J.P. Lanly and Y.S. Rao
The important depletion and degradation of forest cover in tropical zones is having serious effects on the production of forest goods and services and calls more than ever for forest resources monitoring programmes at national, regional and global levels. At national level responsibility rests with the countries themselves, while at regional and global levels specialised international organizations have to take the initiative so that governments and the international community can be made aware of the trends affecting the world's forests. For this reason, at the end of 1978, following the recommendation of the Stockholm Conference, FAO and UNEP undertook a joint programme of forest resources assessment within the framework of the Global Environment Monitoring System (GEMS).
In accordance with its mandate FAO has carried out forest resources assessment at regional and global levels for more than 30 years, publishing the results of its first global survey in 1948. Following this, the 6th FAO Conference (1951) stipulated that this organization should collect and publish information available on the world's forest resources at 5-year intervals. The three versions of the World Forest Inventory were subsequently published for the years 1953, 1958 and 1963, from the compilation of questionnaires filled in by national forestry institutions. For various reasons, related mainly to the diversity of concepts and classifications used by the various countries, the general lack of reliability of the statistics provided and to the fact that these were not always up to date, this approach was replaced by the preparation of regional assessment from documents collected for this purpose. Two of these, entitled “Forest Resources of Africa” by R. Persson (1975) 1 and “Forest Resources in the Asia and Far East” (1976), are related to tropical regions. On the occasion of the 4th session of the FAO Committee on Forest Development in the Tropics (1976) an “assessment of the world's tropical forests” was attempted by A. Sommer and published in the double issue no. 112–113 (volume 28) of Unasylva (1976). More recently for the needs of a world timber trend study, FAO undertook a quick reassessment of the situation and likely trends of forest resources of most developing countries (almost all tropical). A part of the results of this study was published in the document “Present and Future Forest and Plantation Areas in the Tropics” by J.P. Lanly and J. Clément (1979).
As far as we know, there does not appear to be systematic studies on tropical forest resources at regional or global levels other than those carried out by FAO. The “Weltforstatlas” published by the Federal Forest Research Institute of Reinbek (F.R.G.) represents an important cartographic work but does not reflect the present situation of the tropical forest cover, as it was published for the most part between 1955 and 1972. Publications of regional and global maps do exist, such as Hueck's phytogeographic map for South America and the maps made under the auspices of Unesco for South America (by the “Institut de la Carte Internationale du Tapis Végétal” - Toulouse) and for Africa South of Sahara (by Professor F. White - Oxford). Global estimates have been attempted here and there, to support theories or opinions on various subjects (deforestation, global carbon budget, energy sources) but these are generally too superficial, being based on insufficient documentation and questionable extrapolations.
1 Although published outside FAO, this study was initiated and partly carried out in the FAO Forestry Departments.
The objectives described in the project document signed by FAO and UNEP are the following:
long-term objective: to assist the world community to formulate appropriate measures to avoid the potentially disastrous effects of the trends in the depletion and degradation of tropical forest cover. It relates to programme goals D (Assessment of the critical problems arising from agriculture and land-use) and E (Assessment of the response of terrestrial ecosystems to environmental stress) assigned to the Global Environmental Monitoring System by the 1974 Intergovernmental meeting, for which tropical forest cover monitoring activities have already been initiated by UNEP in cooperation with FAO;
to assess, at regional and global levels, the present state of tropical forests and woodlands and the rate and pattern of their depletion and degradation, as a prerequisite for the definition and implementation of the appropriate measures referred to in the long-term objective;
to determine the methodology and the means needed for the continuous updating of this first assessment.
3.1 Preliminary phase
The work started with a preliminary phase for the definition of the methodology and the general programming of the activities during the few months preceding the official starting date of the project (1st December 1978). At the end of 1978 its main methodological features and general planning had been defined. This preparatory phase was made easier thanks to the experience gained during a forest resources assessment study, carried out in 1978 under the responsibility of the project coordinator and already mentioned in section 1. This first study was most useful in many respects:
some principles of classification of natural vegetation and forest plantations had already been defined;
part of the most useful documentation had already been selected and studied;
a first estimate of areas of forests and industrial plantations as well as the order of magnitude of the effects of deforestation and afforestation were already available with an indication of levels of production and productive potential in terms of industrial wood;
the study had allowed the classification of countries with respect to the reliability and completeness of available information on forest resources. This was particularly useful for planning project activities and facilitated the selection of countries where an interpretation of satellite imagery would be needed.
3.2 Working phases
Four main working phases can be singled out for each tropical region, the work for each of which started at three-month intervals in the following chronological order: America, Africa and Asia. The three working programmes have overlapped over almost the whole period of the project which ended in June 1981 with the drafting of the last report.
