1. Present situation
1.1 Natural woody vegetation
1.1.1 Description of the vegetation types
Thailand has a variety of vegetation types ranging from tropical evergreen rainforest to dry deciduous forest and savanna forest which reflects the wide range of ecological and climatic conditions. The main types are listed below within the broad classes used in this study. Several documents have been consulted for the compilation of this description such as (3), (6), (16), (28) and (44), and “Tropical Rain Forests of the Far East” by T.C. Whitmore, and (4), (8), (12) and (13) for specific types of forest
Closed broadleaved forests (NHC)
(a) Evergreen and semi-evergreen forests
(i) Tropical evergreen and semi-evergreen forests occur from sea level up to 1 000 m elevation where annual rainfall is at least 2 000 mm and fairly evenly distributed throughout the year. Drier types of evergreen forest are found in areas with a seasonally dry climate. Three subtypes can be distinguished in Thailand:
tropical lowland evergreen rainforests, covering just over 350 000 ha (28), are found only in the far south of the peninsula where the seasonal variation in rainfall is smallest. They have three major tree layers and a sparse ground vegetation. The main tree stratum is very diverse and about 24–36 m high, with emergents and smaller shade-tolerant trees below. Dipterocarps dominate in the emergent stratum, especially of the red meranti group (saya) of which Shorea curtisii is common but also S. leprosula, and S. parvifolia and the famous hardwood takhian chan (Balanocarpus heimii) and the tin pet daeng (Dyera costulata). Bamboos are rare except the climbing species, but palms such as Eugeissona tristis and the shade and moisture loving Areca, Iguanura, Nenga and Pinanga are common. The hurricane of 1961 devastated a large tract of the primary forest. It is also heavily exploited for timber and other forest products;
Semi-evergreen rainforests are found in the remaining parts of the peninsula below 1 000 m and north up to about 11°N, covering 800 000 ha approximately (28), and in the extreme southeastern part of Thailand. Huge emergent trees are rare and the whole canopy tends to be lower. Red merantis are absent but white merantis are abundant, especially Shorea hypochra and on limestone S. roxburghii. The legumes Intsia palembanica and Sindora spp. and the dipterocarps Anisoptera oblonga, Dipterocarpus kerrii and Shorea guiso are also very characteristic (Whitmore). Other predominant species are yang (Dipterocarpus spp.), takhian (Hopea odorata) and other Hopea spp., khai khieo (Parashorea steilata), Artocarpus spp., mang tan (Schima wallichii), wa (Eugenia spp.), Syzygium spp. and Diospyros spp. In southeastern Thailand common species are yang, takhian, krabak (Anisoptera costata), ka pong (Tetrameles nudiflora), ta suea (Amoora spp.) sa thip (Phoebe spp.), Diospyros spp. and many others. In certain localities Dalbergia spp. occur. In the provinces of Chantaburi and Trat, khanun nok (Palaguium obovatum), rong (Garcinia hanburyi) and samrong (Sterculia lychnophora) occur with valuable gutta or fruits;
the dominant form of evergreen forest in Thailand is the dry evergreen forest which covered about 3.9 million ha in 1977 (28). It is found along the western parts of the Tenasserim range from latitudes 11° to 16°N, along the western Phetchabun and Dong Phraya ranges and on the southern edges (Dongrak range) and in the northeast (Nong Khai) of the Khorat plateau, in the southeast and in various places in northern Thailand but mainly east of Phrae and near the Laotian border. Dry evergreen forests typically occur with bamboo and scattered patches of deciduous forest and fire climax Imperata cylindrica grasslands, with also shrubs of Eupatorium. Undergrowth is dense. In northeastern Thailand a few deciduous species occur which shed their leaves in the dry season. Areas formerly cropped are under thick bamboo and thorny shrubs. Typical tree species are Dipterocarpus spp., Hopea spp., Shorea spp., Intsia spp., Anisoptera spp., Dalbergia cochinchinensis, Fagraea cochinchinensis, Cinnamomum spp. and Lagerstroemia spp. There is a dense lower storey composed of a variety of plants including ferms, climbers, palms and, in the open parts, clumps of bamboo (4). In northern Thailand this forest type occurs mostly in moist deeply cut gorges and is often replaced by mixed deciduous forests on the upper slopes. Especially in the north of the Chiang Mai province it covers also large connected areas. Typical trees species there are yang na, (Dipterocarpus alatus), yang pai (D. costatus) and takhian. Among other common are krabak (Anisoptera spp.), yom hom (Toona ciliata), mahat (Artocarpus lakoocha), kra thon (Sandoricum koetjape) and near streams chomphu (Eugenia spp.) and dam dong (Diospyros spp.). The undergrowth consists of various palms such as rattans (Calamus spp.), Arenga saccharifera and bamboos such as mai bong yai (Dendrocalamus brandisii), mai hia (Cephalostachyum viragatum) and mai rai khruea (Dinochloa maclellandii). The forests of central Thailand have a more or less similar composition except that the main bamboo species is mai phai pa (Bambusa arundinacea). Yang na also tends to form more pure stands (1) (3). In southeastern and southern Thailand the dry evergreen forests generally resemble the semi-evergreen forests of these regions except for their generally poorer composition and smaller diameters. Yang na and other Dipterocarpus spp. form the important part of the forest.
