INTRODUCTION
Teak (Tectona grandis Linn.f.), an important timber species of worldwide reputation (Banik, 1993) has indigenous distribution in Peninsular India, Myanmar, Thailand and Laos. It is believed to be an early introduction in Java (White, 1991). Outside its natural habitat, it is cultivated in South and South-East Asia, the Pacific, Africa, the Caribbean Islands, South America and Central America (Tewari, 1992), accounting for 14% of tropical forestry plantations (Evans, 1982).
Although systematic planting and management of teak dates back to the 1840s, a number of problems have been identified in maintenance and improvement of productivity in plantations. The commercial interest in shortening rotation may complicate management practices for want of enough growth data under high fertilizer and irrigation inputs. Apart from this, the impact of intensive high input forestry on sustainable production is also not clear.
This paper reviews the traditional plantation techniques and highlights various issues associated with management and productivity of teak in plantations.
TRADITIONAL PLANTATION TECHNIQUE
Teak forests are regenerated artificially, except in the dry teak forests, which are worked under a coppice system, or for the moister forests where the advance growth is cut back to form the new crop. The common practice is to raise new crops using root-shoot cuttings (stumps). This procedure has been going on for over a century in India. Various techniques of artificial regeneration have been more or less standardised, although there is scope for further improvement. More than knowledge about correct technique, a correct programme of work and its execution according to schedule is critical (Tewari, 1992).
Seed collection and nursery
Seed collection, storage and pre-sowing treatment
'Seeds' (technically fruits) are collected from the ground as and when they fall during January and February. The bladder-like calyx is removed by vigorously rubbing it inside a gunny bag. The seeds are then cleaned by winnowing. Seeds store well in gunny bags or sealed tins for 2-3 years.
The stony hard pericarp poses a problem for quick and uniform germination. In order to hasten germination, various pre-sowing treatments have been developed.
Some of the beneficial treatments include: 1) alternate soaking in water and drying for 24 hours each for two weeks; 2) immersing the seed in water for a number of days; 3) soaking the seed in a mixture of cowdung for a period up to one week; 4) putting the seeds in alternate layers of seed and sand in a pit with daily watering for 7 days, and then drying and storing till time of sowing; and 5) spreading the seed in a 10 cm layer in the sun on a mat or cement platform and watering constantly until commencement of germination.
Nursery site, preparation of beds, and seed rate
Well-drained sandy loam with gently sloping terrain is recommended for preparing nurseries.
Each bed is of 1.2 m (12 m size, spaced at 0.3 m to 0.6 m between beds and 0.6 m to 1.6 m between rows of beds. Each bed produces about 400-800 plantable stumps. The ground is ploughed and the area of the bed is dug out to a depth of 0.3 m. Roots, stumps and stones are removed. The clods of earth are broken fine. The soil is allowed to weather for about a month and then filled into the nursery bed with sand and organic matter. However, when temporary nurseries are established in forest areas rich in nutrients, no additional manurial inputs are necessary.
In moist localities the beds are raised to a height of 30 cm from ground level to prevent water logging. In dry zones, beds are made flush with the ground level. In very dry localities, with a mean annual rainfall of 750 mm or less, slightly sunken beds give better results.
The seed rate per standard bed of 12 m (1.2 m varies from 3 kg to 12 kg. At Nilambur in Kerala, about 5kg of seeds are commonly used.
Method of sowing of seed in seed bed and maintenance
Both broadcast sowing and line sowing or dibbling 5-10 cm apart are practiced. Line sowing or dibblings have greater seed economy and better survival and growth. Beds normally do not need any overhead shade. Irrigation is not provided except in very dry areas. Beds are maintained free of weeds.
Plantation establishment
Selection of site
The site for planting may be either plain or gently sloping with excellent drainage. Soils derived from gneisses, schists and trap are good for teak. Alluvial sites are superior for teak growth while laterite or lateritic gravel as well as clays, black cotton, sandy and gravely soils derived from sandstone are not good for teak plantations.
Preparation of planting site
After removal of saleable material, the site is given a burn to dispose of the slash and improve access and fertility. A study conducted by the Kerala Forest Research Institute (KFRI) indicates that slash-burning does not help to improve the growth of teak beyond the first year (Chacko et al., 1991).
Method of raising plantations
Stump (a root-shoot cutting) planting is the popular method of raising plantations. Stumps with a 1-2 cm diameter (at the thickest part, referred to as 'stump thickness') prepared out of one-year-old seedlings are planted in holes made with a crowbar. In dry localities, where rainfall is less than 900 mm, pre-sprouted stumps raised in polythene containers a few months in advance give satisfactory results. Direct sowing and transplanting of bare-root seedlings, though practiced in some areas, do not give satisfactory results.
Method of planting and spacing
Stumps are planted in crowbar holes and generally buried up to the collar. In drier localities stumps are planted flush to the ground. In hard soil, it is practiced to plant stumps in pits of 30 cm deep and 15 cm diameter.
Although spacings of 1.8 m (1.8 m to 3.6 m (3.6 m are practiced in different regions, 2 m (2 m is the most common.
Weeding
Weeds, especially grasses, retard teak growth and therefore are managed below the level of competition either by fork weeding, scrape weeding, uprooting or knife cutting at ground level. The number and intensity of weedings vary with the intensity of weed growth.
Intercropping
Intercropping in teak plantations (termed as 'taungya') during the initial two years of planting is a common practice where there is a demand for cultivatable land. Once the plantation area is leased out, the cleaning of the site, burning, staking and planting are done by the lease holders. The common intercrops are paddy, chillies, maize, wheat, sesame and various vegetables. Crops such as sugarcane, wet rice, plantain, jute, cotton, or creeping vegetables such as pumpkin and cucumber are not allowed. During the growth of the field crop, the weeding and tending of teak are done by the lease-holding farmers. However, in certain regions the practice of 'taungya' has been discontinued for reasons of soil degradation and suppression of teak (Alexander et al., 1980).
Plantation maintenance
Weeding and cleaning
Generally two to four weedings a year are required in plantations during the first three years. Scrape weedings can effectively control weeds. Cleaning is done in areas where bamboo forms the main understorey.
Thinning
Thinning prescriptions vary from one locality to another. Unfortunately, it is often governed by revenue rather than silvicultural considerations. In a good quality plantation, managed on a 50 year rotation, the thinnings are carried out at the fourth, eighth, 12th, 18th, 26th and 35th years. Thinning schedule varies with site quality. In better plantations the thinnings are done early as compared to poor plantations. The first two thinnings in plantations with an initial spacing of 1.8 m (1.8 m or 2 m (2 m are mechanical wherein 50 % of stock is removed in each thinning. Alternate diagonals in the first thinning, and alternate rows in the next are thinned. Climber cutting and cutting back of overtopping bamboos and other species are done during the early thinnings.
Reference: Management of Teak Plantations, Overview of problems in teak plantation establishment - Dr. Apichart Kaosa-ard (accessed online at
Management of Teak Plantations)