The study of the 16 tropical Asian countries was carried out as follows:
data collection phase (January–December 1979) including:
visit to some research institutes in Europe, in particular those specialised in the study and mapping of the vegetation;
visit to national institutions in forestry, landuse and surveys in India, Indonesia and Thailand, three countries particularly important for their forest resources; the mission to Thailand also allowed for the collection in the FAO Regional Office of information concerning various countries of tropical Asia;
selection and ordering of satellite imagery for the interpretation of vegetation cover for the whole of Burma and Viet Nam and selected areas of India (Orissa and northeastern states), Kampuchea and Lao;
initiation of correspondence with all the Asian countries concerned, including the mailing of a simple questionnaire and the return by the countries of useful documents on forest resources;
finalization of contracts: (i) with the Indian Preinvestment Survey of Forest Resources (Dehra-Dun) for a “Quick Reappraisal of the Indian Forest Resources” including collection, compilation and interpretation of forest statistics at forest division or civil district level for presentation at state level for the whole of the country and correction and supplementation of the above statistics for Orissa and the states of the northeastern region from interpretation of Landsat satellite imagery; (ii) with the Burmese Forest Department for a “Quick Reappraisal of the Forest Cover of Burma by Using Landsat Satellite Imagery and Other Documents”, including the same two main activities as for the study of Indian forest resources;
interpretation and compilation phase (January–December 1980) including:
visual interpretation of satellite imagery for Viet Nam and selected parts of Lao and Kampuchea;
qualitative and quantitative assessment of the present situation and trends of forest resources country by country, from all the data collected (as well as the results of satellite imagery interpretation for the Indochina countries), using the same concepts and classifications for all the countries. This phase of the work ended with the first drafting of a brief for each country;
completion of the two contracts with the Indian Preinvestment Survey of Forest Resources and the Burmese Forest Department; the final report of these two studies took the form of country briefs similar to those drafted for the 14 other countries;
checking of the first results by the national forestry institutions (January–March 1981): the drafts of the country briefs were sent for comments to the forestry institutions of the respective countries;
drafting of a final report (April–May 1981) including:
the final version of the 18 country briefs (3 for Malaysia: Peninsular Malaysia, Sabah and Sarawak) after they had been corrected to reflect the comments received (part II of this report);
recapitulation at regional level of all final results;
regional overview (chapter III of the first part of this report).
As a whole the work for tropical Asia required 27 months of professional staff, distributed as follows:
8 months of the coordinator and forest resources expert of the project;
2.5 months of the FAO forest resources surveys officer;
1.5 month of the remote sensing consultant;
5 months of consultants (work on some countries);
1 month of the forest economist of the FAO Regional Office for Asia and Pacific (regional overview);
9 months of professional staff of the Indian Preinvestment Survey of Forest Resources and the Burmese Forest Department (estimation).
A fondamental precept in the formulation of the methodology of this study has been that qualitative and quantitative information on tropical forest resources is at the same time abundant, scattered and diverse. Each of these qualifications requires consideration The first one may appear paradoxical: many persons indeed think that relevant information is scarce. However if they had enough time to search for it, they would find, on the contrary, that it exists in abundance.
The main reason why these data are difficult to obtain relates to the second aspect mentioned, that is their dispersion. There are data not only in the national and international forestry organizations but also in a large number of institutes such as survey departments (and remote sensing centres), agricultural statistics services, colonisation and landuse institutes, universities and research organizations in the concerned countries or in developed countries, consulting firms, etc. In this respect many thematic mapping studies were carried out at regional, national and subnational levels, in the 70's thanks to the use of remote sensing techniques (Landsat satellite and side looking airbone radar imagery, small-scale serial photographs). The following examples can be quoted as among the most important in tropical Asia: vegetation, land-use and deforestation maps in Thailand, vegetation map at 1/1 000 000 of the lower Mekong area by the Committee for Coordination of Investigations of the Lower Mekong Basin, the “Landsat assisted forest inventory” for the Philippines, various forest and vegetation maps at 1/1 000 000 of the outer islands of Indonesia (particularly Sumatra, Kalimantan and Sulawesi), etc. Within the framework of this project a certain number of institutions were visited, discussions were held with experts and important correspondence was maintained with many others. It has not been possible, of course, to visit or contact the very large number of national institutions which could have been in a position to provide some useful information, in order to resolve contradictions in the available data, and correct erroneous interpretations found in the documents. It is important, however, to underline the fact that a large part of the project activities consisted of collecting as many as possible of the relevant data scattered around the world.
The third characteristic of this wealth of information, is its diversity which can be inspected from at least three different angles:
with regard to the subject matter, which is often not only restricted to forestry: data concerning deforestation are mainly of socio-economic character (distribution and growth of agricultural population, types and pattern of cultivation, internal population migrations, fiscal and other incentives for forest clearing, colonisation programmes, development of infrastructure and improvement of accessibility, etc). Phytogeographic and ecological information and maps are also of essential importance to classify forests according to their production potential. Laws and regulations in the field of natural conservation, indicate the forest areas unproductive for legal reasons, etc.;
with regard to the level or scale of information: it is easier to bring forest resource data up-to-date when forest inventories, reconnaissance surveys and maps have been carried out at national or subnational levels. However, a large amount of information can be found in studies at lower levels (province, district, investment zone, watershed). Although, in many instances, a simple quantitative extrapolation is not feasible, these data are always useful to check corresponding information at national level, to compare situations from one country to the other, or, at least, provide examples to illustrate particular situations and issues (deforestation, degradation, survival and success of plantations, etc). These local studies are the most numerous and contain the largest amount of useful information. For example many forest inventories have been carried out by the Indian Preinvestment Survey of Forest Resources: the resources assessment specialists of this institute who participated in this project spent part of their time collecting the results of these numerous inventories to assess the forest resources situation at national level. Local studies of this type are often not easily retrievable because they have been published in a very small number of copies and are not quoted in most bibliographies (University theses for instance), or because they are not known by foresters since they do not deal strictly with forestry matters (studies on sociology, population, agriculture, etc.);
lastly, with regard to the reliability and accuracy of data: all documents on forest resources are obviously of different value and there are many crude assessments and dangerous extrapolations which must be considered with caution. Often obsolete information is used again and again in documents, disregarding changes which have occurred in the meantime. It is of the utmost importance to trace out these deficiencies in the data, by means of checks against other sources.
