Management of Natural Teak Forests

Management status of natural teak forests - U Ko Ko Gyi and Dr. Kyaw Tint

Ko Ko Gyi and Kyaw Tint

Forest Department, Ministry of Forestry, Yangon, Myanmar

Natural teak forest management practiced under the Myanmar Selection System

ABSTRACT

Teak is an all around premier species of many favourable properties and will remain as one of the most admired and precious trees. It is indigenous to only four countries, India, Myanmar, Thailand and Lao PDR, and its forest associations and classifications are described. Natural forest management in these countries is discussed. The history of the Myanmar Selection System and the operational features of the selection felling effect on growing stock, species composition and stand structure are noted. Growth of stands and individual trees and growth simulation studies are described and country production and exports are discussed together with such practices as the girdling of teak and logging systems. Continuous monitoring has been established (Myanmar) for planning and noting data changes in the resource, yield calculation and simulation models. Future yields are estimated but with only Myanmar showing sustainable potential for export. It is essential to apply a multi-disciplinary approach to ensure sustainable management of natural teak forest for present and future generations.

Key words: Tectona grandis, Myanmar, natural forest management, girdling, simulation model, yield.

INTRODUCTION

Teak (Tectona grandis) is an all around premier timber with many favourable properties and has been, and will continue to be, one of the most admired and precious timber tree species in the world. It is indigenous to only four countries, and dense natural forests with big and beautiful admiralty quality teak have degraded and shrunk so rapidly that at present they are confined only to Myanmar and to some extent to India. Natural teak has now almost become an endangered species.

Under these circumstances it is of vital importance to: conserve, improve and expand the remaining natural teak stands; restore teak forest ecology; promote sustainable utilization of this invaluable natural asset and employ management systems guided by the forestry principles adopted at the Earth Summit. In this context it is crucial for the teak experts, teak producers and teak consumers to meet, to overview the state of technology of natural teak forest management in the countries of origin, and to exchange ideas and contribute to the sustainable development of natural teak forests.

The paper presents the past and present status of management of natural teak forests in India, Myanmar, Thailand and Lao PDR where the species is endemic (with a focus on natural teak forest management in Myanmar. Information from countries other than Myanmar may be inadequately presented.

NATURAL DISTRIBUTION

Teak is indigenous to the South and Southeast Asian countries of India, Myanmar, Lao PDR, and Thailand. The species is also well established in Indonesia on the islands of Java and Muna, but it is not clear whether this occurrence is natural or results from an introduction by Hindus in the seventh century (Howard, 1948; Letourneux, 1957; and Van Alphen De Veer, 1957).

The area of the natural teak forests in India (Tewari, 1992), Laos (Anon., 1993), Myanmar (Pengduoang, 1991), and Thailand (Kaosa-ard, 1991) is shown below. The total amounts to 27.9 million ha.

India

Teak is mostly confined to the Peninsula region below 24°N latitude. This region is bounded in the north by the Western Arvallis of Rajasthan. The dividing line passes eastward through the districts of Jhansi and Baroda in Uttar Pradesh, finally curving southeast to the Mahanandi river through Madhya Pradesh and Orissa. From this northern limit, teak extends south-wards through the states of Madhya Pradesh, Maharashtra, Andhra Pradesh, Tamil Nadu, Karnataka and Kerala. The distribution of the species is discontinuous and non-teak areas of varying extent are frequent. The more important teak forests, however, occur in Hoshangabad Betul (Madhya Pradesh), Chanda and Melghat (Maharashtra) Wynaad (Kerala), Anamalai hills (Tamil Nadu) and North Kanara (Karnataka) (Wood, 1992). Natural teak forest in India covers about 8,900,000 ha (Tewari, 1992); based on rainfall, this forest is classified into five types as shown in Table 1 (Kumaravelu, 1991).

Table 1. Classification of teak forest based on rainfall

Laos (Lao People's Democratic Republic)

Teak occurs naturally in the northwest in the provinces of Xaignabouli (Sayaboury) and Bokeo. These are continuations of the natural teak forests of Myanmar and Thailand and cover about 16,000 ha (Pengduoang, 1991). Teak grows mixed with bamboo, Lagerstroemia, Hopea, Dipterocarpus and Shorea species.

Myanmar

Natural teak forest occurs within 25°30'N and 10°N latitude. On the east, teak occurs throughout the Shan State and extends beyond the frontier into Thailand and Laos. In the northwest it does not extend beyond the western watershed of the Ayeyarwady and Chindwin rivers; in the southwest it occurs on the west bank of the Ayeyarwady into the foothills of the Rhakhine Yomas in decreasing abundance to approximately 18°N latitude. It does not occur in the dry zone of central Myanmar, or in the tidal regions of the delta area, or in those areas of elevation exceeding 914 m. Teak forest in Myanmar covers approximately 16,517,700 ha (Anon., 1993).

MAP 1. Showing natural distribution of teak

MAP 2. Teak bearing forests of Myanmar

The forests in Myanmar are classified into six major forest types. Natural teak distribution occurs in the semi-evergreen forests, mixed deciduous forests and deciduous dipterocarp or Indaing forests. These forest types with their sub-divisions are given below.

