3 Physiological and technical issues

3.1 Bio-ecological requirements and growth

Most of the data of the bio-ecological requirements of teak in Central America comes from the experience of, and the studies done, in Costa Rica, and a little from Panama and El Salvador. Vásquez and Ugalde (1995) identified the following aspects in 14 sites located of the Guanacaste province, in the North Pacific region of Costa Rica,

• Best sites for teak are located in areas with medium to flat slopes, at the base of a mountain or in valleys and, in areas where the soil's depth is 90 cm or more. These sites allow more space for root growth, and have more water and nutrients available, with a calcium content higher than 10 meq/100 ml of soil in the first stratum.
• Sites classified as highly productive have rainfalls higher than 2000 mm/year. It is important to mention that the evaluated zone is the Dry Pacific of Costa Rica, with a 3 - 5 dry month period.
• Worst sites for teak are those affected by strong winds, soils area shallower than 80 cm, with high iron and low calcium contents. These areas are generally located in summits, in over-pastured soils, with rainfalls lower than 1800 mm/year.
• Plantations with a dominant height of 21.7 meters or more, at 10 years of age (base age), are classified as highly productive. Plantations with a dominant height lower than 18.1 m, at the same age, are classified as low productive.

Table 3 shows the increments in diameter, height, basal area and volume for high, middle and low productivity sites.

Table 3. Yields for Tectona grandis in Guanacaste, Costa Rica

Source: Vásquez and Ugalde (1995)

Vallejos (1996), in the same zone that Vásquez and Ugalde (1995) studied, determined that calcium content (0 - 20 cm of depth) influences significantly the yield of teak. He found that 18 cmol/l and more are adequate for good teak development. When soil present lower quantities, it is recommended to correct it with lime applications. He also determined that water deficit influences negatively the development of teak.

In this study, a Site Index prediction model was developed:

Ln (SI) = Ln (Hdom) + 1.8253 * ((1/Age^^0.5162) - (1/Base Age^^0.5162))

Where:

Ln = the natural logarithm
SI = site index
Hdom = dominant height (meters)
Base age = 10 years

Furthermore, a model relates the SI to the soil calcium content (Ca) and water balance (DEFHID):

SI = (25.432112 - 2.695521 * DEFHID + 0.268667 * Ca)/0.794

Where:

DEFHID = the number of months with less of 100 mm of rainfall.
Ca = the content of calcium (cmol/liter)

Vallejos (1996) developed a five class production/yield index for that area. Table 4 displays the information. Table 5 summarizes the conditions for good teak growth in Costa Rica.

Table 4. Yield and production classes for Tectona grandis in Guanacaste, Costa Rica

Source: Vallejos (1996)
Vol = total volume with bark in m³

In Central America, teak has been planted in the dry forest zone as well as in the humid forest. Given the wide range of climatic, edaphic and topographic conditions in which it has been planted, there is enough experience to indicate the conditions under which it is more likely to obtain better growth and yields.

Ugalde (1997) indicates that, with the experience in Central America, the following aspects have to be considered:

• Temperature: The limits are an average of 25 and 28 degree Celsius, classified as good. Outside of those temperatures, the species does not grow well.
• Rainfall: Teak grows well between 1 250 and 2 500 mm/year. The species requires a 3 to 5 months dry period per year.
• Elevation: In Central America, the best yields have been obtained under 600 meters above sea level.
• Soils: Teak does well in sandy and slightly clay, fertile, deep, well drained soils, with a neutral or slightly acid pH.
• Limiting factors: It is not recommended to plant teak in steep slopes; compacted or shallow soils and; heavy textures.

Table 5. Bio-climatic considerations for planting teak in Costa Rica

Source: Picado (1997)

*Limiting condition or variable. **Detailed values or specifications.

The MADELEÑA Project established sample plots in all countries. The results are summarized below (Ugalde 1997):

• Honduras: There are reports of a breast height diameter MAI of 2.29 cm/year in the Atlantic Coast and 1.05 cm/year in the north zone, coupled with height MAI’s of 1.75 m and 1.0 m, respectively.

