A review of dipterocarps - Center for International Forestry Research

Plantations 165
young dipterocarp plants can withstand light shade it is
not necessary to remove all non-crop vegetation. It would,
therefore, be more appropriate to develop more selective
procedures with less competitive weeds being left.
Barnard (1954) gives the following general
recommendations for weeding operations:
• plants must be kept free of climbers;
• freeing from climbers must be done before the plants
have been overgrown;
• uprooting of weeds is preferable to slashing to prevent
vigorous regrowth;
• grasses and young plants compete for moisture and
nutrients and should be periodically removed by cleanweeding
in a circle around the plant; and
• weeding should not be done with a hoe, to avoid damage
to the plants.
More investigations are needed on selective weed
control, including the development of risk categories for
so-called weed trees and methods of suppression or
elimination. Useful descriptions of weed vegetation in
the Malaysian context are found in the rubber planter’s
manual (Haines 1940). Such a manual became necessary,
when the so-called ‘forestry’ cultivation was introduced
in rubber plantation management. The basic idea was to
retain an undergrowth of non-competitive vegetation so
as to prevent erosion and maintain favourable soil
chemical and physical properties. Naturally, only
harmless weeds could be allowed to grow in the
plantations. This made it necessary to categorise the
vegetation according to noxiousness and to define the
treatments required. Weeds particularly noxious to
young plants have been noted, e.g., Wyatt-Smith (1949b),
Seth and Dabral (1961), Palit (1981). Wyatt-Smith
(1963b) listed ‘weed’ trees that had to be poisoned
irrespective of whether competing with ‘economic’
species or not. The control of specific types of weeds
has been described, e.g., Strugnell (1934), Mitchell
(1959) for Imperata cylindrica, Kelavkar (1968) for
Lantana camara, and Palit (1981) and Bogidarmanti
(1989) for Mikania spp. Liew (1973) tested methods
to eradicate climbing bamboo (Dirochloa spp.) in Sabah
and was successful with merely cutting the bamboo near
the soil surface. Chemical weeding was tested by Palit
(1981) in Shorea robusta plantations against Mikania
scandens. Seth and Dabral (1961) tested the efficiency
of 5 herbicides based on 2,4-D or 2,4,5-T in moist
deciduous Shorea robusta forests against trees and
coppice of Mallotus philippinensis, Ehretia laevis,
Ougeinia oojeinensis, Miliusa velutina, Buchanania
lanzan, Aegle marmelos. M. philippinensis proved to
be resistant. Chong (1970) carried out a trial on chemical
control of the stemless palm Eugeissona triste in Shorea
curtisii forests. In regions with distinct seasonality,
timing of the weeding operations is important. Bhatnagar
(1959) related the timing of the weeding operations to
the annual height increment peaks of Shorea robusta
seedlings. He recommended carrying out weedings
during or somewhat in advance of these periods, so as to
help to relieve the intense competition between the
Shorea robusta seedlings and the weeds. In Shorea
robusta forests the so-called rain-weeding is carried out,
i.e., weeding during the rainy season (e.g., Rowntree
1940, Sarkar 1941). For good growth of the young
planted dipterocarps a good exposure to light is essential.
In line plantings (including enrichment planting)
overhead shade must be continuously absent from the
planting lines. Agpaoa et al. (1976) give a comprehensive
description of the procedure of enrichment planting and
the corresponding tending operations. In underplanting
under a nurse crop the overhead shade must be removed
within a few years (e.g., Sanger-Davies 1931/1932,
Ardikoesoema and Noerkamal 1955, Wyatt-Smith
1963b Agpaoa et al. 1976). Small undesirable trees (up
to about 5 cm diameter) can easily be removed with a
bush knife or axe. Larger trees, however, are frequently
girdled or poison-girdled using arboricides. Arboricide
use is described e.g., Sanger-Davies (1919), Barnard
(1950, 1952), Beveridge (1957), Nicholson (1958),
Roonwal et al. (1960), Wyatt-Smith (1960, 1961a,
1963c), Wong (1966), Liew (1971), Agpaoa et al.
(1976), Chai (1978), Chew (1982) and Manokaran et
al. (1989). Well known arboricides are 2,4,5-T, Garlon
4E, Tordon 22K, Velpar-L and sodium arsenite. Most
of the tests were done with 2,4,5-T and sodium arsenite.
Thinnings
Thinning is ‘a felling made in an immature crop or stand
in order primarily to accelerate diameter increment but
also, by suitable selection, to improve the average form
of the trees that remain, without - at least according to
classical concepts - permanently breaking the canopy’
(Ford-Robertson 1983). A thinning regime is
characterised by type, grade or weight and frequency. The
type of thinning can be a thinning from above, where
particularly the most promising, not necessarily the
dominant, stems are favoured and where those trees, from
any canopy class that interfere with the promising ones,