Evergreen forests

• Tropical wet evergreen forests
• Tropical semi-evergreen forests

Mixed deciduous forests

• Moist upper mixed deciduous forests
• Dry upper mixed deciduous forests
• Lower mixed deciduous forests

Deciduous dipterocarp or Indaing forests

• Indaing forests
• Semi-indaing forests

Dry forests

• Than-Dahat forests
• Thorn forests
• Aukchinsa-Thinwin forests

Hill and temperate evergreen forests

• Sub-tropical wet hill forests
• Sub-tropical hill savannah forests
• Alpine forests

Tidal, beach and dune, and swamp forests

Teak in the semi-evergreen forest is usually found as scattered individuals or in small groups with little or no regeneration present (Kermode, 1964). Trees are generally large and may be associated with Michelia champaca, Tetrameles nudiflora, Dipterocarpus species, Eugenia species, Cedrela species, etc. Undergrowth may consist of bamboo such as Dendrocalamus hamiltonii and Cephalostachyum pergracile and of small evergreen trees or shrubs.

In the lower mixed deciduous (LMD) forest, teak may be found gregariously or in patches. The species attains a large girth and height and trees are greatly fluted in these forests. Teak is usually found in association with Anogeissus acuminata, Homalium tomentosum, Terminalia tomentosa, etc. Bamboo is almost absent in this forest type.

The moist upper mixed deciduous (MUMD) forest produces teak with cleaner and straighter boles (Kermode, 1964). Here it is associated with Xylia kerri, Pterocarpus macrocarpus, Gmelina arborea, Bombax insignis, etc. Bamboo species, such as Bambusa polymorhpa and Cephalostachyum pergracile, are found in this forest type. Dendrocalamus hamiltonii is also found in northern Myanmar.

The dry upper mixed deciduous (DUMD) forest produces teak of poorer quality than in the MUMD forests. Natural regeneration is frequent. In this forest type, teak is usually found associated with the same species as in MUMD forests with a few additional dry forest species, such as Shorea obtusa, Pentacme siamensis and Acacia catechu. Bamboos, as Thyrostachys oliveri in northern Myanmar and Dendrocalamus in the south, are also associated with teak in this forest type.

In Indaing (deciduous dipterocarp) forest, teak does not grow to a great size and is of poor quality. Regeneration is often abundant and the species is found in association with Dipterocarpus tuberculatus which may comprise as much as 80%, or more of the crop (Kermode, 1964). Semi-Indaing forests are usually found with an abundance of poor quality teak. Regeneration is also profuse; teak grows mixed with Pentacme siamensis and Shorea obtusa.

Thailand

Teak occurs within a latitudinal range of 16° to 20°N and a longitudinal range of 97° to 101°E. It is found in mixed deciduous forest throughout the northern part of the country and covers about 2,500,000 ha (Kaosa-ard, 1991). The associate species are Pterocarpus macrocarpus, Xylia kerii, Afzelia xylocarpa, Lagerstroemia calyculata and bamboo. The teak distribution pattern is discontinuous or patchy.

MANAGEMENT SYSTEMS

India

Natural regeneration is normally employed in the greater part of the teak growing areas apart from Kerala, Tamil Nadu and parts of Maharashtra where artificial regeneration is employed (Kumaravelu, 1991). The silvicultural systems practiced are: the coppice system, clear felling with conversion to uniform system and a selection system with improvement fellings.

In the very moist forests of semi-evergreen nature vegetation, a selection-cum-improvement felling system is applied. Planting is also carried out in suitable small areas. In the high teak forests of Madhya Pradesh, which are worked under conversion to uniform forests, a conversion period of 60-80 years applies.

Inferior or low quality forests are managed on a coppice system with rotations of 30-40 years. The system is applied only in portions of the coupe not prone to frost damage and containing adequate coppicable stock and advanced growth. This is not applied in forest patches containing well-stocked patches of teak poles, or with saplings or advanced growth of miscellaneous species up to a girth of 30cm, or containing 75 to 100 standards per hectare of more valuable species of 45 cm girth, as such patches are excluded from felling (Kumaravelu, 1991).

Lao PDR

Felling of teak is nowadays prohibited (Pengduoang, 1991). Natural teak forests used to be managed in a selection system. The Ministry of Agriculture and Forestry limits the felling of teak by quota and felling is controlled by the Department of Forestry. Harvesting consists mainly of the collection of old logs in the forest from past fellings and from shifting cultivation; an average annual yield of 500 m³ is realised. Cutting of teak, however, does not take place every year. In an attempt to ensure regeneration, teak seeds are dibbled in the gaps where trees are removed. The forest floor is then burnt after leaf fall has covered the site.

