The Management of Teak Plantations
8/28/97
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RELAYED TEXT STARTS HERE:
Headline: The Management of Teak Plantations
Source:
Julio Cesar Centeno, PhD
Las Tapias, Edif. Carreto
Pent House Tel. +58-74-714576
PO Box 750 Fax +58-74-714576
Merida - Venezuela Email: JCenteno@ciens.ula.ve
http://www.ciens.ula.ve/~jcenteno/
Date: 8/28/97
THE MANAGEMENT OF TEAK PLANTATIONS
Julio C,sar Centeno
NOTE: A complete version of this article may be found in the
ITTO Tropical Forest Update, Volume 7, No. 2, 1997,
or at the following web page:
http://www.ciens.ula.ve/~jcenteno
Teak [Tectona grandis L] is a tree originally from an area encompassing
parts of India, Thailand, Myanmar and Laos. It seems to have been
introduced to Java, Indonesia, in the 14th century. There are references
to plantations established in India in the early 1800s, and in tropical
America about 100 years later.
Although it is not devoid of silvicultural and management difficulties,
it is a well-known timber species, which has performed well in
plantations not only in its Southeast Asian range of origin, but also in
other parts of Asia, as well as in Africa and Latin America.
The total area under teak plantations today is estimated at 3 million
hectares (1). Good growth and high quality is associated with deep,
flat, and well-drained alluvial soils, rich in calcium; a mean annual
temperature between 22 and 27 degrees centigrade; and an annual
precipitation from 1,500 to 2,500 millimeters, with a marked dry season
of 3 to 5 months with a maximum of 50 millimeters of rain.
Dry site conditions are usually associated with stunted growth. Very
moist conditions may lead to faster growth, but also to a thick sapwood
and poor overall quality, including lower average density, less
attractive color, poor texture, and loss of strength.
Growth Patterns
The rate of growth and the quality of teak from plantations are largely
dependent on the type and quality of the seeds; the physical and
chemical characteristics of the soil, including topography and drainage;
on environmental variables such as rainfall, temperature and humidity;
and on management techniques.
Although a significant variety of growth patterns have been recorded in
different part of the world, the best managed and most productive
plantations tend to fall within a well defined range [Figure 1].
Nevertheless, there are many cases of poorly established and managed
plantations, with rates of growth below the lower estimate indicated in
this figure.
Figure 1: Yield Potential of Teak Plantations
Teak trees grown in plantations on good soils may reach an average of 60
centimeters of diameter at breast height [DBH], and 30 meters in height
in about 50 years. In comparison, the largest standing teak tree,
located in the Baw Forest Reserve of Myanmar, measured 2.4 meters in
diameter and 46 meters high in April of 1996 (2).
Establishment Phase
Teak establishes best on terrain cleared of competing vegetation. An
important aspect of plant competition may be sought in the relatively
large need for aeration of the root system, and in the species
requirements for light and nutrients. Like pioneer species, teak is
unable to stand much competition from other plants, or from trees of the
same species.
A viable option for the production of high volumes of quality teakwood
is to establish pure plantations on well-prepared and well drained
soils, and to manage them to reach a good average height before
flowering sets in, making branching more profuse.
Spacing should promote rapid development of the saplings. The usual
1,200 to 1,600 plants per hectare is a good range, with closure of the
canopy commonly taking place between the third and fourth year,
suppressing the development of weeds.
A larger number of trees may be considered desirable to close the canopy
quickly, to decrease the problems caused by weeds and the size of
lateral branches, while forcing the live crowns high up along the stems
in a shorter time. An early first thinning would then become necessary
to prevent stunting, while keeping a large enough basic stock on which
to mold a good final crop.
Pure stands have been associated with the deterioration of the soil and
erosion. However, there is limited conclusive evidence in this regard,
except when teak is planted on steep slopes; where undergrowth has been
systematically cleared; or where excessive burning has taken place. The
management of pure stands where a protective understorey is maintained
after canopy closure, tends to avoid the deterioration of the soil,
particularly when the undergrowth contributes to the fixation of
nitrogen.
Pure teak plantations are often prone to attack by defoliators,
especially when planted on unsuitable soils, poor in nutrients. On the
best sites, where healthy growth is present, attack by defoliators is
less frequent and intense, and can be further reduced with the
maintenance of a suitable understorey.
Stand Dynamics
A series of options are available to influence the development of a
plantation, as well as the quality and quantity of the timber produced.
Among these options is the space made available to each tree, which
strongly influences its patterns of growth, and therefore the overall
yield of the plantation.
The initial spacing of planting, coupled with the number, timing, and
intensity of thinnings, largely determine the space made available to
individual trees as they develop. These are fundamental decisions, with
a profound effect on production.
Trees within a stand also interact and compete with each other, with
reactions controlled mainly by their genetic base, and by the space,
nutrients and light available to each. This generates a dynamic within
the stand, which can be influenced by management decisions to achieve
desired production objectives.
Within determined limits of thinning, where only small and temporary
canopy gaps are created, total production should not deviate
significantly from the carrying capacity of the site. If thinning is
practiced late, the stand is affected by stagnation, with the loss of
growth potential. If, on the other hand, the stand is thinned too early
or too strongly, the trees tend to produce more side branches and
epicormic shoots. This also implies a loss of growth potential, since
the purpose is to produce as much timber in the main stem as possible,
preferably free of knots and defects.
Epicormic shoots may also be related to the genetic imprint of the
seeds. Erosion is a further threat when thinning is too strong.