(ii) Hill evergreen forests occur above 700 m in areas where rainfall exceeds 1 400 mm and is fairly evenly distributed throughout the year. This type of forest covers 350 000 ha (28) mainly in northern Thailand and on the western edge of the Khorat plateau. Emergents are absent and so there are only two tree layers. Size of the trees decreases with altitude while epiphytes become more abundant. Dominant trees are oaks, (Quercus and Lithocarpus spp.) and chestnuts (Castanopsis spp.) while species of Dipterocarpus and Hopea recede. Common species are thalo (Schima wallichii), kha hot (Engelhardtia spicata), kam yan (Styrax benzoides), champa (Michelia champaca) and others. Species of the Rosaceae, Ericaceae, Magnoliaceae and Lauraceae are well represented.
(iii) Fresh water swamp forests occure in central and southern Thailand, mostly in the peninsular region. They are two storied. In central Thailand the most common species are krabao (Hydnocarpus anthelminticus), chum saeng (Xanthophyllum glaucum), inthanin (Lagerstroemia speciosa, thon (Albizia procera), thong kwao (Butea monosperma) and many Nauclea and Barringtonia spp. In southern Thailand common species are kan krao (Fagrasa fragrans) and Cratozylum arborescens) in the upper storey with in the second storey Elaeocarpus spp., this (Alstonia spathulata), wa (Eugenia spp.), chicknam (Barringtonia acutangula), sok (Saraoa sp.) and many rattan species. On water logged clayey soils near the coasts in eastern and southern Thailand samet (Malaleuca leucadendron) forms almost pure stands with amongst others some Carallia spp. and Dillenia spp.. These forests are of great local importance for wood but are drained and cleared at a fast rate, mainly for wet rice cultivation.
(iv) Mangrove forests occur on the thick muddy tidal flats at the river mouths and along the coast of southern and eastern Thailand. They cover large areas along the western peninsula coast (200 000 ha), but also along the eastern peninsula coast (88 000 ha), in the Chao Phraya delta and along the southeastern coast (28 000 ha). They are two storied, with an upper layer up to 20 m high. Most important mangrove tree growing in the upper storey is Rhizophora apiculata and, to a lesser extent, R. mucronata (both are locally named kongkang), ngon kai (Heritiera littoralis) and Xylocarpus moluccensis. Common species of the lower layer are thua khao (Bruguiera cylindrica), thua dam (B. parviflora), prasak nu (B. sexangula) and prong (Ceriops decandra and C. tagal). Prasak (Bruguiera gymnorrhiza) is a common emergent of up to 40 m in height and 2 m in girth. Other species are ta bun khao (Carapa obovata), ta bun dam (C. moluccensis), samae (Avicennia officinalis and A. marina), lam phu (Sonneratia caseolaris), lam phaen (S. griffithii), fat (Lumnitzera spp.), tatum (Excoecaria agallocha), tin pet (Cerbera spp.), ngon gai and lumpho thale (Intsia retusa). Land inward, where mud has accumulated, dry soils are generally formed which are overgrown with ferns and herbs and can give way to evergreen forest. On the edges of the creeks the palm chak (Nypa fruticans) is common. A major part of the mangroves (54%) are under management for charcoal production. Species most used are Rhizophora apiculata, R. mucronata, Avicennia marina and Xylocarpus.
(v) Beach forests develop on sandy beaches along the coast. Main species of this narrow forest belt are son thale (Casuarina equisetifolia), krathing (Calophyllum inophyllum), yi thale (Pongamia pinnata), hu kwang (Terminalia catappa) and pho thale (Hibiscus tiliaceus).
(b) Deciduous forests
Mixed deciduous forests occur from the plains up to 1 000 m elevation where annual rainfall is between 1 250 and 2 000 mm with well pronounced dry and wet seasons. Fire plays an important role in these forests and often fire resistant tree species such as teak (Tectona grandis) dominate. During the dry season large areas of these forests are burnt. They extended over 4.2 million ha in 1975 (28). Because of the light canopy, undergrowth is dense with many characteristic bamboo species. Three subtypes are distinguished which often occur in a complex mosaic pattern:
lower mixed deciduous forest on sandy loams and lateritic soils 300 m elevation. The forest has three storeys. Teak is absent from the upper storey. This subtype occurs in the northeastern part of northern Thailand and south of the Phetchabun range;
dry upper mixed deciduous forest on sandy loams or gravel soils above 300 m elevation. It extends over a large area along the Tenasserim mountains from 120°30' N up to Mae Hong Song in the extreme northwest and through northern Thailand to the Laotian border. It has mainly deciduous trees and its ground layer is often destroyed by fire. Repeated depletion of these forests turn them into bamboo scrubland;
moist upper mixed deciduous forest on loamy calcareous or granitic soils also above 300 m elevation, occurring in the northern tip of the country and on the eastern and northern edges of the Khorat plateau. Evergreen trees are prominent. The undergrowth is well developed. Palms only occur locally. This type gradually merges into evergreen forests.