Thailand

The management of teak forests under the Brandis Selection System started in 1896; a felling cycle of 30 years with a prescribed girth limit (gbh) of 213 cm was adopted in 1939. In this system, teak forest was broadly divided into two blocks (i.e., logging or opened, and non-logging or closed blocks). The logging block was subdivided into 5 (3 (i.e., 5 compartments and 3 felling series plots) for 15 years logging operations and concession. In 1953, the concession was revised and the overall teak forest was divided into 40 working plan units. Each unit was then subdivided into 30 felling series for a 30 year logging operation and concession. However, all teak logging operations and concessions were terminated in 1983. Only improvement fellings are permitted in the natural teak forests (Kaosa-ard, 1991).

Myanmar

Forest policy and forest law

Forest management in Myanmar developed over centuries. Myanmar kings formulated a complex system designed to maximize revenue and control. The teak trade was controlled by regulating extraction from the forest under a system of girdling, and Myanmar's involvement in the teak trade predated that of the Europeans. From at least the 17^th century, southern Myanmar exported locally built teak ships (Bryant, 1993). Systematic forest management was initiated in 1856. Until recently, the guiding principles had been derived from a policy document prepared in 1894. Now, they are enshrined in the Myanmar Forest Policy 1995.

The current policy recognizes the following six imperatives:

1. Protection of soil, water, wildlife, biodiversity and environment;

2. Sustainability of forest resources to ensure perpetual supply of both tangible and intangible benefits accrued from the forests for the present and future generations;

3. Basic needs of the people for fuel, shelter, food and recreation;

4. Efficiency to harness, in a socio-environmentally friendly manner, the full economic potential of forest resources;

5. Participation of the people in the conservation and utilization of the forests; and

6.

The policy prescribes inter alia: 1) to gazette 30% of the total land area of the country as reserve forest and 5% under a protected area system; 2) to introduce a system of environment pricing based on the "polluter pays" principle to compensate for environmental and ecological degradation; 3) to pursue a sound programme of forest development through regeneration and rehabilitation operations to optimize productivity from natural forest; 4) to recognize that plantation forestry is not a substitute for natural forest management; 5) to promote efficient harvesting and sustainable utilization of all forms of forest produce; and 6) to enlist people's participation in forestry sector development activities in order to provide "people-based development" and also create public awareness and mass motivation for the protection and conservation of forests.

The new Forest Law, in line with the Myanmar Forest Policy, focuses on a balanced approach towards conservation and development issues implicit in the concept of sustainable forestry. It decentralizes management and opens up opportunities for increased private sector involvement in the timber trade. Highlighting environmental and biodiversity conservation, the Law encourages community forestry and people's participation in forest management, but prescribes more severe punishments for forest offenses.

For management purposes the forests of Myanmar are organized in the following "working circles": 1) teak selection working circle (TSWC, 16.5 million ha); 2) non-teak hardwoods working circle (HSWC, 17.9 million ha); and 3) local supply working circle (LSWC, 0.5 million ha). The working circles are formed on the basis of accessibility and also on the nature and form of forest produce available. Occasionally, TSWC and HSWC overlap when non-teak hardwoods are also extracted in TSWC. Both working circles are worked under the Myanmar Selection System (MSS). In LSWC either coppice or coppice with standards systems are practiced.

The working circles consist of a group of reserves, which are further divided into felling series for the convenience of working according to the drainage and the geographical situation. Again, they are sub-divided into compartments on maps as well as on the ground; these are the basic management units. As for local supply reserves, annual coupes are the basic management units. They are similar to compartments, except that they are marked only on maps and are not permanently demarcated on the ground. Teak extraction is organised under the TSWC which includes all teak bearing forests.

Development of the Myanmar Selection System (MSS)

Dr. Dietrich Brandis arrived in Myanmar in 1856 to take charge of the Bago forests. He drew up the first Working Plan for Bago, based on ring counting and observation of trees of known age. He calculated that it took 24 years for teak trees between 4'6" gbh (44 cm dbh) to 6'0" gbh (58 cm dbh) to become yield trees of 6'0" gbh (58 cm dbh) and over. Accordingly he prescribed that 1/24th of the number of yield trees should be cut annually. The number of yield trees were estimated by Brandis from linear valuation surveys. This silvicultural system forms the basis for the management method known as the Brandis Selection System, which was modified into the Burma Selection System or Myanmar Selection System in 1920. As teak was the only commercial species at that time, management was designed to favour only teak. In later years, management of other commercially important species was also considered.

By 1920, the approved working plans covered 11,183 sq. miles (28,964 sq. km) with almost all the plans prescribing MSS with Improvement Felling (IF). The IF then was classified as O (old) and Y (young) felling according to the size of the crop to be assisted. Recording of teak trees 4'0" gbh (39 cm dbh) left standing at the time of girdling in each compartment was initiated in 1922. This provided a reliable basis for calculating the future yield and it was decided that future working plans would be based on these records.

Selection of teak trees for exploitation under MSS

Under the Myanmar Selection System, a Felling Series is divided into 30 blocks of approximately equal yield capacity. Each year, selection fellings are carried out in one of these blocks and the whole forest is therefore worked over in the felling cycle of 30 years. Under this system when felling becomes due, all marketable trees which have attained a fixed exploitable girth are selected for cutting. The fixed exploitable girth varies with the type of forests. In good (moist) teak forest, the girth limit at breast height (4'6" or 1.3 m above the ground) is 7'6" (73 cm dbh); and in poor (dry) forest 6'6" (63 cm dbh).

