The Management of Teak Plantation

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. Some scientists consider the island of Java as part of the natural range for the species. It 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.

Teak has been cultivated in the tropics for centuries. 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 may be fairly said that it is a well-known timber species, relatively benign and successful in plantation environments in the tropics.

The total area under teak plantations today is estimated at 3 million hectares. 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. 

Figure 1: Yield Potential of Teak Plantations

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.

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 [Ref.Myanmar Forest Service: Myanmar's Mighty Teak Tree, 1996].

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 requirements for light and nutrients. The light requirements of teak are those of a pioneer species, unable to stand much competition from other plant species, 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 be relatively wide, to 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 with 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 per ha 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.

The basal area of a stand is the average cross-sectional area of all trees per unit of stand surface, normally measured at breast height. It is also useful to guide thinning operations, particularly during the latter stages of development of the plantation. Each site has a certain carrying capacity, measured in terms of basal area. The dominant height and the cumulative basal area are parameters normally not affected by the initial stocking or 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 the branches relatively small and thin. 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 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. It is therefore justifiable only when the extra revenues involved out-balance the costs. As much self-pruning as possible should be provoked through stand architecture. Nonetheless, since both the demand and the price for high quality tropical timber tends 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, to clear 2 to 3 meters of stem at a time. To prevent the development of epicormic shoots, the operation should be carried out just after the period when most new leaves are produced. To minimize damage, it is better to sever the main 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.

Nevertheless, teak has the propensity to produce adventitious branches and epicormic shoots next to the scars caused by pruning. 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.

Julio César Centeno, PhD 

Apartado 750 

Mérida-VENEZUELA 

Tel / Fax: +58 74 714576
Email: Jcenteno@ciens.ula.ve
URL: www.ciens.ula.ve/~jcenteno

Original Article Here