This study has consisted mainly in the selection, organization, compilation and interpretation of this abundant and diverse mass of information using a single framework of classification and concepts for the 76 tropical countries studied (see section 2). However, in some countries, reliable base-line data on the areas of woody vegetation which could have been used for subsequent up-dating, did not exist at national level. In other countries the project was confronted with two or more sets of area information which could not be matched. In these cases it was decided to interpret available satellite imagery (of the years 1972–1978) to check and possibly correct areas estimates obtained in a first phase (see section 3). For all countries it has been necessary to up-date the information at the end of 1980 on the basis of the trends observed in the last years and to project the situation at the end of 1985, on the basis of an estimation of the trends in the next 5 years (see section 4).
The value and usefulness of any forest resources assessment study depends, to a large part, on the concepts and classifications used. These must have several characteristics which are not necessarily compatible. In particular they must be:
in accordance with the study objectives;
defined with precision and without ambiguity;
adapted to the type of items surveyed;
matched as closely as possible to the needs of the most important users;
compatible with concepts and classifications already in use in tropics;
and, last but not least, applied uniformly to the three main tropical regions in order to obtain a consistent picture of the whole tropical world.
In addition to the above conditions, the concepts and classifications of the study must be compatible with those already used in the former FAO World Forest Inventory reports for purposes of comparison and consistency. All these conditions can be fulfilled if one adopts forestry concepts currently in use and classifications which are not too detailed.
2.1 Concepts and classifications of natural woody vegetation
2.1.1 A large number of systems of tropical vegetation classification already exist, using various criteria (ecological, physiognomic, physiographic) at both national and regional levels. In this latter category the following classifications can be identified for tropical Asia:
the Champion's classification of the forest vegetation of the Indian subcontinent outlined in “A Preliminary Survey of the Forest Types of India and Burma” (1935) and amended in “A Revised Survey of the Forest Types of India” by H.G. Champion and S.K. Seth;
the classification by C.G.G.J. von Steenis in its “Vegetation Map of Malaysia” at 1/5 000 000 covering Malaysia, Indonesia, Philippines and Papua New Guinea published in 1958 in collaboration with Unesco;
the classification by J. Schmithüsen in his “Atlas zur Biogeographie” covering the whole world.
Vegetation classifications at national level are many. They have been used in this study for those countries where there was a corresponding map. As it has already been mentioned in chapter I a new generation of vegetation classifications and maps has emerged in the last ten years using classification based on the interpretation of satellite and radar imagery. Classification criteria and categories differ widely not only from one country to another but also within the same country.
2.1.2 When deciding on the forest vegetation classification to be used in this study; great care has been exercised to make it compatible with the Unesco one (in series “Ecology and conservation no. 6 "International Classification and Mapping of Vegetation”) because of the useful aspects of this latter i.e.:
it applies to the whole world while most of the others are limited to one region only;
it is possibly the first collective and international attempt at a global vegetation classification (while each of the others have been elaborated by a single specialist or a national institute);
it contains a certain number of most important distinctions for forest resources management, such as: separation between tree ans shrub formations, separation between more or less closed tree formations on one side and grasslands with a tree synusia on the other side. This latter distinction is essential in tropical countries since the mixed forest-grassland formations play a most important role for grazing and are prone to fires.
2.1.3 In addition to the distinctions mentioned above (tree/shrub and closed forest/mixed forest-grassland formation) there exists other essential classification criteria for woody vegetation formations both from the productive and environmental viewpoints, such as:
distinction between predominantly broadleaved forests and predominantly coniferous forests;
separation between forests which have not been disturbed recently (virgin or primary) and manipulated forests: forests clearfelled and later on provisionally abandoned by shifting cultivation (“forest fallow”), forests degraded by overgrazing and fire, logged over forests;
distinction between productive and unproductive forests using the criterion of industrial wood production, and separation of these latter between those which are unproductive for physical reasons and those which are so for legal reasons (national parks, integral reserves).
The simultaneous use of all these criteria provides a large number of classes. Some of these classes are not important. Others cannot be identified from the interpreted documents and images and their areas and characteristics cannot therefore be determined. The classification which has been finally adopted is limited to the most useful categories. The following chart presents this classification with the corresponding criteria. The various categories are described in detail below.
2.1.4 Classification of natural woody vegetation (N/n)
The only vegetation types which are considered are those for which woody elements cover more than 10% of the ground. Though it is often difficult if not impossible to estimate this percentage from the descriptions and this percentage is not always used in the classifications, it has been selected as the limit between the types in which the woody elements constitute actually a community and those where they are scattered or (in lines) in landscapes with a non-woody vegetation or without any other vegetation.
The word “woody” is used although the trees of some monocotyledons do not contain “wood” in the usual meaning of the word.
The adjective “natural” is used only in relation with plantations which can be considered as a purely artificial vegetation (see below section 2.2). This does not mean at all that there is no human or, more generally, biotic interference. On the contrary, a significant proportion varying with countries of “natural vegetation” corresponds indeed to degradation stages (after fires, clearings by shifting cultivation, overexploitation for wood, grazing) or reconstitution stages after degradation, or to forests disturbed by logging, with or without management.
N stands for any vegetation type of which the dominant woody element is the tree. The definition of a tree is the one given by the book “Terminology of Forest Science, Technology, Practice and Products”, viz. “a woody perennial plant typically large and with a single well defined stem carrying a more or less definite crown” (height more than 7 metres for mature trees).
n corresponds to any vegetation type the main woody elements of which are shrubs of more than 50 cm and less than 7 metres high 1.
NH corresponds to types with predominance of trees of broadleaved species (angiosperms) dicotyledons or monocotyledons (e.g. palms, rattans). Predominance is characterised by a proportion of more than 50% of the crown cover.