Unhealthy trees that have not attained these sizes but are marketable, are also selected for cutting if they are unlikely to survive through the subsequent felling cycle. If seed bearers are scarce, some high quality stems are retained as seed trees. Mature teak trees selected for exploitation are normally girdled and left standing for 3 years before being felled and extracted. This is to season the timber and make it floatable, as the logs are normally transported by floating them down the streams and rivers. However, in accessible areas mature teak trees are sometimes felled and extracted green. With regard to girdling teak, Brandis (1896) stated that: "this excellent practice, as a matter of course, I maintained, but one of the many battles I had to fight during my Indian career was against those who condemned this practice as useless, as barbarous, as injurious to the timber, and likely to damage the reputation of Burma teak, while others described girdling as the outcome of German theories. In reality it was an old Burmese practice, to which the good reputation of Burma teak was mainly due."

In the selection of natural teak trees for girdling or green felling, the compartments selected are first checked and the boundaries repaired. Each compartment is then combed along the contour and all teak trees 4'0" gbh (39 cm dbh) and over are measured and recorded while trees attaining the prescribed girth limits and over are selected and scrutinized as to whether they will yield marketable logs or not. If they can yield marketable logs they are girdled for exploitation. Some undersized defective trees, which will not last for another 30 years, but which will yield marketable logs, may also be selected for girdling. In areas where the stocking of teak is poor, a few mature teak trees may be left as seed mother trees.

Improvement fellings are carried out concurrently with girdling. In this operation, inferior tree species that are competing or suppressing teak trees are felled in favour of teak. Thinnings are carried out in crowded young teak stands.

Annual yield is estimated as

where ARR = annual rate of recruitment of Class II trees to Class I; CI = original no. of trees in Class I; FC = felling cycle (i.e. 30 years); and LP = decided period to liquidate original CI trees (usually 60 years).

Plantations play a minor role in Myanmar forestry. They are resorted to only for the restoration of the denuded areas. Myanmar sacrifices economic gains from plantation forestry to uphold its forest management which focuses on the sustainable development of natural forests in the interest of biodiversity conservation and environmental stability.

Effect of MSS on the condition of the forest

A. On the ground stock and species composition

To study the change of the growing stock of teak and its percentage composition, the inventory data collected during 1963-67 (=1965 data) are compared with those provided by 1981-83 inventory (=1982 data) in Table 2 to study the effect of MSS on the growing stock of teak and its percentage composition.

Table 2. Growing stock of the forests in Bago Yoma

Area = 519,000 acres or 207,600 ha

Unit: 1,000 trees

Source: Management of teak and hardwood stands for sustainable production (Ba Thwin & Saw Han, 1991).

Pyinkado = Xylia dolarbriformis.

As seen in Table 2, teak growing stock from 1965 to 1982 declined by 49,000 trees, i.e. approximately 1 tree per 11 acres. However, the quality of the forest had improved with increased teak composition of 16.2%. The composition of less valuable species decreased from 71.2% to 68.5% while the total growing stock decreased by about 19%.

B. On Stand Structures

The forests of Myanmar are rich and diverse in flora and fauna and are ecologically complex. These complex ecological factors trigger both seed production and germination in the natural state. Some species may be fire hardy, some fire tender; some may be light demanders and others shade bearers.

Teak, for example, is relatively fire hardy, light demanding and fast growing. In the early seedling stage, surface fire may destroy above ground shoots, but the root portion will send up a new shoot again in the early rains. This process goes on for a number of years until conditions are favourable and the root is developed enough to send up vigorous shoots that can escape from ground fire damage. On the other hand, pyinkado (Xylia dolarbriformis), the second most important species, is not so fire resistant and unlike teak, it is a shade bearer.

Another factor that influences natural regeneration in the forests of Myanmar is the time when bamboo flowers gregariously. This occurs in a cycle of 30-60 years, after which they die. The death of the bamboo creates large openings, allowing more light and space to the existing advance growth and consequently natural regeneration is greatly promoted in such areas.

All these seedlings, regenerated in different ways, contribute to the stand structure of the forests which includes large, medium and small size trees. In sustained yield forest management, tree populations are maintained in a "normal" or "balanced" or "desirable" stand structure with higher number of small trees and sloping down as the size increases.

Stand structures of teak in the natural teak bearing forests are presented in Diagram 1 according to the inventory data of 1982 to 1986. The inventory covered a total area of about 21.8 million acres (8.72 million ha).

Diagram 1. Stand structure of teak - teak inventory data line graph

Although not normal, stand curves above 4' girth (39 cm dbh) are satisfactory in the majority of the Forest Divisions. Obviously in some, the population of smaller trees is inadequate indicating the need for intensive improvement fellings and other tending operations, better still if assisted by enrichment plantings.