• El Salvador: Some studies indicate an MAI in breast height diameter between 1.6 and 2.5 cm/year and a MAI in height between 0.8 to 2.9 m/year.

na = not available

• Nicaragua: The studies reported a maximum MAI in height of 1.9 m/year and a maximum MAI in diameter of 2.2 cm/year.

na = not available

• Panama: diameter increments of 1.2 and 3.2 cm/year and in height between 0.18 and 3.4 m/year have been reported.

Flora y Fauna S.A. reported volume MAI increments between 9.3 and 22.9 m³/ha/year in plantations located in the North Zone of Costa Rica (Table 6). The Flora y Fauna Company has a set of production tables for the different sites of their plantations.

Table 6. Summary of four production scenarios (total and commercial volume) established for Flor y Fauna S. A. (plantation for a 20-year rotation). San Carlos, Costa Rica

Source: Camacho (1998)

Annual increments in diameter, height and volume in Bosques de Puerto Carrillo were obtained from permanent sample plots. The project information is presented in Appendix 5. Some average parameters obtained from the permanent sample plots are summarized in Table 7.

Table 7. Technical information from Permanent Sample Plots (PSP) of Bosques de Puerto Carrillo’s teak plantations. July, 1998

Source: Quirós (1998).

n.s. = non-significant

V_tot = Standing volume according to Keogh's formula (1980), V_tot = 0.0359 + 0.000022 D_g² * H_med * N;

V ₁₀ = Useful volume up to a minimum diameter of 10 cm without bark.

Table 8. Expected teak growth and yield per hectare in a high quality site with minimal management in Costa Rica

Source: Picado (1997)

^a: Commercial height up to a diameter of 10 cm with bark;

^b: Gross commercial volume = (dbh/100)² * 0.7854 * Commercial Height *ff; where: ff = estimated form factor of 0.65.

Picado (1997) proposed a plantation management structure and possible yields to be obtained in Costa Rica. According to his projections, after 20 years, the MAI commercial volume will be 19.4 m³/ha/year (Table 8). Therefore, the structure can be considered representative of the average teak production conditions in the country.

Zambrana (1998) reported preliminary data for young plantations from El Salvador, 214 m³/ha of commercial log volume (8 cm top diameter) for 25 rotation age. Table 9 shows the proposed thinning plan and commercial volume yields.

Table 9. Preliminary yields estimates for teak in El Salvador

Source: Zambrana (1998)

3.2 Plantation management system

To produce timber for sawmills, Picado (1997) recommends planting 1,000 - 1,600 trees/ha. In Costa Rica, in a high quality site, the first thinning must be performed between the third and fourth year. About 40 -50% of the total tree number has to be removed. Generally, this thinning does not yield any commercial timber, but it is necessary to eliminate competing, malformed, sick or damaged trees.

Until now, Costa Rica’s teak plantations management has been "poor and inadequate". Poor because the owners do not wish "to lose" 400 to 500 trees, that represented an investment during first three to four years, and inadequate because they don’t have enough technical knowledge. The result damages the plantation productive potential, reduces the size of the logs and limits the timber supply of better quality logs in the short term.

Martínez et al (1994) indicate that 62 % of the forest plantations of small and medium size farmers, with economic support from the State and technical direction from organizations of forest producers, showed management problems (lack of pruning and thinning).

Table 10 presents examples of estimated teak rotation, based on diameter increments values of 1.5 and 2 cm/year. For a 20 years rotation, average diameter at the final cut will be 30 - 40 cm. For a 25 years rotation, average diameter will vary between 37.5 and 50.0 cm. However, it is important to clarify that it is tantamount a good site selection and timely management to reach the maximum productive potential of the site.

When the diameter increment is equal or bigger than 2 cm/year, the convenient rotation is 20 years, with trees of an average of 40 cm (dbh). Financial analysis shows that rotations of more than 25 years presented IRRs lower than 12%.

Table 10. Estimated rotation age for teak plantations in Central America

Source: ¹ Quirós (1998), ² Víquez (1998), ³ Camacho (1998), ⁴ Becker (1998), ⁵ Morán (1998) and ⁶ Zambrana (1998), June, 1998.

The University of Wageningen is developing yield tables for three productivity index in the Dry Pacific and Atlantic Zone of Costa Rica (de Vriend 1998, unpublished thesis).