Teak which is the main commercial species of Thailand is the dominant tree in the mixed deciduous forests of northern Thailand, except in the lower type and occurs south as far as the Kanburi province. These forests are open with teak trees isolated or in small groups. Sometimes in suitable locations, on alluvial soils, teak forms pure stands. Other common trees in these forests are pradu (Pterocarpus macrocarpus), daeng (Xylia kerrii), tabaek (Lagerstroemia calyculata), salao (L. tomentosa), puei daeng (L. balansae), chok (Schleichera oleosa), makhamong (Afzelia xylocarpa). Dipterocarpus alatus, D. costatus are rare. The undergrowth consists of bamboos such as phai ruak (Thyrsostachys siamensis), mai rai (Gigantochloa albociliata), mai bong (Bambusa tulda), mai sang (Dendrocalamus membranaceus) and others. In the forests without teak pradu is the dominant trees with daeng, tabaek, salao and others. In the undergrowth the bamboos phai ruak and Bambusa arundinacea prevail.
Teak regenerates very well after careful exploitation (contrary to yang species) and is rather fire resistant.
Open broadleaved forests (NHc/NHO)
(a) Dry dipterocarp forests are found on the plains and ridges where soils are poor, generally either sandy or gravelly and subjected to extreme leaching and erosion. Dry dipterocarp forest is dominant in northeastern Thailand where in 1963 it covered 51% of the total forest area of the country (4), but extensive areas also occur in northern part of the central plain and in northern Thailand. They correspond to an annual rainfall below 1 250 mm and a dry season of six months. Most of these forests are subject to annual fires and have an undergrowth of bamboos and grasses. Natural regeneration is usually abundant and the seedlings and saplings survive the fires through an accumulation of flood nutrients in their root stocks. In northern and central Thailand common trees of commercial importance are phluang (Dipterocarpus tuberculatus), hiang (D. obtusifolius). teng (Shorea obtusa) and rang (Pentace siamensis). Hiang prefers more loamy soils. Others of less commercial value are rok fa (Terminalia alata), tabaek lueat (T. mucronata), rak mu (Buchanania latifolia), matum (Strychnos mux-blanda and S. nux-vomica), makham pom (Phyllanthus emblica), yo pa (Morinda tinctoria), mok (Holarrhena antidysenterica), Randia spp. and many species of Dillenia, Quercus and Castanopsis. Undergrowth consists of grasses, the palm Phoenix acualis, Cycas siamensis and shrubs. In northeastern Thailand the common commercial trees are the same as in the Northern and Central regions but other principal species are Shorea floribunda, kwao (Adina cordifolia), ma kha tae (Sindora siamensis), daeng (Xylia kerrii) and pradu, with auxiliary species such as ta khram (Caruga pinnata), phruek (Albizia lebbek), chok (Schleichera oleosa), tabaek na (Lagerstroemia floribunda), oi chang (Lannea coromandelica), Terminalia spp., makham pom (Phyllanthus emblica), sawong (Vitex limonifolia), samae san (Cassia garrettiana) and pui (Careya arborea). Predominant undergrowth is the grasslike bamboo ya phet (Arundinaria ciliata). The composition of the dry dipterocarp forests in eastern Thailand is similar but generally poorly developed.
(b) Savanna forests can be found in small patches of different types scattered all over the country on sandy or lateritic soils but are most frequent in the Northern and Northeastern regions. They originated as a result of the burning of the deciduous forests. The soil is often covered with Imperata cylindrica and other grass species. (6) gives some plant composition for northeastern and southeastern savannas. The first is dominated by Pterocarpus macrocarpus with some Piliostigma malabarica and Gardenia erythroclada. The latter includes mostly Mitragyna javanica with Xylia kerrii, Turpinia pomifera, Careya arborea and others. Extensive savannas may turn into grasslands such as the Thung Kula Rawang Hai swamp in Sakon Nakhon province.
Bamboo forests (NHB)
Bamboos constitute the natural undergrowth in deciduous forests. They are especially favoured by fire and other disturbances and can become the dominant vegetation. As a result of ancient shifting cultivation large areas are covered with bamboos, mainly Oxytenanthera albociliata and O. nigrociliata which like open areas and often follow shifting cultivation, but also mai sang (Dendrocalamus spp.) and mai bong (Bambusa tulda). In the watersheds of the Mae Nam Kwae and Mae Nam Klong rivers in northwestern Thailand they covered 800 000 ha in 1972 (14). They also occur in the Salween drainage in the extreme north all along the Burmese border. These bamboos, which are utilised by the paper industry, are Thyrostachys siamensis and Bambusa arundinacea but in the northern catchment areas of the Kwae and Klong rivers are the giant Dendrocalamus spp. (D. hamiltonii, D. gigantochloa and D. longispathus) and mai bong.
