />
enumerated again.<br />
From Durant’s experiment, inferences were made<br />
concerning the regeneration <strong>of</strong> S. leprosula:<br />
• However severe the opening <strong>of</strong> the canopy, provided<br />
adequate seedling regeneration is present, S. leprosula<br />
can tolerate competition with other vegetation up to<br />
the sixth year.<br />
• Cleaning and thinning after the second year will secure<br />
an even distribution <strong>of</strong> stocking and will increase<br />
the growth rates. Complete omission <strong>of</strong> tending up to<br />
the sixth year is not fatal (which is in agreement with<br />
other authors e.g., Walton 1933, 1936a, Wyatt-Smith<br />
1949b, 1958, 1963b).<br />
• Serious competition from secondary <strong>for</strong>est species<br />
is probably due to a comparatively few species, and, if<br />
these can only be recognised and eliminated, a considerable<br />
reduction <strong>of</strong> cleaning costs should be possible.<br />
(The species recognised as responsible <strong>for</strong> suppression<br />
were Endospermum malaccense,<br />
Elaeocarpus stipularis, Macaranga spp., Paropsia<br />
varedi<strong>for</strong>mis and Quercus lucida).<br />
• With sufficient initial opening <strong>of</strong> the canopy, good<br />
stocking <strong>of</strong> Shorea leprosula can be expected to survive<br />
up to the 14th year. At this stage the crop reaches<br />
pole size, and adequate assistance can be given very<br />
cheaply by the poison-girdling <strong>of</strong> competitors around<br />
individual trees.<br />
The conclusions are important <strong>for</strong> the tending <strong>of</strong><br />
young naturally regenerated and more or less even aged<br />
stands originating either from natural stands or from<br />
plantation stands under the Shelterwood System. The<br />
findings <strong>of</strong> Durant (1940) can, however, not be applied<br />
without some restrictions to young plantations <strong>of</strong><br />
<strong>dipterocarps</strong>. The initial number <strong>of</strong> stems in plantations<br />
is usually so low that omission <strong>of</strong> early tendings<br />
(weedings, cleanings) will probably entail high losses<br />
endangering stand establishment.<br />
Strugnell (1936b) tried three treatments (only<br />
dominant trees retained; dominant and dominated trees<br />
retained; dominant, dominated and suppressed trees<br />
retained) in a young natural pole stand <strong>of</strong> Shorea leprosula<br />
and S. parvifolia. He found that the basal area <strong>of</strong> the 50<br />
largest trees/acre was highest <strong>for</strong> the medium