A review of dipterocarps - Center for International Forestry Research

Management of Natural Forests
intensive harvests are possible during one rotation, while
in the Shelterwood System all marketable stems are
removed at one cutting.
A variety of silvicultural systems have been tried out
on dipterocarp forests, depending on markets,
technological changes, landuse patterns, harvesting,
regeneration, labour costs, etc. These have met with
varying success. The systems in operation in India,
Malaysia, Philippines and Indonesia described as forest
management practices are well documented in these
countries.
India
The seasonal evergreen and dry evergreen forests have
been managed under the Selection System. Here it can
be summarised as selective felling of exploitable trees
from an area at periodic intervals, under the following
circumstances: i) in mixed forests where utilisable
species are few; ii) in areas that are difficult to access;
and iii) in hilly terrain where heavy logging is
environmentally bad.
Trees of specific girth are removed at 15 to 45 year
cutting cycles, calculated from growth rates. Some
safeguards are introduced such as: a 20 m minimum
distance between trees earmarked for felling; climber
cutting to reduce logging damage; protection buffers for
riversides; and only harvesting dying and dead trees in
steep areas. Treatment is carried out to assist natural
regeneration, and planting is prescribed for understocked
areas. Many of the prescriptions are not met for
several reasons: plantings are inadequate and damage to
residuals excessive (FAO 1984). Over time, felling
cycles have been reduced, girth limits lowered, and more
species exploited.
Shelterwood Systems
Shelterwood Systems were introduced when it became
necessary to harvest more intensively some valuable
forests, and regeneration was not assured under the
selection system. The variants usually applied here are
the Indian Irregular Shelterwood System, Uniform
System and the Coppice System.
1. Indian Irregular Shelterwood System
Both seasonal evergreen and sal forests are managed
under this system. First, all trees above exploitable
diameter are removed. If advanced growth is lacking,
mother trees are kept. Next, the underwood and
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overwood are removed periodically until regeneration
becomes established. Finally, the remaining underwood
and overwood is removed, except those forming future
crops. All these are done over a rotation of 120 years. In
addition, girdling, thinning, weeding, climber cutting and
artificial planting are carried out as needed.
Lack of regeneration, especially for sal forests,
appears to undermine the Irregular Shelterwood System
(FAO 1989). Plantings have been tried at cost. This has
not kept to schedule, and there is a temptation to reduce
rotation length and exploitable girth limits.
2. Uniform System
In high value sal forests, the Uniform System has been
tried. All overwood is removed at one clearfelling, and
regeneration is allowed to grow up. No regeneration
fellings are conducted, however, and so the system has
to rely on pre-existing seedlings. The rotations are
between 120 to 180 years for sal. But demand for timber
is high and rotations have been shortened.
When natural regeneration is abundant, the overwood
is cut completely. Groups of poles are sometimes kept
as future crop trees if regeneration is poor. Where
regeneration has not established, suppressed trees are
retained to control weed growth. Steep slopes and eroded
areas are not heavily felled. Cutting and thinning are
prescribed for improving regeneration. The system
should work if adequate natural regeneration can be
secured. In the event it is poor, artificial regeneration
has been resorted to.
3. Coppice Systems
A few variants of the Coppice Systems have been
introduced for sal forests. The systems depend on shoots
emerging from the cut stumps. Coppicing vigour declines
with age and so short rotations are necessary. It is mainly
suitable for firewood and small timber production. To
produce fuelwood, a rotation of 30-40 years is used.
Felling is done before the growing season, the area is
protected from grazing and fire, and cleaning is done to
remove excess coppice shoots and climbers. Over time,
with decline in coppicing vigour, stump mortality
increases. Seedling regeneration helps to compensate
this loss, but seedlings are scarce because of grazing
pressure. This has led to stand degradation. Variations to
the system involve retention of seed trees for producing
seedlings (see Tiwari 1968). Overall, the system has
succeeded where biotic pressure is kept low.