GROWTH AND YIELD

India

In India stem analysis has been done extensively to study individual tree growth. Stem and stump analysis conducted for an average quality in Chittiyal Block in Warangal State and Hoshangabad Division provided the following information (Tables 3 and 4) on the growth of individual teak trees. A stem analysis for good quality teak (i.e., MP quality II-III) in Hoshangabad Division (Kuljarni, 1946) indicated the growth of teak trees as shown in Table 4 and from a stem analysis of this Table data the following observations were made:

• In 80 years teak attains a girth at breast height of about 1.31 metres.
• The MAI of standard stem timber volume under bark culminates slightly after the age of 80 years.
• 80 years is roughly the age at which the teak trees start degrading. The superior quality trees, however, remain sound even for a longer period while the poor quality ones degrade earlier.

The MAI and CAI have been recalculated by the author (Table 4), as the original calculations are not correct. But some observations are not precise and data is doubtful. For example, MAI was still increasing up to the age of 90 years but the observations say it culminates slightly after 80 years; the teak trees in Table 3 with 16.7 m in height and 30 cm in diameter had a volume of only 0.20 m³, while a much smaller tree in Table 4 with 12.5 m in height and 27.4 cm in diameter had a standard timber volume of 0.52 m³, more than two and a half times. So, the volume estimates need improvement. Considering height and diameter growth, only the trees in the Warangal Division grow much faster than those in the Hoshangabad Division.

Table 3. Stem and Stump analysis data in Warangal State

* Under bark

Table 4. Stem analysis data in Hoshangabad Division

Thailand

Teak in rich, deep soil with adequate moisture may attain more than 213 cm in girth, which is the girth limit for cutting in 60 years. But under unfavourable conditions it may take 250 to 300 years to reach the same size; the average is about 150 years. A study in northern Thailand showed that teak took 85 years to reach 213 cm in girth on alluvial soil, 113 years on soil derived from limestone, 160 years on soil derived from shale and sandstone and 170 years on soil derived from metamorphic rocks. A stump analysis of 400 teak trees occurring in different parts of the north indicated girth and height growth of individual trees as shown in Table 5. Height and diameter values are derived from a hand drawn curve (Tewari, 1992).

Table 5. Stump analysis data in northern Thailand

Myanmar

Growth of individual trees

Systematic studies on the structure, growth and yield of natural teak forests of Myanmar may be said to start with the commencement of the working plan operations in December, 1883. The first working plan prepared by J.W. Oliver was completed in June 1884 and by the end of June 1910, forty-four working plans for forests containing teak had been sanctioned. Using these working plan figures, Troup (1911) analysed the growth and yield of teak forests and published the results of his analysis in 1911. This growth rate of teak trees was estimated by counting stump annual rings and averaged by individual reserves or group of reserves to get the rotation age. Mean annual girth increment was computed by dividing the girth at breast height by the corresponding stump age.

The fastest, the slowest and the average for the whole of Myanmar mean annual girth increments were presented by sizes of 3', 4'6", 6' and 7' girth (approximately 29, 44, 58 and 68 cm in diameter respectively). The mean annual girth increment (averaged for the whole of Myanmar) of a yield tree of 7' girth (68 cm dbh.) was found to be 0.542 inches (0.438 cm dia. growth) with stump age of 155 years. The highest girth growth rate of 0.764 inches (0.618 cm dia. growth, stump age = 110 years) was observed in the Kangyi, Satpok, Sitkwin and Thindawyo Reserves. The slowest girth growth rate of 0.442 inches (0.357 cm dia. growth, stump age = 190 years) was noted in the Ziyaing and Mehaw reserves. As far as individual trees go, the maximum girth growth rate of 2 inches (1.617 cm dia.) was reported in the Ngalaik Reserve and the minimum of 0.24 inches (0.194 cm dia.) in the Sinthe Reserve. Troup also deduced from stump analysis data the ages corresponding to girths above 7' (68 cm dia.).

In 1978 stem analysis was made of 24 teak trees with diameters at breast height ranging from 55 cm to 81 cm in Compartment 16 of Bwet Reserve in Pyay Forest Division. Based on stem analysis data, Kyaw Tint (1980) developed the following regressions to estimate growth in diameter, height and volume of individual teak trees.

A. Diameter growth

i) Age and diameter are related as:

This function is only a rough approximation of the age of a teak tree from its diameter since age-diameter relationships are very variable in natural forests.

ii) Diameter height relationship is expressed by:

iii) Differentiation of d with respect to h gives:

Thus, the relative rate of diameter growth, (dd/dh)/d, is a constant. On transposing (3), we get

which gives diameter increment from interval mid-diameter and the corresponding height increment.

B. Height growth

i) Commutative height growth for individual teak trees is estimated by:

The height growth model develops a system of polymorphic site index curves. If a pair of height-age relationship is available, height can be predicted for any age.

C. Volume growth

The volume and age of the average tree of the 24 trees stem-analyzed are related by the following regression equation:

and its first derivative:

estimates CAI. In these equations:

a = 0.00021,

b = 2.3699,

c = 0.9868,

R² = 0.9959.

