Large tree with a straight stem; bark pale grey, with shallow longitudinal fissures. Leaves opposite, very large, up to 60 cm long, underside densely hairy. Flowers white in erect terminal panicles. Fruit covered in felty hairs, and enclosed by the inflated calyx.
A deciduous tree, capable on good sites of reaching a very large size. It is a pronounced light-demander and will not tolerate suppression at any stage of its growth. Its best growth is on deep well-drained loamy to sandy loam soils; It will grow on harder and shallower soils, but then its rate of growth is reduced. It is not sensitive to pH, and grows very well on soils derived from limestone, as long as they are deep enough. It does not tolerate badly drained soils.
Tectona grandis is better than some species at surviving where there is grass and weed growth, but good weeding is needed to obtain satisfactory rates of growth. Accumulation of moist weeds round young seedlings often causes them to rot. It is very resistant to fire, and even young plants when burnt generally shoot from the root. This burning back and shooting may continue for several years, while the root gradually increases in size, and eventually produces a shoot which escapes the fire. Older trees are little damaged by grass fIres unless there is an accumulation of dry branches or other inflammable material near the base of the stem. The seedlings are killed by frost, and T. grandis should not be planted in frosty areas. It is not readily browsed, though wild pigs may do damage by rooting up the seedlings. It coppices very well even when the trees are of large size.
In plantations T. grandis suppresses nearly all undergrowth, leaving a bare floor with little but fallen leaves. This means that there is little ground protection, and T. grandis should not be planted in pure plantations on sloping erodible sites.
Tectona grandis is not indigenous to Nepal or northern India, but is found in the Indian peninsula, Burma, Thailand, Laos and Indonesia, though there are doubts whether it is truly indigenous in Indonesia. It has been very widely planted in tropical countries for its timber.
In India the fruits ripen between November and January and gradually fall to the ground during the hot season. They can easily be collected from the ground since such seed is just as good, if not better, than seed collected from the tree. At present few stands in Nepal have reached the seed production stage, and most seed will need to be imported. What is commonly referred to as seed is actually a bony drupe, enclosed in a thick felty covering, which contains 1-3, occasionally four, true seeds. The most frequent number of seeds per drupe is one only, and completely empty drupes are common, 20-50 per cent of the total. There are between 1200 and 3100 drupes kg-1, the number varying according to the provenance. They are nearly always sown intact, and no attempt is made to extract the seed. Indeed extracted seeds give much lower germination percentages than whole drupes (Suangtho, 1980). The drupes retain their viability for a long time, and may lie dormant on the forest floor for many years. They can be stored quite easily in well-aerated sacks at room temperature, but must be kept quite dry. One-year old drupes give better germination than fresh ones.
If untreated the drupes germinate slowly and irregularly often over a period of a year or more. Thus many methods have been recommended to accelerate and improve germination. Some of these are listed by Lamichhaney (1982), and his list is far from exhaustive. There is some evidence that drupes of different provenances differ in their response to differing treatments. Actually in many countries where T. grandis is raised on a large scale, and abundant supplies of seed are available, the technique in practice is to sow very large quantities of seed and accept low germination percentages.
Suangtho (1980) did a number of experiments on T. grandis seed germination at the Australian National University at Canberra. His conclusions were that good germination can be obtained by heat treatment of the seed before it is sown, either for 1-2 weeks at 50°C, or for a few hours up to 48 hours at 80°C. Soaking the seed in water during the treatment gave no advantage and was frequently harmful. Sowing in sand with a moisture content of about 11 per cent gave the best results.
Under field conditions exposure of the seed to controlled high temperatures will rarely be practicable, unless drying ovens are available. A suggested method is as follows: spread out the seed (preferably one year old) in a thin layer on hard ground or concrete in the sun, with plastic sheeting over it to increase the temperature, but keeping it dry, continuing this treatment for 4-5 weeks. Then sow the seed in sand, without shade, with the point of attachment of the fruit stalk downwards, by pushing the seed into the sand until the base is just covered. Water twice daily, giving a thorough soaking. As individual seeds germinate, prick them out into beds or plastic pots.
The commonest and most satisfactory method is to raise T. grandis as stumps. Seedlings are sometimes raised in polythene bags to supplement stumps as they can be raised in 3-4 months in the nursery, whereas stumps need a year.
For raising as stumps, pre-treated seeds may be sown in beds early in the rams 10 drills 5-8 cm apart, with the seeds touching each other in the drills. However a better method is to use pre-germinated seed and prick them out at a spacing of 15 cm x 30 cm in the beds. This gives ample room for the seedlings to develop; if the seed is sown in beds without being pre-germinated. It often produces a very congested stand of weak seedlings: There should never be any shade, and watering is unnecessary except immediately after sowing, if there should be a dry spell, but the beds should be kept free of weeds by hoeing between the seedlings. This should produce plantable stumps 1-2 cm. 10 diameter at the collar by the first pre-monsoon rains. Beds used for raising stumps will need either to be given artificial fertilizers, or to be rotated with a leguminous crop to maintain soil fertility.
In Thailand it is the practice to lift the plants about February, and make them into stumps with 2 cm of stem and 13 cm of root. All secondary roots are scraped off the taproot. The stumps are then tied into bundles and stored between layers of very fine dry sand in pits 1.5 m deep. A thatched shed is built over each pit, to keep it dry, and also to keep it as dark as possible. The stumps thus prepared are planted in the first rains in April. It is claimed that such stored stumps give better results than stumps lifted directly from the nursery, as when they are planted they are still dormant, whereas plants from nursery beds will already have begun to put out new leaves and are more likely to suffer damage if, for example, the rain after they have been planted is less than normal.
