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
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
Plantations 169<br />
leprosula, S. macrophylla and Dryobalanops aromatica<br />
stands at about 20 years age. Additionally, plantation<br />
stands <strong>of</strong> some other species (e.g., Dryobalanops<br />
oblongifolia, Shorea macroptera) have established<br />
regeneration. However, the exact stand age at first<br />
flowering has not been recorded.<br />
Little in<strong>for</strong>mation is available concerning<br />
preparatory operations. Chong (1970) reported the effect<br />
<strong>of</strong> Eugeissona triste (a stemless palm) control on<br />
regeneration <strong>of</strong> Shorea curtisii. The experiments<br />
showed that a pre-felling treatment with a light girdling<br />
and Eugeissona triste control undertaken after a heavy<br />
seed fall prior to felling had a beneficial effect. The<br />
operation not only increased the vigour <strong>of</strong> the established<br />
regeneration but also created conditions on the <strong>for</strong>est<br />
floor conducive to recruitment <strong>of</strong> new individuals. Raich<br />
and Gong (1990) found that seed germination<br />
demonstrates clear patterns <strong>of</strong> shade tolerance or<br />
intolerance identical to those long recognised <strong>for</strong> tree<br />
seedlings. Among the species tested were Dipterocarpus<br />
grandiflorus, Shorea multiflora and Vatica nitens. They<br />
germinated in the understorey as well as in the gaps<br />
(typically 20-30 m in diameter) but failed to germinate<br />
in larger clearings. So, if preparatory canopy openings<br />
are prepared, these openings should not exceed normal<br />
gap size.<br />
Preparatory fellings have never played an important<br />
role. Treatment <strong>of</strong> seed trees in the natural <strong>for</strong>ests to<br />
improve their crowns is unneccessary because being<br />
emergents they have already fully developed crowns.<br />
More in<strong>for</strong>mation is available on the manipulation <strong>of</strong> the<br />
old crop over existing regeneration (regeneration fellings<br />
and final fellings). Although strictly applicable only to<br />
natural <strong>for</strong>est conditions, the basic findings should also<br />
be valid <strong>for</strong> plantations. Based on closely controlled<br />
experiments in the Wet Evergreen Forests <strong>of</strong> Sri Lanka,<br />
Holmes (1945) found that canopy conditions under<br />
seeding fellings most conducive to regeneration seem<br />
to be gaps <strong>of</strong> 20-30 m diameter evenly distributed and<br />
separated from one another by not more than one row <strong>of</strong><br />
dominant trees. While raising the canopy gradually<br />
upwards, an ultimate canopy density <strong>of</strong> about 0.5 will be<br />
achieved. Zoysa and Ashton (1991) found that the<br />
germination <strong>of</strong> Shorea trapezifolia seeds planted on<br />
<strong>for</strong>est top soil with litter was little affected by partial<br />
shade or exposure to full sun. Watson (1931/1932c)<br />
discusses ‘preparatory’ fellings (strictly speaking they<br />
were regeneration fellings) <strong>for</strong> fostering natural<br />
regeneration within plantations. He states that seedlings<br />
<strong>of</strong> commercial species would establish better after<br />
opening the <strong>for</strong>est canopy, provided care is taken to<br />
prevent intrusion <strong>of</strong> weed species. He recommends<br />
removal <strong>of</strong> the lower <strong>for</strong>est canopy layers and cleaning<br />
<strong>of</strong> the undergrowth. But no fellings <strong>of</strong> this kind should<br />
be done in the absence <strong>of</strong> natural regeneration. Based on<br />
experiments <strong>of</strong> girdling understorey and upper storey<br />
trees, it was concluded that improvement systems should<br />
ensure adequate regeneration while retaining the canopy<br />
in such a condition that the lower storey is shaded<br />
preventing growth <strong>of</strong> competing vegetation (Walton<br />
1933, 1936a, b). Only after regeneration is abundant<br />
should any drastic opening <strong>of</strong> the canopy be undertaken.<br />
The vigorous response <strong>of</strong> seedling regeneration <strong>of</strong><br />
Shorea spp. to full light indicates that treatment should<br />
aim at removing the canopy as rapidly and completely as<br />
is considered safe. The extent <strong>of</strong> canopy opening,<br />
however, should depend on the light demand/shade<br />
tolerance <strong>of</strong> the species. Strugnell (1936a) investigated<br />
the effect <strong>of</strong> suppression on young regeneration <strong>of</strong><br />
Shorea leprosula, S. parvifolia and Neobalanocarpus<br />
heimii. Removal fellings should not be delayed <strong>for</strong> too<br />
long in light-demanding species as mortality will be high<br />
and growth responses weak. Shade tolerant species may,<br />
however, react vigorously even after a long time <strong>of</strong><br />
suppression. In some species sudden exposure on canopy<br />
opening might lead to shoot borer attack as in<br />
Neobalanocarpus heimii (Durant 1939). Qureshi et al.<br />
(1968) emphasise that, be<strong>for</strong>e commencing tending<br />
operations on the regeneration, the canopy density has<br />
to be reduced to ensure sufficient light <strong>for</strong> the young<br />
plants. This was tested on natural regeneration <strong>of</strong> Shorea<br />
robusta under a planted parent stand. In mixed stands<br />
smaller gap sizes will favour shade tolerant species and<br />
larger gap sizes light demanding species. This is an<br />
important consideration if mixed stands <strong>of</strong> shade tolerant<br />
and light demanding species are to be regenerated (e.g.,<br />
Raich and Gong 1990).<br />
The design <strong>of</strong> the regeneration system <strong>for</strong><br />
dipterocarp plantations depends, apart from the<br />
production goal, on several other factors, e.g., the species<br />
involved, the stand condition, the regeneration behaviour<br />
and site factors. A uni<strong>for</strong>m shelterwood system could,<br />
<strong>for</strong> example, be applied to Dryobalanops aromatica<br />
stands (Zuhaidi and Weinland 1993). They usually carry<br />
a fairly dense regeneration that is evenly distributed over<br />
the stand area. The canopy <strong>of</strong> the old crop is distinctly