Coniferous forests (NS)
Coniferous forests are found on the sandy soils and red loams of northern and central Thailand and on the Khorat plateau. They usually grow on the peaks and dry steep slopes and replace the dry dipterocarp forests above 700 m up to 1 400 m, although a few stands are also mentioned in the plains and near the coast. In the transitional zones the conifers are often mixed with typical species of the dry dipterocarp forest. On higher elevations associated genera include Quercus, Lithocarpus, Castanopsis, Pieris and Eugenia Two species of conifers occur in these forests: Pinus merkusii and P. kesiya (=P. insularis) of which P. merkusii is the commoner one and is found on lower elevations. Pure stands are indications of the controlling effects of fire. The total area was estimated at 250 000 ha in 1975 (28). In certain localities where forest fires are frequent, the forest becomes a park savanna.
Scrub formations (nH)
Patches of scrub forest occur on the drier eastern side of the peninsula from Chumphon (11°N) northwards in the coastal plain (Whitmore) covering about 140 000 ha
Scrub dry dipterocarp forest is most likely the result of heavy exploitation of ordinary dry dipterocarp forest. It has the same species composition but the trees are much smaller. These scrub forests are heavily exploited for fuelwood and wood for charcoal in northeastern Thailand but also elsewhere. Large areas in northern Thailand formerly covered with shrubs are now completely devastated.
1.1.2 Present situation of the woody vegetation
The estimation of the area still covered by forest is quite complex. Many contradictory figures are given by the various authors. This is often caused by the different methods and the different concepts of forest used. For instance some authors mean by forest the area legally under the responsibility of the Royal Forestry Department. For this study the results of the interpretation of the 1961 serial photographs by M. Naryamet, S. Chemsomboon and B. Klankamsorn, are used as baseline data for the assesment of the areas covered by forest, subsequently corrected to account for the losses of forest, as indicated in the several documents consulted (9) (17) (33).
From 1961 to 1975 the situation of the forest cover may be summarized as follows:
|(in thousand ha)|
|-||area covered by forest (all types) with forest fallow (resulting from shifting cultivation, mostly in the northern region) at end 1961||27 365|
|-||decrease 1961–1975 (village programs, agriculture, occupied logged-over and indisturbed forest land, dams, roads, etc.…) (11) (17) (29)||8 290|
|-||area covered by forest with forest fallow of period 1961–1975 at end 1975||19 075|
|-||area covered by forest without forest fallow at end 1975||18 475|
This gives an annual deforestation rate for 1961–1975 of 2.6%. Various estimates have been made for the annual deforestation rate from 0.5% for the period until 1970 (13), a figure copied in many reports, to 3% (24) and up to 10% (33) for the period 1973 – 1977. Obviously the figures of the late seventies are much higher than those of the early seventies. For this study the annual deforestation rate of 2.6% is used for the period 1976–80, resulting in a total forest area without forest fallow of 16 175 000 ha at the end of 1980 (N.f+NHc/NHO+nH).
The following table provides an estimation of the situation of the woody vegetation cover as at end 1980.
Areas of natural woody vegetation estimated at end 1980
(in thousand ha)
The following comments are necessary for a good understanding of the above figures:
shifting cultivation occupied both the lowlands and the hills. However lowland shifting cultivation areas have been soon utilized for permanent agriculture while a part of shifting cultivation in the hills which often occupies vulnerable watersheds, can still be considered as forest fallow (NHCa). In 1975 forest fallow covered an area of 0.6 million ha (29) (36). The annual increase of the total area affected by shifting cultivation is estimated at 40 000 ha (80 000 families with approximately 450 000 people (7)). The area covered by shifting cultivation, in 1980 can thus be estimated at 0.8 million ha;
according to (13) the evergreen and mixed forests together (NHCf) correspond to 62% of the forest cover, and the dry dipterocarp forests (NHc/NHO) 38%. Swamp forests (in NHCf2i) cover an area of some 400 000 ha (mangroves: 313 000 ha, fresh water swamps: 80 000 ha) (24) (39);
in northern Thailand pine forest (NSf) is found in the Om Koi area where it covers 71 000 ha, in the Bo Luang area with an area between 50 000 and 100 000 ha and in the Kun Yam area covering presumably an area between 15 and 20 000 ha. Pinus merkusii stands account for 91% of the total pine area (8) (14). In the Si Sa Ket province (500 km east of Bangkok) 2 500 ha of pine forests are found. Small pure stands of pine occur also in the Phitsanulok province (central Thailand) with exceptionally large trees of 10–15 m3 each. Other large pine-bearing areas exist in northern Thailand, but they have not been surveyed yet (8). The Phu Kradeung national park includes 35 000 ha of pine (IUCN, List of National Parks and Equivalent Reserves, 2nd edition), i.e. NSf2r=35. Total pine area outside national parks is estimated at 175 000 ha for 1970 and at 165 000 in 1980 (NSf1). Pines are often mixed with broadleaved species in the hill evergreen forests without being dominant and the corresponding stands are included in NHCf;
in 1970 the total area of bamboo forests (NHB) was estimated at 1 million ha (13) of which 400 000 inaccessible (NHBf2i) near the Burmese border and the rest covering the watersheds of the Mae Nam Kwae and Mae Nam Klong rivers (NHBf1) (8) (14). Annual decrease is estimated at 10 000 ha;
in 1980 national parks and equivalent reserves occupy a total area of 2 868 000 ha (1980 UN list of National Parks and Equivalent Reserves) of which 2 185 000 ha are considered to be covered by closed broadleaved forests (NHCf2r), 575 000 ha by open broadleaved forests (NHc/NHO2r) and 35 000 ha by coniferous forests (NSf2r). No exact data are available but half of NHCf2r is considered to be in the watershed protection forests which cover 10% of the total country area (5.2 million ha);
40% of the remaining open broadleaved forests are heavily overcut (NHc/NHOf2i) (1) (4);
scrub forests (nH) cover about 0.5 million ha (12). Part of them result from overexploitation of broadleaved forests as transition to non-forest land. It is considered that their area is not changing significantly.