Seedlings may be raised in polythene pots by sowing the seed in February or March. Because of the very erratic germination of T. grandis seed, It is essential that pre-germinated seeds should be used, sown at one seed per pot. Such seedlings win of course need to be watered, but no shade is needed. Seedlings raised in pots are useful when, for instance, by some mischance insufficient stumps have been raised, or if there is only a short time before the planting season in which to raise nursery stock. Otherwise stumps are preferable.
The best time for planting stumps is during the pre-monsoon rains, as soon as the soil is wet to a depth of about 20 cm. If stored dormant stumps are used they can be planted at the time the pre-monsoon rains are expected. If no rain falls they will remain dormant and alive for at least 2-3 months. It is very important to plant the stumps as early in the rains as possible; delaying planting until July will mean the loss of most of the first season's growth. Container-raised seedlings should be planted with the first monsoon rains. It is not necessary for make pits before planting: a hole just large enough to take the stump is sufficient, but the soil must be well firmed round the stump. Spacing should preferably be 2 m x 2 m or 2.5 m x 2.5 m; if growth is satisfactory this will enable a first thinning to be made when the trees are aged 5-7 years. For planting under taungya a wider spacing, say 4 m x 2 m, may be necessary to allow cultivation between the trees.
Tectona grandis will withstand a certain amount of grass and weed competition in that the plants will remain alive and gradually struggle up through them, but for a satisfactory plantation thorough weeding is necessary. If taungya cultivation is possible, this will give the best results. If teak has been planted at 2 m x 2 m or 2.5 m x 2.5 m it can be given a first thinning when the trees are 7-10 m tall. This can be a systematic one, removing every alternate tree. In a good plantation this height should be attained by the age of about five years. Subsequent thinnings should be made at about five-year intervals during the early life of the plantation, extended to ten years as the trees grow older. Timely and regular thinning is necessary; if thinnings are delayed the trees take a long time to respond once they are thinned.
Apart from very young plantations, in Nepal measurements are available from only one older plantation, at Sagarnath (M.R. Joshi, 1982). This was planted in 1971, using seed from Gorakhpur in India, on an alluvial site with a permanent water table 7m below the surface. The original spacing was 8 ft x 8 ft (2.4 m x 2.4 m) equivalent to 1680 stems ha-1. The plantation was thinned lightly when seven years old, but the volume removed was unrecorded. At 10.5 years old there were 1330 stems ha-1, with a mean dbh of 14 cm, a top height (100 largest trees per hectare) of 19.3 m, a basal area of 22.1 m2 ha-1, and a volume over bark (to 5 cm top) of 152.5 m3 ha-1. This is equivalent to a mean annual increment of 14.5 m3 ha-1, excluding the thinning at seven years old.
These growth rates are equivalent to Quality II in Laurie and Ram's yield tables (1940) but the highest quality in these tables is mostly from Burma. They fall within Quality I of the tables for Nilambur teak in Kerala, India, (Troup, 1921). Hence the growth rates in this plantation are very satisfactory, though admittedly it is on an unusually good site. It demonstrates that high quality T. grandis plantations can be grown in Nepal on certain sites. A little information is available from younger trials. In another plot at Sagarnath trees five years old had a mean height of 7.6 m and a mean dbh of 4.7 cm (KJ. White, 1988). This is about equivalent to Quality III of Nilambur teak, with, as far as can be estimated from this very early growth, an eventual mean annual increment of between 4 and 5 m3 ha-1.
The mean annual increment of T. grandis in India is mostly between 4 and 8 m3 ha-1. For timber production the rotation on good sites is likely to be between 60 and 80 years, but on poorer sites it may be much longer. For more details on growth in India see Laurie and Ram's (1940) yield tables.
Tectona grandis timber is world famous and is in high demand on world markets being ornamental, durable, and relatively easy to work. Previously in places where T. grandis was abundant it was very widely used for all types of house-building, ships and boats, furniture and even railway slippers, but nowadays, as T. grandis is becoming increasingly scarce and high in price, there is a tendency to use it for higher value products such as veneers, rather than for general construction work. It weighs about 720 kg m-3.
It is an excellent fuel, and in the 1920s and 1930s teak plantations in parts of Africa were managed on a coppice rotation for fuelwood production. However in view of the high value of its timber this practice has now been largely abandoned. Although the heartwood is extremely durable, the sapwood is not, and in some places is very susceptible to attack by powder post beetles. This limits the use of small poles for some purposes.
Some plantations have been established in the Bhabar Terai and Terai zones; at least one is of excellent quality, but others are rather disappointing. This may be due to due to unsuitable sites, to poor tending, or a combination of both. It does appear, however, that good T. grandis sites are not very common. The main need in the Terai is for fuelwood and for this purpose there are certainly species which will produce a higher yield than T grandis. However, there is also a national demand for high quality timber, met at the moment largely by Shorea robusta, but supplies of this are dwindling. In areas where suitable sites can be found and since good T. grandis soils are often good agricultural soils, there may be difficulties there would seem to be a case for at least a small scale programme of T. grandis plantations. It should also be borne in mind that a third grade T. grandis plantation may be more profitable than a first grade plantaion of less valuable species. However there does seem to be a need for more discrimination in deciding on which sites T. grandis should be planted.