According to these regressions, an average tree in a dry upper mixed deciduous forest attains a maximum volume of 4.2 m³ at about the age of 178 years. CAI is maximum at about the age of 62 years with 0.0405 m³. MAI catches up CAI at the age of about 100 years with 0.0305 m³ after which the former overshadows the latter.

D. Bark increment

During the forest inventory conducted in Pyay Forest Division in 1974-75, bark thickness was measured on 1,044 teak trees. These data indicate that the relationship between double bark thickness, B, and d, both measured in cm, can be satisfactorily represented by the function of the form:

B = Ln a + b · Ln d

The instantaneous rate of change of the bark thickness is, therefore,

dB/dd = 0.66265 d^-1

Growth and yield of natural teak stands

Stand growth simulation models are essential tools of decision making at any level of intensity of forest management. It is in this context that numerous attempts at stand modelling have been made. According to Burkhart (1977) these models may be divided into two broad categories: 1) stand level models that use stand values as the basic modelling unit; and 2) tree level models that use individual trees as the basic modelling unit. The techniques used range from hand-computed individual multiple regression equations to predict stand growth and/or yield to a computerized system of complex functions characterising growth phenomenon of individual trees.

Kyaw Tint (1980) developed a stand level model to predict the growth and yield of the natural teak stands in Myanmar. The model predicts growth, mortality and ingrowth, and generates future stand tables from an initial stand table or tree list provided by inventory. Stand tables are presented in 15 6-inch gbh classes with estimates of: number of yield trees, yield volume and current annual volume increment. A number of control functions are used to restrict predictions within reasonable limits.

Increment is dependent on tree size and total and stand basal area, i.e. basal area of teak and all other species in the stand. The increment function is:

GINC = (0.0196 S - 0.0499) × 0.992 ^GBH × G ^-0.227

In metric units, the equation is:

Mortality is dependent on tree size and number. The function derived is:

ASR = 0.987 + 0.012 {1 - e ^{-0.0745 GBH} (1 + 0.0745 GBH + 0.00277 GBH²)}

where ASR = the annual survival rate. Converted to metric units, the function becomes:

where DBH = diameter (cm).

For Recruitment, a predictive equation could not be developed because of lack of data. Instead, the assumption was made that the ratio of the numbers of stems in the two smallest classes would remain constant throughout the iteration phase. The system simulation model was originally programmed in FORTRAN IV, and now it has been transformed into QBASIC. An extract from predictions made of a natural teak stand in the Middle Nawin reserved forest of Pyay Forest Division is given in Table 6 as an example.

Table 6. An extract from simulation of a teak stand per 100 acres, Middle Nawin

In 30 years total growing stock of the teak stand has increased from 499.8 tons to 745.5 tons, i.e. by 245.7 tons. This amounts to a mean annual increment of 4.095 cubic feet per acre per year (0.2865 m³/ha/year) during the predicted period. The maximum current annual increment is 9.1 tons over 100 acres. This is equivalent to 4.55 cubic feet per acre per year (0.3184 m³/ha/year).

Vanclay developed the Spread Sheet Stand Table Projection Model (SSPM) in 1992 to predict growth of natural teak forests in Myanmar. The model predicts growth (diameter increment), deaths and recruitment and assumes parameters for harvesting (removals, defect and damage). SSPM version 1.0 was implemented on Lotus 1-2-3 (release 2.2) and restricted to only two species groups, teak and all other species combined. The enhanced SSPM version 2.2 was implemented on Lotus 1-2-3 (release 3.1) and employed three species groups: teak, pyinkado and all other species. In the new version some financial analyses were also available. In SSPM 1, an annual mortality rate of 0.5% for teak and 1% for all species was assumed while SSPM 1.2 used density dependent mortality. It was assumed that one-way linear equations were adequate.

Diameter increment. Diameter increment was estimated by forest region and expressed as:

DI = Max [0, a + b × BA]

where BA = total standing basal area (m^2/ha).

Recruitment. The number of new recruits to the stand table was estimated by:

Defect and damage

From logging experiment, defect in gross volume of teak harvested and the logging damage (% of stems damaged by size classes), the following relationships were derived:

The model works as follows: Except in the smallest and largest classes, the number of trees in the class N_i at time (t+1) will be:

N_{i, t+1} = (S - R_m) × N_{i, t} + R_m × N_{i-1, t}

In the largest class, there will be no upgrowth. Hence:

N_i, _t+1 = S·N_{i, t} + R_m × N_{i-1, t}

For the smallest class, there will be recruitment, and hence:

N_i, _t+1 = (S - R_m) × N_{i, t} + Max [0, a + b × BA].

The number of trees in the smallest class is controlled.

The SSPM is simple and easy to use, and it poses a wide scope for further improvement. It was initially developed for immediate use for the ForMIS (Forest Management Information System) that the Forest Resources Division was constructing at that time.

A comparison of growth of individual trees

A comparison of growth in breast height diameter of individual natural teak trees in Myanmar, India and Thailand is presented in Diagram 2. Teak trees from India were said to have grown in the good moist forests. Myanmar teak was from the dry upper mixed deciduous forest, while Thailand teak represented an average tree growing in its north.