All forest lands are state owned and encroaching the forests is illegal. However the population explosion and the immigration of people from neighbouring countries have resulted in an enormous occupation of the forest for shifting cultivation and agriculture. Resettlement programmes are planned to allocate to the people deteriorated forest areas suitable for agriculture to grow trees and crops together in agroforestry systems (29) (31) (38)(40)(41)(43).
Legal status and management
In all the national parks, forest utilization is prohibited. The management of the forests of the country is under the responsibility of the Royal Forest Department which draws up working plans for the teak and other forests (41). Through the Forest Conservation Act of 1913 amended in 1949, the government can protect species and decide on harvesting regulations. 200 trees species, the main timber ones are concerned. About 15 million hectares of forests have been constituted into forest reserves. Despite these management regulations it cannot be said that there are forests intensively managed in the meaning of this study (NHCf1m=NSf1m=NHc/NHO1m=0).
The exploitation of Thailand's forests is the responsibility of the Royal Forestry Department. Until now long-term leases for 30 years have been issued for a total area of 19 million ha of non-teak forest. Through the Forest Industry Organisation (FIO), a state owned enterprise, the government controls nearly all the extraction of the mature teak and yang (Dipterocarpus spp.) and is the largest forest concessionaire in Thailand. Since 1977 some of the logging concessions have been taken over by “provincial Forestry Companies” in which FIO has the major share, other shares being owned by sawmillers and the general public (45).
For all the forests a schema for selective cutting is made for a period of thirty years. A minimum diameter limit is fixed for all the species, and the trees have to be marked by the Forestry Department before the actual cutting. However it is reported that illegal removals take place.
The official figures for timber output as given by the Statistics and Report Section of the Royal Forest Department and the FAO Yearbook of Forest Products are as follows (41):
Production of roundwood (1960–1979)
(in thousand ha)
Since 1977 all forest operations in the border areas, covering 12 million ha, have been stopped for security reasons.
Royal Decree No. 33 bans all export of teak and other valuable logs since 1973. A further ban was declared in 1977 on exports of logs and rough-sawn timber, in order to stop illegal logging and promote export of finished products (32) (41).
The main timber species are teak, yang (mostly Dipterocarpus alatus), Shorea spp., pradu (Pterocarpus spp.) yom hom (Toona ciliata), lumpho (Intsia palembanica), khai khieo (Parashorea stellata), takhian (Hopea spp.), khiam (Cotylelobium melanoxylum), phayung (Dalbergia cochinchinensis), chingchen (D. oliveri), phut (Gardenia collinsae) kaphong (Aglaia pirifera) and other ((23) and others). The exploitation is selective. The average output is 35 m3 for evergreen and semi-evergreen forest, 80 m3 for dry mixed deciduous with teak and 45 m3 for those without teak, 20 m3 for dry dipterocarp forest ((1),(2),(4),(41), “Forest Resources in the Asia and the Far East Region”, FAO 1976). Loss is estimated at 40% during the extraction (11)(41).
Other forests products
Fuelwood and charcoal are the major forest products with an estimated consumption for 1970 of 44.9 million m3 in the households and 3.7 million m3 for industrial use; of this approximately 21 million m3 was removed from the forests (13), although recorded quantities only amount to 1.5–2 million m3 (41). The FAO Yearbook of Forests Products gives an annual average production of 15.5 million m3 for the 1968–1978 period. The proportion of fuelwood used in form of charcoal was in 1970 40% in rural and 45% in urban areas (13). Within the forest areas fuelwood forests and multiple use forests have been set aside: 3.2 million ha for rural consumption, 1 million ha for industrial fuelwood and 0.7 million ha for the railways (29). Industrial uses are for tobacco curing and for paper industry. Many of the logged-over forests and deciduous forests are used for fuelwood production, and these forests are thus deprived of the upgrowth of the commercial species, especially teak.
The mangrove forests are mainly utilised for the production of charcoal for which they supply 1 million m3 of fuelwood annually corresponding to 150 000 tons of charcoal (39).
