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