NS corresponds to types with predominance of trees of coniferous species (gymnosperms). Coniferous species for instance of genus Podocarpus are often present in mixed tropical forests of medium and high mountains, without being predominant. As a result no significant forest area has been classified as NS in some countries in spite of the occurrence of coniferous species.
NHC stands for closed broadleaved forests, i.e. those which, when not recently cleared by shifting agriculture or heavily exploited, cover with their various storeys and undergrowth, a high proportion of the ground and do not have a continuous dense grass layer allowing grazing and spreading of fires. They are often, but not always, multistoreyed. They may be evergreen, semi-deciduous or deciduous, wet, moist or dry;
NHc/NHO corresponds to mixed broadleaved forest-grassland formations with a continuous dense grass layer in which the tree synusia covers more than 10% (e.g. various forms of “cerrado” and “chaco” in America, tree and wooded savannas and woodlands in Africa, dry dipterocarp forests and Indochinese “forêts claires” in Asia). This division between closed forests and mixed formations is more of ecological than physiognomic type and is not characterised necessarily by a crown cover percentage, since, for instance, trees of some woodlands cover the ground completely like closed forests.
A similar distinction has not been introduced for predominantly coniferous forests (NS) since it has not the same ecological importance and is difficult, if not impossible, to use.
NHCf (or NSf) corresponds to stands of closed broadleaved forest (or coniferous forest) which have not been cleared (for agriculture mainly) in a recent past (i.e. during the last 20 to 30 years). These forests are either managed or unmanaged forests, primary or in an advanced stage of reconstitution after having been cleared at least 60 to 80 years ago (old secondary forests). These forests may have been logged-over once or more times, having kept their characteristics of forest stands, possibly with modified structure and composition through in particular impoverishment in timber species (logging is accounted for in a subdivision of this category - see below).
NHCa (or NSa), or “forest fallow”, stands for all complexes of woody vegetation deriving from the clearing by shifting cultivation of closed broadleaved forests (or coniferous forests) and constituted by a mosaic of various reconstitution facies (“secondary bush”, “young secondary forests”, stands of Musanga, “secondary growth”). Patches of uncleared forest and of agricultural fields are generally included in those areas as it is impossible to account for them separately within the shifting cultivation areas (in particular in the visual interpretation of satellite imagery). When site conditions are unfavourable (e.g. broken terrain) or when the fallow period is reduced to a very short period, clearing by agriculture leads to such a degradation of the site that the reconstitution of the forest is not possible within a foreseeable future; the resulting degraded vegetation is not included in the NHCa (or NSa) category but in shrub formations (n) or outside woody vegetation.
NHCf1 (or NSf1) are “productive” closed broadleaved forests (or coniferous forests"), managed or not: their characteristics, those of the terrain and the present regulations allow (or might allow) for the production of wood for industry (sawlogs and veneerlogs, pulpwood, pitprops and other industrial poles). Their distance to consumption or export centres is not taken into accoutn, i.e. this category may include economically inaccessible forests.
NHCf2 (or NSf2) include “unproductive” closed broadleaved forests (or coniferous forests). They are subdivided in:
NHCf2i (or NSf2i) which are unproductive for physical reasons, i.e.:
those which cannot produce wood for industry because of their characteristics (forests with stunted and crooked trees, or made of monocotyledon species such as palm or rattan stands);
those which are inoperable because of terrain conditions (terrain too rough or permanently inundated);
NHCf2r (or NSf2r) which are unproductive for legal reasons, i.e. in which logging is prohibited by law or other regulations (e.g. national parks, integral reserves, biosphere reserves etc.).
When forests belong to both categories NHCf2i (or NSf2i) and NHCf2r (or NSf2r) at the same time, their areas is accounted for only in the latter one.
Whenever possible, similar divisions are made within the mixed broadleaved forest-grassland formations category, between productive (NHc/NHO1) and unproductive types (NHc/NHO2) and, within the latter category, between those (NHc/NHO2i) which are unproductive for physical reasons (stand and terrain characteristics) and those (NHc/NHO2r) which are unproductive for legal reasons (e.g. included in national parks).
Mixed broadleaved forest - grassland formations in the various reconstitution stages after clearing by agriculture are indicated by the symbol (NHc/NHOa). Areas indicated for this category, when their estimation has been possible, include also agricultural fields and patches of untouched formations (as for NHCa category) because of difficulty in separating them from the rest of the secondary vegetation.
NHCf1m (or NSf1m) are productive closed broadleaved forests (or coniferous forests) intensively managed. The concept of intensive management is used here in a restricted way and implies not only the strict and controlled application of harvesting regulations but also silvicultural treatments and protection against fires and diseases. These forests constitute the part of the permanent productive forest estate in a given country to which the concept of “annual allowable cut” can be meaningfully applied.
NHCf1u (or NSf1u) stands for the productive closed broadleaved forests (or coniferous forests) other than those intensively managed. They are separated in two groups:
NHCf1uv (or NSf1uv) are the unmanaged productive closed broadleaved forests (or coniferous forests) undisturbed (or “virgin”), i.e. primary forests or old secondary forests where there has been no logging for the last 60 to 80 years;
NHCf1uc (or NSf1uc) are those which have been logged-over once or more times during the last 60 to 80 years (the very large majority of the remaining ones have been exploited in fact in the last 30 years or so).
nH and nS stand for vegetation types the main woody elements of which are shrubs of broadleaved and coniferous species respectively. In most cases no subdivision has been introduced within these categories for lack of precise information. In many mixed broadleaved forest-grassland formations, separation between those in which trees are the predominant woody elements (NHc/NHO) and those in which they are the shrubs (nH) is often approximative.