A number of other products are collected from the forests of which the most important are:
yang oil: the production is presently decreasing: annual average production for 1962–1970 was 4.93 million litres and for 1971–1975 3.05 million litres with a value of 33 million baht (=US$ 1.6 million);
gum damar, with an annual production of 2 666 tons for 1962–1975 and 407.7 tons for 1971–1975 with a value of 2.3 million baht (=US$ 110 000);
bamboo, with an annual recorded production of 30.8 million stems for 1962–1970 and 59.1 million stems for 1971–1975 with a value of 1.2 million baht (=US$ 58 000). Small culm bamboo (Thyrsostachys siamensis) is used for paper making in the Kanchanaburi paper mill, while big culm bamboo (Bambusa arundinacea) is used mostly for building and other construction purposes, particularly in and around Bangkok (8). Bamboo shoots are collected for canning and export (14);
other forest produce are canes, resin, cutch, honey, camphor, etc.
Annual value of all forest products excluding timber amounts to 600–650 million baht (=US$ 28.9 million - 31.3 million) (41).
1.1.3 Present situation of the growing stock
Many figures are available for the growing stock of the various forest formations of Thailand, but they differ considerably. Concerning the evergreen and semi-evergreen forests the results of the forest inventories of the Northern (1) and Northeastern (4) regions were used together with those for the “average” evergreen forest of southern Thailand given in (11). This latter study gives a figure of 87 m3/ha under bark above 12 cm DBH. This figure diverges from those of the forests of Surat Thani province in southern Thailand (140 m3/ha) (22) and those of Peninsular Malaysia (146 m3/ha) (Malaysia national forest inventory, 1970–1972). However this difference can be explained as the study in (11) includes also poorly stocked areas. The weighted average has been converted to VOB volume using 0.75 as a ratio between volume above 30 cm DBH and volume above 10 cm DBH and 0.92 between volumes under bark and over bark. The results of the second national forest inventory (9) were used to weigh each vegetation type in the final VOB figures.
Growing stock estimated at end 1980
(totals in million m3)
For the dry dipterocarp forests (NHc/NH01) the percentages, given by (1) and (4) are used for the respectively “high” and “exploited” forest.
For the swamp and mangrove forests Peninsular Malaysia data are used (Malaysia national forest inventory 1970–1972) as well as those given in (39). The swamp forests contain a volume of 52 m3/ha for trees more than 30 cm DBH, with bark, which corresponds to a VOB of 75 m3/ha. The mangrove forests are reported to have an annual growth for poles of 2.8 m3/ha. The weighted figure of VOB for NHCf2 (including NHCf2i and NHCf2r) is 80 m3/ha.
For coniferous forests many reports quote 45 m3/ha as volume under bark for trees above 30 cm DBH corresponding to a VOB tentatively estimated at 60 m3/ha.
The bamboo forests in the west which cover over 850 000 ha contain an average of 12.7 ton per ha (8). In the Surat Thani forests, in southern Thailand, the best bamboo forests have a volume of over 1 000 m3 per hectare (8).
Volume increment figures of natural forests are scarce. (45) gives as a crude estimate a mean annual increment of about 2.5 m3/ha/year of firewood in dry dipterocarp forest in the Mae Sa area.
Although the first forest plantations (teak) had been established in 1898 and 1906, it was only after 1960 that planting became significant, with an annual planted area fixed by the Royal Forest Department at 800 ha for teak and 1 200 for other species (41). The FAO Timber Trend Study of 1972 (19) called for the establishment of more plantations because of the depletion of the natural forests and the consequent shortage of sawlogs and fuelwood. It recommended an annual planting programme consisting of 46 000 ha of timber plantations and between 18 000 ha (in 1976) and 93 000 ha (in 2000) of plantations for production of fuelwood and pulpwood. A World Bank report (1980) suggest an annual planting of 50 000 ha of multipurpose plantations.
The Forest Department has a certain number of seed orchands and 32 large nursery centres. Planting is concentrated in the Northern and Northeastern regions where also the Teak Improvement Center and the Thai-Danish Pine Project are located. Planting is mainly carried out by special teams of the Royal Forest Department. The Forest Industries Organisation (FIO) is also planting, using the taungya system whereby local people take care for all the planting for a certain payment but also raise agricultural crops such as paddy, maize and others up to 5 years. The people involved are the shifting cultivators who are grouped in a forest village with up to 100 families as one afforestation unit. At the moment there are 35 units distributed in the north, northeast, west and south, each of which are supposed to plant 160 ha annually, with a rotation cycle of 60 years. One of the major problems is the non-availability of logged-over forest land, due to shifting cultivation (31) (38). On a limited scale the Royal Forest Department through FIO uses forest tree crops in alternate rows with rubber. Rotation is fixed at 30 years.