Diagram 2. A comparison of growth of individual trees

Note: Warangal (India) and Myanmar teak showed better growth rates than those of Hoshangabad (India) and Thailand.

PRODUCTION AND EXPORT OF TEAK

Lao PDR

Felling of teak trees is prohibited at present. Only those logs remaining from past exploitations and from shifting cultivation areas are collected. The annual production has been about 500 m³ (Pengduoang, 1991). Forests of Laos have been managed in recent years to produce a total log output of about 250,000 m³ per year. One estimate is that approximately 10,000 m³ of teak logs were produced annually and mainly exported to Thailand (Pengduoang, 1991).

Thailand

Thailand has completely banned teak logging and concessions since 1983. The period from 1975 to 1979 saw sizable annual productions ranging from 112,000 m³ to 264,000 m³. Starting from 1980, the production gradually declined until it reached the minimum of 26,000 m³ in 1989 (a residual harvest after the logging ban (Rao, 1991). Production of teak timber from 1975 to 1989 is shown in Table 7.

Table 7. Production of teak in Thailand 1975-1989

Source: Y.S. Rao, paper presented at the Regional Seminar on Research and Development of Teak, China 19-28 March, 1991.

Myanmar

Girdling of teak

Teak trees are girdled three years prior to felling. Girdling makes a cut about 5-6 inches wide around the stem as close to the ground as possible through bark and sapwood right into the dark brown hardwood. The girdled tree dries partially and seasons evenly in two or three years. It is a Myanmar traditional practice from time immemorial. The status of teak girdling by the Forest Department and felling by the Myanma Timber Enterprise (MTE) during the last 5 years is presented in Table 8.

Table 8. Status of girdling and felling from 1990/91 to 1994/95

* Provisional actual; ** Provisional.

Source: Review of the Financial, Economic and Social Conditions for 1994 and 1995, Ministry of National Planning and Economic Development, Union of Myanmar.

Note. At the beginning of 1990-91 there were 488,000 trees already girdled.

During the period 652,000 girdled teak trees were extracted, i.e., 183,000 trees more than actually girdled during the period. The excess must have been drawn from old stock. The remaining stock should be checked and future girdling planned accordingly.

Production and export

The status of production and export of teak during the last 5 years is shown in Table 9. As seen in this Table, production of teak logs has been reduced gradually during the period with a view to improving the natural teak stock. On the export side, log export shows an upward trend except for a drop in 1991-92. Although the present policy is to gradually reduce log exports, we still fail to achieve this objective due to lack of investment, infrastructure and technology to go into downstream internal processing. The annual export of sawn timber reached its peak in 1992-93 with 45,850 m³.

Table 9. Production and export of teak from 1990/91 to 1994/95

* Provisional actual; ** Provisional

Source: Review of the Financial, Economic and Social Conditions for 1994 and 1995, Ministry of National Planning and Economic Development, Union of Myanmar.

LOGGING SYSTEMS

Myanmar

The Myanma Timber Enterprise (MTE) holds a monopoly over the extraction and marketing of teak. MTE was constituted in 1952 as the State Timber Board to take charge of forest extraction and forest industries for the State. It employs nearly 50,000 staff and presently operates 38 extraction and rafting agencies.

Stumping and dragging of teak logs to the edges of floating streams are carried out mostly by elephants and on some occasions by oxen and water buffaloes. MTE today own nearly 3,000 elephants and uses about 6,000 for timber harvesting, the balance being hired from the private sector.

Elephant logging causes least damage to the standing trees and environment. Hence bulldozers and other machinery are used mainly for road construction and the loading, unloading and transport of logs. A completely mechanized extraction will not be economically feasible as only about 2-3 trees/ha/cycle are harvested, and the operation would be destructive to the remaining trees and environment under the MSS.

Transport of teak logs in rafts along the rivers has been used in Myanmar since the time of King Badon in about 1789 AD, and is considered to be most convenient and economical. Teak logs are floated down the streams singly and are collected in the main river, made into rafts to be floated down again to the main timber depots in the lower parts of the country. Raft sizes vary from about 200 logs to over 1,000 depending on the size of the floating stream or rivers. Up to recent days, rafts were constructed using large quantities of cane and of dipterocarp poles. Steel cable rafting was introduced widely from 1994-95 to save millions of pieces of cane and timber poles in raft making and to prevent loss of logs in transit (Aung Thinn, 1994).

FUTURE YIELD

The future yield of teak from natural forests in the Region will indeed decline mainly due to the reduction of their extent. Rampant cutting and land conversion to other uses has alarmingly degraded and exhausted natural teak forests. Of the four countries with indigenous teak forests, Myanmar is the only country which still has extensive stretches of natural teak bearing forests; even so, Myanmar also has experienced some degradation and depletion during the last few decades.