A summarized definition of the various classes with their corresponding symbols, as used in the presentation of results, is given below (in the order they appear in the table of area statistics):
|NHCf1uv||:||undisturbed productive closed broadleaved forests not (intensively) managed;|
|NHCf1uc||:||logged-over productive closed broadleaved forests not (intensively) managed;|
|NHCf1u||:||productive closed broadleaved forests not (intensively) managed;|
|NHCf1m||:||(intensively) managed productive closed broadleaved forests;|
|NHCf1||:||productive closed broadleaved forests;|
|NHCf2i||:||closed broadleaved forests unproductive for physical reasons (stand and terrain characteristics);|
|NHCf2r||:||closed broadleaved forests unproductive for legal reasons;|
|NHCf2||:||unproductive closed broadleaved forests;|
|NHCf||:||closed broadleaved forests;|
|NHCa||:||forest fallow (of closed broadleaved forests).|
Equivalent categories of coniferous, bamboo and closed forest have similar symbols in which NHC is replaced by NS, NHB and N. respectively.
|NHc/NHO1||:||productive mixed broadleaved forest-grassland tree formations;|
|NHc/NHO2i||:||mixed broadleaved forest-grassland tree formations unproductive for physical reasons (stand and terrain characteristics);|
|NHc/NHO2r||:||mixed broadleaved forest-grassland tree formations unproductive for legal reasons;|
|NHc/NHO2||:||unproductive mixed broadleaved forest-grassland tree formations;|
|NHc/NHO||:||mixed broadleaved forest-grassland tree formations;|
|NHc/NHOa||:||forest fallow (of mixed broadleaved forest-grassland tree formations);|
|n||:||(essentially) shrub formations (broadleaved or coniferous).|
1 These limits must be interpreted with flexibility, particularly the minimum tree height (and maximum shrub height) which may vary between 5 and 8 metres approximately.
2.2 Classification of plantations (P)
The term “plantation” corresponds to 1:
forest stands established artifically by afforestation on land which previously did not carry forest;
forest stands established artifically by reforestation on land which carried out forest within the previous 50 years or within living memory and involving the replacement of the previous crop by a new and essentially different crop.
Plantations in the sense used in this study do not include stands established by artificial regeneration and essentially similar to those they are replacing. These artificially regenerated forests are part of productive closed broadleaved (or coniferous) forests (intensively) managed (NHCf1m/NSf1m).
A distinction is made between industrial plantations (P..1) established totally or partly for production of wood for industry (sawlogs and veneer logs, pulpwood, pitprops mainly) and non-industrial plantations (or “other plantations”) (P..2) established mainly for one or several of the following objectives:
production of fuelwood and wood for charcoal (possibly as industrial energy source);
production of small wood for domestic consumption (in particular by rural populations);
non wood products (fruits from forest trees, palm hearts, gum arabic, cinnamon etc.);
Those tree plantations which are usually outside the competence of foresters are not accounted for. This is the case in particular of plantations of rubber trees, palm oil trees, coconut trees, and of the shade tree plantations for agriculture.
A distinction is made between plantations of broadleaved species, or hardwood plantations (PH.1/PH.2), and plantations of coniferous species, or softwood plantations (PS.1/PS.2).
Hardwood plantations are divided between plantations of fast-growing species (PHH1/PHH2) and plantations with other broadleaved species (PHL1/PHL2). Limit between these two groups of species corresponds approximately to a gross mean annual increment of 12–15 m3/ha/year. However, separation is made above all on the basis of the species. For instance Eucalyptus and Gmelina plantations are classified as fast-growing species (PHH1/PHH2), whereas teak plantations are included in the PHL1/PHL2 categories.
The categories of plantations are finally the following:
|●||PHL1:||industrial plantations of hardwood species other than fast-growing ones;|
|PHH1:||industrial plantations of fast-growing hardwood species;|
|PH.1:||industrial hardwood plantations;|
|PS.1:||industrial softwood plantations;|
|●||PHL2:||non-industrial plantations of hardwood species other than fast-growing ones;|
|PHH2:||non-industrial plantations of fast-growing hardwood species;|
|PH.2:||non-industrial hardwood plantations;|
|PS.2:||non-industrial softwood plantations;|
|●||PHL=PHL1 + PHL2:||plantations of hardwood species other than fast-growing ones;|
|PHH=PHH1 + PHH2:||plantations of fast-growing hardwood species;|
|PH =PH.1 + PH.2:||hardwood plantations;|
|PS =PS.1 + PS.2:||softwood plantations;|
|P =P..1 + P..2:||all plantations.|
1 The following categories were defined on the occasion of the World Symposium on Man-made Forests and their Industrial Importance (Canberra - Australia, 14–24 April 1976).