The main hardwood species used is teak. Other species are Pterocarpus macrocarpus, Dipterocarpus and others, but they do not cover extensive areas. Mahogany (Swietenia macrophylla) is planted in the south (10)(16). In Bo Luang (Northern region) the main species used is Pinus kesiya with 26 000 ha planted up to 1973 (19)(20). Elsewhere Pinus merkusii is also used (41). Other pine species have been used on an experimental scale by the Pine Project. Quick-growing hardwood species are planted such Acacia spp. (mainly A. catechu) for fuelwood, Casuarina spp. (mostly C. junghuhniana and C. equisetifolia) for poles and Eucalyptus spp. (“Forest Resources of the Asia and Far East Region”, FAO). Planting is scattered in small patches. Plantation establishement does not seem at present to be planned in relation to predicted demand from industry and households (32).
1.2.2 Areas of established plantations
In the following tables an attempt is made to consider the rather contradictory statistics on areas covered by plantations of the different types, as given by (8),(11),(13), (17),(29),(32),(42) and “Forest Resources of the Asia and Far East Region” (FAO). Several reports mention the fact that only a part of the plantations are successful. The success/survival rate is particularly low for the older plantations. Figures range from 80% of success/survival rate for the teak and as little as 30% for all the rest, to not more than 10% effective (32). Some plantations are destroyed by shifting cultivation. Both the theoretical cumulated areas and the estimated values of successfully planted ares (indicated between parenthesis) are given in the following tables.
Areas of established industrial plantations estimated at end 1980
(in thousand ha)
|PH.1=PHL 1||Tectona grandis and others||30 |
|P..1||Total industrial plantations||32 |
Areas of established non-industrial plantations estimated at end 1980
(in thousand ha)
|P..2=PH.2=PHH 2||Acacia spp.|
Areas of established plantations estimated at end 1980
(in thousand ha)
|PHL(=PHL1)||Hardwood species other than fast-growing ones||30 |
|PHH(=PHH2)||Fast-growing hardwood species||120 |
|PH||Subtotal hardwood plantations||150 |
|PS(=PS.1)||Subtotal softwood plantations||2 |
|P||Total all plantations||152 |
1.2.3 Plantation characteristics
Teak planting is usually done with spacing 2 × 2m. Staking is necessary for stump planting. Planting takes place as soon as the rainy season commences. In the taungya system the traditional spacing of 2 × 2m has been changed to 4 × 4m to facilitate cropping (41). Generally the rate of success in the taungya system is higher (up to 90%) (10). Casuarina equisetifolia is planted at 3 × 4m, 4 × 4m and 3 × 6m. It is reported to grow by as much as 2 m per year during the first 12 to 15 years (5).
Documents (19) and (20) give for Pinus kesiya, with a 2m × 2m, spacing an average height increment of 1 m/year, and a mean annual increment of about 10–12 m3/ha/year for a rotation less than 15 years. In Chang Mai Pinus kesiya reaches far greater height increments.
2. Present trends
2.1 Natural woody vegetation
All studies on deforestation in Thailand agree that the forests are disappearing very fast (see 1.1.2). Permanent and shifting cultivation are by far the main factors of forest depletion. The political unrest in the neighbouring countries made many refugees entering Thailand which had her own population already increasing at a very fast rate. Many of these people together with the hill tribes practise shifting cultivation. More than one million families depend on forested areas for their subsistence agriculture. One family annually needs 1.6 ha of forest of which approximately one third is from the virgin forests (16) (34). Shifting cultivation originally was practised only by the hill tribes in some provinces in the Northern and Central regions (16). But now on many places the primary forest has disappeared and a fire climax vegetation such as open dipterocarp woodland or Imperata cylindrica grassland has developed and is maintained by fires. The total area covered by pure Imperata, often in small patches, is said to be more than 2 million ha (25) (33) (35).. Above 800 m altitude in the north 70% of the forests are lost (26). The deforestation rates are summarized in the following table. Where there is logging, shifting cultivation follows fairly rapidly, in such a way that it can be considered that there is never a significant area of logged-over forests (N.f1uc): in other words the deforestation rates in this category are approximately equal to the areas of undisturbed forests logged-over during the corresponding period.
Average annual deforestation
(in thousand ha)
A study of the uplands north of Chiang Mai indicates that during the dry season all the savannas are burnt but some tribes (especially Karen) use to control fires by breaks. Main crops are poppy (above 1 000 m), paddy and maize. But other important crops are tea and fruit trees. In the same area when during 1960–1972 tea was much in demand planting increased strongly and covered nearly 10% of the area. There was an annual overall loss of 2.72% with the heaviest burden in the hill evergreen and mixed deciduous forests with teak (26) (30) (35). Concerning these estimates and the impact of tea growing on the forests of northern Thailand, (45) makes the following comments: “These figures refer to a relatively small area around Doi Chiang Dao, which is the only area in northern Thailand where potable tea (as opposed to fermented tea for chewing) is grown on even a moderately large scale, and should not be extrapolated. It is unlikely that much is grown in mixed deciduous forest with teak, as this type of forest grows at a lower altitude than is generally suitable for tea…. Growing tea for chewing (“miang”) is an old established practice in northern Thailand, but the practice is to plant the miang under the shade of existing forest, and the main cause of forest destruction is cutting the trees for firewood to cook the miang, rather than the plantations per se. I know of no accurate figures for the total area under miang. In 1964 it was estimated that 75 000 people were occupied in growing miang in Chiang Mai province, which is the main centre of activity. Allowing for population increase, and areas outside Chiang Mai, it is unlikely that the present miang cultivators exceed 150 000, with an average area of 0.45 ha per head, giving a total of between 60 000 and 70 000 ha. In the Mae Sa project area of 420 km2 there are about 190 ha claimed by miang cultivators, though not all of this has actually been planted. The demand for miang is dropping, and a great increase in the area seems unlikely”.