Often the age at which the first thinning is practiced is determined by
the dominant height, which in turn is determined by site quality.
Dominant height is the average height of the 100 largest diameter trees
per hectare. It may also be estimated from the average height of the
five largest diameter trees in permanent sample plots, when these are of
0.05 hectares in size.
As a general rule, teak should be planted only on the best site classes,
with the first thinning taking place when the dominant height reaches 9
to 9.5 meters, and the second when the dominant height reaches 17 to 18
meters.
Each site has a certain carrying capacity, measured in terms of basal
area [the average cross-sectional area of all trees per unit of stand
surface]. The dominant height and the cumulative basal area are
parameters normally not affected by either the initial stocking nor by
thinning regimes. The thinning regime may thus be designed to
concentrate the basal area carrying potential of the site in a minimum
number of trees.
A guiding rule is to allow the mean basal area to build up to between 20
and 22 square meters per hectare after the second thinning, and then
thin the stand again to bring the mean basal area proportionately down
to between 13 and 15 M2 per hectare.
The combination of reliable information on dominant height and
cumulative basal area provides one of the best approaches to the
successful management of teak plantation in tropical environments.
Thinning and Pruning
Thinning and pruning operations are closely inter-related, with a strong
influence on the quality of the wood and on production performance.
Thinning regimes are dictated by the development of the trees in height
and basal area. Theoretically, the amount of all wood formed per hectare
will be more or less the same for stands of the same provenance, age and
site quality, but varying in numbers of trees, as long as the canopy
remains closed. How much wood goes into the branches of the crown, and
how much goes into the valuable part of the stem, depends largely on the
thinning schedule.
A common strategy to grow long boles, clear of knots, is to keep the
stand quite closed and high in number of trees during the first years of
development, when rapid height growth occurs. This is meant to keep
crowns small, and consequently limit the size of the branches.
Knot free timber is desired to improve the quality and appearance of
high-grade construction material, furniture, decorative veneer and
plywood, among other uses. It is also desirable to improve the working
properties of the timber, to facilitate peeling, finishing, and
seasoning, and for the uniformity of strength.
The management strategy can be designed to encourage the formation of
clear boles, by pruning the trees that will yield commercial timber,
while keeping the stand low in the number of stems. The trees then must
have larger individual crowns to keep the canopy closed, and the wood
volume produced will be concentrated on lower numbers of trees, which
thus will be thicker than in stands with higher numbers.
Even within a tree species, there may exist various provenances with
genetic predisposition for small or broad crowns. The thinning schedule
has thus to be adapted to the provenance used, and improved through
experience and experimentation.
The removal of branches up to a desired height is done first near the
time of canopy closure. Pruning also serves to reduce the chances of
ground fires reaching the crowns, and to facilitate access to the stand.
It is a costly operation, which should be perceived as an investment to
improve the quality of the final product. As much self-pruning as
possible should be provoked through stand architecture. Since both the
demand and the price for high quality tropical timber tend to increase,
pruning becomes an attractive silvicultural operation and a fruitful
investment.
For cost effectiveness, pruning should be done selectively, coordinated
with the intended method of thinning, clearing 2 to 3 meters of stem at
a time.
Nevertheless, teak has the propensity to produce adventitious branches
and epicormic shoots next to the scars caused by pruning. To prevent
their development, pruning should be carried out just after the period
when most new leaves are produced. To minimize damage, it is better to
sever the branch about 30 cm from its connection with the stem, before
cutting the stub flush with the trunk of the tree, using a pruning saw.
This prevents the branch from breaking when the saw cut is nearly
complete, tearing a strip of bark from the stem as it falls.
A balance is necessary between the need to produce knot free timber, the
stem length pruned at a time, and the need to prevent a slowing down of
growth due to an excessive reduction of the crown.
Rotation
Based on a weighed assessment of economic and silvicultural
considerations, a rotation of 25 years to 40 years may at present be
considered as the optimum cycle to achieve a viable balance between
financial returns and the production of market quality timber. During
this rotation period, thinning operations will provide returns at
intermediate stages, easing the economic burden related to the long-term
nature of the operation, and making the investment financially
attractive.
In Asia, teak trees are often allowed to develop for 60 years or more
before harvesting. At such ages, the mean annual increments may vary
from 3 to 10 cubic meters per hectare per year. Most plantations in
tropical America are managed with far shorter rotations, usually from 20
to 30 years. The mean annual increment at such ages may vary from 10 to
20 cubic meters per hectare. This does not mean teak grows better or
faster in America. Were these plantations allowed to develop for 60 or
80 years, they would register similar mean annual increments as those in
Asia for the same age.
References
1. Own estimate based on a) FAO Forestry Paper 128: Tropical Forest
Plantation Resources, 1995. b) TEAKNET Second Regional Seminar on Teak,
Yangon, Myanmar, 1995. c) Pandey: Assessment of Tropical Forest
Plantation Resource, 1992. d) Own collection of statistics between 1990
and 1996 for tropical America.
2. Myanmar Forest Service: Myanmar's Mighty Teak Tree, 1996.
______________________________________________
Julio Cesar Centeno, PhD
Las Tapias, Edif. Carreto
Pent House Tel. +58-74-714576
PO Box 750 Fax +58-74-714576
Merida - Venezuela Email: JCenteno@ciens.ula.ve
http://www.ciens.ula.ve/~jcenteno/
_______________________________________________