2.3 Concepts of volume
Three volume concepts (either volume per ha or total for a given forest category) are used throughout this study for closed broadleaved forests and coniferous forests (NHC-NS) and for productive mixed broadleaved forest-grassland tree formations (NHc/NHO1), which are:
|●||VOB:||gross volume over bark of free bole (from stump or buttresses to crown point or first main branch) of all living trees more than 10 cm diameter at breast height (or above buttresses if they are higher);|
|●||VAC:||(for forests not intensively managed): volume actually commercialized, that is volume under bark of logs actually extracted from the forest;|
|●||AAC:||(for intensively managed forests): gross annual allowable cut, in general equated with current annual yield.|
Lack of recent data in Burma, Orissa state and the northeastern region of India, Viet Nam and those parts of Kampuchea and Lao not covered by the vegetation map of the Committee for Coordination of Investigations of the Lower Mekong Basin prompted to decide for the interpretation of Landsat imagery for these countries and areas. The main purpose of the work of satellite imagery interpretation was the checking and possible correction of estimates derived from a previous attempt to update maps and other available documents. Because of the global nature of this study, of the extent of the categories used and in the case of Indochina, of the impossibility of collecting detailed ground truth data, the work was limited to the visual interpretation of images, more precisely of the 1/1 000 000 scale positive transparencies of bands 5 to 7 and the standard colour composition from bands 4,5 and 7. The interpretation work benefited from the experience acquired by the FAO Forestry Department within the framework of the FAO/UNEP Pilot Project on Tropical Forest Cover Monitoring. The remote sensing consultant in charge of the interpretation work for the Indochina countries (J. Guellec) had participated in this pilot project. The interpretation work of the Orissa and northeastern states of India was carried cut by J.P. Aggarwal, remote sensing specialist of the Indian Preinvestment Survey of Forest Resources. This expert served as consultant to the Burmese Forest Department to train national foresters in the application of the same methodology to the whole of Burma.
The selected scenes are all images from Landsat 1 and 2, from 1972 to 1978 with clouds cover less than 10% above the territory of the countries concerned. The selection was made with the help of the Remote Sensing Unit of FAO using the microfiches of the print-out lists per country, and the microfilms of band 5 for checking the quality of each scene and the location and distribution of the clouds.
For the Indian state of Orissa and for Burma actual “ground truth” data were collected in the field to support the visual interpretation of Landsat imagery, in addition to information contained in existing vegetation and land-use studies (such as forest inventory maps and reports of the Indian Preinvestment Survey of Forest Resources and the Burmese Forest Department, the “Forest Atlas of India” and the 1/1 000 000 vegetation map of India by the Scientific and Technical Section of the French Institute of Pondichery). In the case of the Indochina countries “ground truth” data consisted mainly in the use of available vegetation and land-use studies and forest inventory reports and maps. A more detailed manual interpretation of Landsat imagery was to be carried out later on in Viet Nam for forestry purpose within the framework of the UNDP/FAO/Viet Nam “Assistance to the Forest Inventory and Planning-Institute of Viet Nam” project.
This global project does not aim at drawing forest maps but mainly at assessing the present situation and evolution of tropical forest resources qualitatively and quantitatively. Moreover the delineation of the various vegetation types from satellite images is not obligatory since area estimates can be obtained on a statistical basis through the identification of vegetation types at each dot of a grid. The delineation of the various types on the imagery and the transfer of limits on to a base map has therefore not been carried out systematically. This more complete latter approach was followed in the case of India and Burma and the areas of the various classes determined by dot counting on the 1/1 000 000 scale scale maps obtained. For the Indochina countries the statistical method consisting in the interpretation of the vegetation at each dot of a grid on the imagery was preferred. A systematic dot grid on transparent stable material, with a 5mm by 5mm spacing in the directions parallel to the sides of the images, was applied on the transparencies observed on a mirror stereoscope. Band 5 or 7 was usually visualised simultaneously with the coulour composition on the stereoscope. The dot grid was limited to the effective part of the images, taking into account an average lateral overlap of 20% in the tropical regions 1 and a forward lap along the orbit of 10%. Before the interpretation itself, some important features were indicated on one transparency of each some, such as international boundaries, rivers, important roads in order to facilitate orientation.
The results of the two approaches were compared on an experimental basis. Differences for each class, such as closed forests, open forests, degraded forests, were not systematic and did not exceed 4% when these types were in the form of large areas. Differences were high and systematic for classes represented by scattered patches of small dimensions. In this latter case the smallest patches are not delineated and the total area of the corresponding class is underestimated, while the estimation by interpretation of dots is not biased from this aspect. Another advantage of the statistical method is to allow for reduction of the personal bias of the interpreter in the delineation of the class, more particularly in the transition zones where the drawing of the limits is often somewhat subjective.
An account of the classification used in India and Burma is given in the corresponding country briefs, in the second part of this report (see in particular annex 1 of the India country brief). For Viet Nam and selected parts of Kampuchea and Lao the key was slightly refined in order to match more closely the one used by the Committee for Coordination of Investigations of the Lower Mekong Basin. In both cases compatibility was secured between these classifications and the standard one used in this study (see paragraph 2.1.3).
In total the following numbers of scenes, either complete or partial, were interpreted: 80 for India (whole Orissa state and northeastern region) and Burma (whole of the country) except a small area in the Chin hills near the Indian border) and 36 for the Indochina countries (the list of which is given in the annex 1 of the country briefs of Kampuchea, Lao and Viet Nam).
Use has also been made in this study of the results of remote sensing interpretation carried out during the last years for vegetation mapping at national level in Indonesia, Philippines and Thailand.
1 The average overlap is approximately 14% on the equator and 24% on the tropics (23°27').
4.1 Country briefs
The first part of this report summarizes the results obtained for the whole of the 16 countries concerned of tropical Asia, while the second part contains the country briefs. The 16 countries are:
all the Asian countries (15) situated south of China from Pakistan to the west to the Indonesian part of the island of New Guinea to the east (Irian Jaya) with the exception of the Maldives and Singapore. More than half of the land area of these countries is located with the tropical belt, except Bhutan, Nepal and Pakistan which are entirely above the tropic of Cancer. They have been included because they are part of the same subcontinent and are presenting similar features as the neighbouring regions of India. Moreover tropical and subtropical climatic influences are perceptible quite north of the tropic of Cancer;
Papua New Guinea: although it is generally considered as an Oceanian country it has been included in the study because of its relatively large area entirely within the tropical belt and the fact that it shares with Indonesia the island of New Guinea. The study does not cover Australia, although it has a significatn part of its land area within the tropical belt nor its tropical territories, nor any other Oceanian country or territory.