India

The moist deciduous and the dry deciduous forests were renowned in the past for the quality of teak they produced, but this is now a thing of the past. Much of the teak forest in the country has been reduced to a sterile bush in the last four decades due to excessive demand and exploitation for meeting local needs (Tewari, 1992).

Lao PDR

In Lao PDR, natural teak forests have suffered a rapid degradation of the growing stock and reduction of area. The extent of these forests is now 16,000 ha, with 10,000 ha in Sayaboung Province and 6,000 ha in Bakeo. Extraction has been confined to the collection of the logs remaining in the past extraction areas and in the clearings for shifting cultivation. The cutting of teak trees is now prohibited (Pengduoang, 1991).

Thailand

As of 1982, natural teak forest in Thailand was about 2.5 million hectares. The teak forests had been so over-cut that logging and concessions have been completely prohibited since 1983. Only residual output continued till 1989 (Kaosa-ard, 1991).

Myanmar

The annual allowable cut (AAC) of natural teak in Myanmar has been prescribed as 603,485 m³ or 178,750 yield trees since the early 1970s. How actual felling compared with the prescribed yield during the period from 1946 to 1994 is seen in Table 10.

Table 10. Prescribed yield and actual fellings from 1946 to 1994 (Number of trees)

A National Forest Inventory was conducted in six Divisions and two States during 1982 to 1988. The potential yields estimated using the inventory data (as 1985 estimates) are shown in Table 11 against the AACs that have been prescribed since early the 1970s. Table 11 demonstrates that the present Allowable Annual Cuts are still safe. Under the Myanmar Selection System overcutting in a forest area is impossible if the prescribed girth limits and girdling instructions are strictly observed. The only adverse thing that can occur is that the Felling Series will be covered in less than 30 years or the yield will drop.

Revision of AAC is now underway. In 1994-95, Bago, Mandalay and Magway Divisions and part of Kachin State were inventoried with this particular objective in view. Data awaits processing.

From 1948 till 1994, a total of 183,000 ha of teak plantations was established. The average annual area of planting has been more than 11,000 ha since 1980. Assuming a rotation of 80 years with a final yield of 300 m³/ha, (a very conservative estimate), and assuming again that only 50% of the plantations remain at the final cut, teak plantations will supplement a yield of about 1.65 million m³ annually at least starting from the year 2059.

Table 11. The potential yields (AAC 1985) compared to the prescribed AAC yield trees of 7' gbh (68 cm dia.) and above

* Authors' estimate

MONITORING AND LONG TERM AVAILABILITY OF RESOURCE DATA

Forest inventory in Myanmar dates back to 1856 when Dr. Brandis applied linear surveys to collect forest statistics in Bago Yoma. However, the use of sampling theory in Forest Inventory was initiated only in 1963. The National Forest Inventory employing a Continuous Forest Inventory (CFI) system started with UNDP/FAO assistance in 1982. It has now covered about 30 million acres (12.1 million ha), mostly of teak bearing forests. So far, 2,450 permanent sample plots (PSPs) have been established on a systematic grid of 6,600 yards (6,600 yards in almost all commercial forests. They are remeasured every 5 years to provide data for continuous monitoring and evaluation of current status and change of the forest resources and also for the development of simulation models.

In addition, since 1922 teak trees of 4' gbh and above (39 cm dbh+) have been completely enumerated during girdling operations. These data are also available for planning and monitoring purposes.

CONCLUSIONS

Beautiful dense natural teak forests in three out of four teak countries have now become a glory of the past. Remarkably this has not been due to the weaknesses of the management system but to the indiscriminate cutting and the lack of, or insufficient appropriate silvicultural treatments, resulting most probably from many constraints beyond the control of the forestry organizations.

It is noted that all the countries with natural teak forests practice selection felling systems. To Myanmar, the selection system seems to be most appropriate for natural teak forest management. Selection needs to be tailored to the specific forest types and the management objectives. Soil, climate, topography and other environmental factors of the site where teak thrives naturally are usually very favourable for tree growth. Predictably, if tending operations are done correctly and timely, together with effective protection of the forests from outside disturbances, sustained development of native teak forests can be ensured.

Conversion of natural teak forests to extensive plantations of teak monoculture could possibly lead to an environmental disaster. Increased productivity of high quality timber can be aimed at by enriching the existing stands with the introduction of genetically improved seedlings in the gaps. Bamboo flowering should be taken advantage of immediately and to the fullest extent possible.

Research and development of wood properties and utilities of lesser known species, growing in association with teak, should be strengthened and intensified so that these can be extracted together with the premier species. This will reduce not only the cost of extraction but also the amount of damage done to the residual teak crop, soil and the environment during extraction.

The destruction of the natural teak forests is a global concern. The issue is not confined only to the countries where these forests exist. It is also a concern to the consumers, the scientists, the geneticists and the environmentalists all over the world. Financially handicapped nations are simply incapable of just conserving and improving the forests. They have to utilize the forest resources for their economic and social development. In this perspective, multidisciplinary, multisectoral and multinational approaches within the framework of TFAP is essential to ensure the sustainable management of natural teak forests for continued supply of quality timber to satisfy the needs of both present and future generations.

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