In the Sukothai plain in central Thailand a study on the dynamics of about 1 million ha of land mentions a “pioneer front of settlers” which slowly moves and seriously endangers large areas. There the natural areas decreased from 44% in 1953 to 24% in 1968. The stable areas were those with natural limits or the inaccessible ones (15) (16).
A study of 1978 in an area of 30 000 ha in northern Thailand (35) gives, from 1962 to 1972, an increase of 265% of shifting cultivation but predicts a future decrease through shortage of accessible land. Biggest losses are also here in teak and hill evergreen forests.
This destruction of the valuable watersheds effects the runoff and causes excessive floodings and erosion (1) (4). A major flooding in 1979 of the Pa Kah river claimed 42 lives and damaged agricultural areas (43). Measurements of the run-off and peak flood of the Chao Phraya river for the period 1905–1955 indicated an increase of 15% of the runoff of the peak floods caused by the increasing deforestation. So the precipitation of the monsoon rains cannot be kept in the forests as long as in previous times and villages along the rivers had to be abandoned (23). Also siltation of reservoirs becomes a serious problem. In the Bhumipol dam reservoir, after 8 years of operation, the sediment accumulation was already 1.3% of the capacity, reducing its lifetime from to 800 to 400 years (42).
Forests in the Northeastern region are decreasing by about 3.5% annually due to cultivation. Often the forest canopy initially is felt and only the ground cover cleared for agriculture; but gradually the forest dies (7).
In the northern region, not only the hill evergreen forest but also the teakbearing forest is under heavy pressure; of the original 4.5 million ha from the beginning of the century only 2 million ha remained in 1958 (1). Certain types of bamboo forests are favoured for cultivation. The Thai name for Gigantochloa albociliata (“mai rai”) means the bamboo associated with dru land cultivation (45).
Largest pressure is on the forest in the Eastern region because of its situation close to Bangkok and the ocean, which has resulted in an increased industrialization and, in turn, increased shifting cultivation (2) (7). A study by the Royal Forest Department gives an annual decrease of 5.3% during the period 1973–1976 (27).
In southern Thailand large parts of the forests are transferred into rubber plantation, also on very steep slopes, resulting in a wash out of soils (2). In 1963 there were 450 000 ha of rubber plantations, and this area is annually increasing by 5% (5). Opencast mining of ore deposits, especially tin, also caused a decrease in forest. The hurricane of 1963 destroyed nearly 200 000 large trees in southern Thailand (11). The only remaining areas of mangrove forests outside the forestry reserves occur on very remote places (32).
The most serious degradation of the forests is caused by fire and fuelwood collection especially near the villages and towns. This latter activity affects seriously the dry dipterocarp and mixed deciduous forests. Yearly removal of forest produce, mainly fuelwood, is calculated at 10 million m3 in the Northeastern region while the increment is only 4.5 million m3 (17) (24). Many of the villages are situated close to the dry dipterocarp forests and depend on it for fuelwood (4). Only small parts of climax high dry dipterocarp forest remain (4). 60% of the teak was illegally felled in the mid-fifties and more than half of it was affecting young growth resulting, in 1957, in a mature teak stock of only 28% of the expected stock (1). The situation has not improved much since.
Various degradation factors are affecting also pine forests. In addition to the destructive tapping for resin (8) (14), the main cause of depletion of the growing stock is the collection of resinous chips of pine wood used in lighting charcoal stoves. To stimulate the resin flow a fire is lit at the base of the tree which chars or partly burns the lower stem, from which the resinous chips are then chopped out with an axe. This is repeated until the tree is largely cut through, and breaks off in the next strong wind. A similar method used to collect yang oil causes considerable damage to Dipterocarpus trees (45).
2.1.3 Trends in forest utilisation
Timber output increased from 1.6 million m3 in 1957 to 3.4 million m3 in 1977 and then has fallen to 1.8 million m3 in 1979. Reasons are a degradation of the forest stock and the close of forest blocks along the borders. Utilisation for fuelwood will increase with the population but probably at a lesser rate as increases in price may result in a decrease in consumption per capita.
2.1.4 Areas and growing stock at end 1985
The availability of forests suitable for agriculture will decrease since all the best areas have been occupied already for agriculture. This leads to a decrease in the annual rate of deforestation which for the period 1981–1985 has been estimated at 2.4% of the total forest area left. The projections for the areas and growing stock at end 1985 thus are as follows:
Areas of natural woody vegetation estimated at end 1985
(in thousand ha)
Growing stock estimated at end 1985
(totals in million m3)