The 16 studied countries of tropical Asia
CONTINENTAL SOUTHEAST ASIA
INSULAR SOUTHEAST ASIA
CENTRALLY PLANNED TROPICAL ASIA
The outline is the same for all country briefs. The present situation of forest resources and their trends are described in two separate sections, each of them with a part describing natural woody vegetation and another one on plantations.
Descriptions of the composition and physiognomy of the various types of natural woody vegetation (paragraph 1.1.1) is followed by an estimation of areas of natural woody vegetation at the end of 1980 and by information on ownership, status management and utilization of the forests (paragraph 1.1.2). The interpretation of available forest inventory results allows for an estimation of growing stock at national level at the end of 1980 (paragraph 1.1.3).
The comments on forest plantations contain an introduction (paragraph 1.2.1) dealing in particular with historical aspects followed by the estimation of forest plantation areas at the end of 1980, separately for industrial plantations and other plantations, each group by species categories and age classes (paragraph 1.2.2). Quantitative data on plantation characteristics, particularly on mean annual increments, are given in paragraph 1.2.3.
In section 2.1 on present trends of natural woody vegetation, an important distinction has been introduced between, on one hand, deforestation in the strict definition of the term (paragraph 2.1.2), i.e. alienation of forest areas to permanent or shifting agriculture or to other uses, and, on the other hand, degradation of woody vegetation (in particular of mixed forest-grassland formations) which results from other factors such as fire, overgrazing, overploitation for fuelwood and charcoal, etc (paragraph 2.1.2). In most cases degradation does not show up so much as a decrease in the area of woody vegetation but rather as a gradual reduction of biomass, changes in specific composition and soil degradation. Unfortunately these changes are very seldom quantified, and never at nation or subnational levels. Taking into account trends in forest utilization (paragraph 2.1.3), area and growing stock estimates are then projected at the end of 1985 (paragraph 2.1.4).
In section 2.2, forest plantation programmes are mentioned as well as their probable rates of implementation in the period 1981–85. This allows for the projection of planted areas by species category up to the end of 1985.
A bibliography at the end of each country brief lists the main documents which have been used for assessing forest resources and their trends. These references are presented in chronological order, since the date of publication is particularly relevant to such a study.
In addition to some tables related to less important issues a number of basic tables have been set out to illustrate the text, as shown below:
“Areas of natural woody vegetation estimated at and of 1980” (paragraph 1.1.2)
This table provides areas (to the nearest thousand ha) of natural woody vegetation classes according to the classification presented in section 2.1 above. Area estimates at the end of 1980 are derived from corresponding areas at previous reference dates, which may be that of an inventory, a reconnaissance a map at national level, and which are corrected to account for deforestation during the period between this reference date and 1980. Explanatory comments follow the table.
“Growing stock estimated at end 1980” (paragraph 1.1.3)
On the basis of area estimates given in the above table and of mean gross volumes per ha (VOB) and of mean “actually commercialised volumes” (VAC) (to nearest m3), derived from forest inventory results and other data, it is possible to obtain estimates of total volumes for closed broadleaved forests, coniferous forests and productive open forests (NHc/NHO1). An estimate of mean and total volumes of forest fallow areas (NHCa, NBa NHc/NHOa) has not been attempted because of the wide diversity of corresponding classes and lack of volume data. For the same reasons the volumes of unproductive open forests and of shrub formations (n) have not been estimated.
Standing commercial volumes (VAC) are estimated only for virgin productive closed forests (NHCf1uv/NSf1uv) for which the volume extracted per ha is generally well known. Logged-over productive closed forests (NHCf1uc/NSf1uc) also contain exploitable volumes and some forests are indeed “creamed” twice or even more. However, it remains difficult, if not impossible, to assess the average commercial volume remaining in logged-over forests and no corresponding figures are given except in a few cases.
When no information is available on gross volumes (VOB) of logged-over productive closed forests (NHCf1uc/NSf1uc) it has been taken to equal the gross volume of the original virgin forest minus twice the volume of the extracted logs (2 x VAC) i.e. minus the gross volume of felled trees. This simplification assumes compensation between harvesting damage in the forests (negative factor) and the forest growth after logging (positive factor).
“Areas of established plantations estimated at end 1980” (paragraph 1.2.2)
Areas successfully planted until the end of 1980 are given in thousand ha (in general to the nearest 100 ha) by species groups and age classes, respectively for industrial plantations, non-industrial plantations, and all plantations. These estimates are net areas, which take into account rates of programme implementation, the beating up of unsuccessful plantations or the reforestation of logged-over plantations and the failure of some others. No detailed inventory of plantations at national level exists in any tropical Asian country, and this makes the estimation of the present situation difficult. In some cases, estimates of gross areas found in the documentation have been mentioned for the sake of comparison.
Some plantations have already been logged and replanted, or have coppiced, in which case, distribution by age class has often been given not only from the time of the first planting but also from the time of the new generation.
“Average annual deforestation” (paragraph 2.1.1)
This table gives areas of closed forests which have been cleared per year during the last five years (1976–80) and the corresponding projections for the next five years. As already mentioned, the concept of deforestation as used in this study applies the clearing of forest land for uses other than forestry (mainly agriculture), and its possible substitution, after a few years, by a secondary tree growth.
A logged-over forest which is not occupied by agriculture changes in forest category (from NHCf1uv/NSf1uv to NHCf1uc/NSf1uc) but is not deforested in the meaning used in this study, even if the extracted volume is relatively high. This type of transfer from virgin forests to logged-over forests is not reflected in this table. To determine the area of primary forest converted every year by clearfelling and by logging, one must add the area of virgin forest newly logged each year to the deforestation figure mentioned in this table.
In paragraph 2.1.1 indications are also given about the transfer of closed forests (NHCf/NSf) to corresponding forest fallow (NHCa/NSa) resulting from shifting cultivation in terrain of easy topography where soil reconstitution after cropping is possible.
Destruction of open tree formations (NHc/NHO) and that of shrub formations (n) are also mentioned in this paragraph, as well as transfers within the NHc/NHO category, and those to n category.
“Areas of natural woody vegetation estimated at end 1985” - “Growing stock estimated at end 1985” (paragraph 2.1.4)
These tables are similar to those of paragraphs 1.1.2 and 1.1.3. They provide estimates of areas and corresponding volumes as they have been projected on the basis of deforestation estimates for the next five years and of other assessments related to conservation and utilization of forests in the period 1981–85.
“Areas of established plantations estimated at end 1985” (section 2.2)
These tables are similar to those of paragraph 1.2.2 and take into account the projected areas of plantations established during 1981–85 on the basis of existing or planned programmes and of financial and other contraints faced by each country.
4.2 Results at regional level
The presentation of results at regional level in the next chapter uses the same outline as that of the country briefs. In the tables each line corresponds to a country and the countries are grouped in following subregions:
|●||South Asia (6)||:||Bangladesh, Bhutan, India, Nepal, Pakistan, Sri Lanka;|
|●||Continental southeast Asia (2)||:||Burma, Thailand;|
|●||Insular southeast Asia (4)||:||Burnei, Indonesia, Malaysia (Peninsular Malaysia, Sabah and Sarawak), Indonesia;|
|●||Centrally planned tropical Asia (3)||:||Kampuchea, Lao, Viet Nam;|
|●||(Oceania)||:||Papua New Guinea.|
The 16 countries grouped as tropical Asia in this study are the following (in alphabetical order): Bangladesh, Bhutan, Brunei, Burma, India, Indonesia, Kampuchea, Lao, Malaysia, Nepal, Papua New Guinea, Pakistan, Philippines, Sri Lanka, Thailand and Vietnam. For the presentation of results these countries have been arranged into five subregions as indicated in paragraph 4.2 of Chapter II.
The total surface area of these 16 countries is close to 9.45 million km2. They extend between latitudes 37°N and 12°S and longitudes 61°E and 156°E. A greater part of the geographic area (48 percent) is accounted for by the south Asian countries. The five largest countries studied are: India, Indonesia, Pakistan, Burma and Thailand with 3.29, 1.92, 0.80, 0.68 and 0.51 million km2 respectively.
a) South Asia has a large variety of land forms ranging from high mountains to plateaus of various kinds, alluvial plains and sandy deserts. The most outstanding feature of the region, however, is the Himalayas which extend over a distance of some 3 750 km between the gorges of the Indus and Brahmaputra rivers. The main range, with Everest (8 848 m), Kanchenjunga (8 597 m), Dhaulagiri (8 137 m), and many other giant peaks, forms the core of the system, to which the trans-Himalayas on the north, the outer Himalayas on the south, and lesser subsidiary ranges give width and body. The Himalayas have affected profoundly the climate, geology and the formation of vegetation types in India, Nepal, Bhutan and Pakistan. The North Indian plains are a great alluvial tract formed by the basins of the three main rivers Indus, Ganga and Brahmaputra which all originate in the Himalayas. The peninsular plateau bounded by the Eastern and Western Ghats where hill ranges rise generally from 900 to 1 200 m (in places over 2 500 m) are a marked feature of the Indian subcontinent below the Vindhya mountains. The narrow coastal strips between Western Ghats and the Arabian Sea and between Eastern Ghats and the Bay of Bengal are a distinct physiographical feature of India. In Pakistan in addition to the northern parts under the distinct influence of Himalayas, the Indus plain in the western part and the coastal fringe bordering the Arabian Sea are the other noteworthy geographical features. The delta formed by the confluence of Ganga and Brahmaputra and the series of parallel ridges on the eastern border (Chittagong Hill Tracts) are the conspicuous features of Bangladesh. In Sri Lanka there are highlands in the central and southwestern parts (rising to elevations higher than 2 000 m), lowland plains in the northern half of the country and narrow coastal strips all round the island. The Mahaweli Ganga river is a prominent feature of the landscape.
Geologically the Indian land mass is part of Gondwanaland. It has a basement of archaean rocks, probably formed by solidification of the earth's original crust (after D.W. Wadia in “Geology of India”). The more important rock formations are: archean gneiss, granite, quartzite, slate and schist (Himalayan ranges); sandstone, clay and conglomerate (Siwalik system); sandstone, shale, slate limestone (the Cuddapah and Vindhyan systems); basalt (Deccan trap). A unique feature of this subregion is the Thar desert (mainly in India but extending into Pakistan) which is a vast expanse of sand deposits with a few outcrops of old basement rocks.
In the north and northwestern regions of Burma, there are hill ranges bordering China, Lao and Thailand. A major river draining the central plains of the country is Irrawaddy In Thailand the northern region consists of a series of parallel and longitudinal fold mountains extending through peninsular Thailand into Malaysia. The average height of the peaks is 1 600 m with some above 2 000 m. Chao Phraya river drains the major part of the country; the Mekong river forms the eastern boundary. The geography, vegetation, economy and culture of Kampuchea are influenced by the vast Mekong delta, while Lao is predominantly mountainous. The main features of the relief of Vietnam are: largely mountainous terrain in the northern region bordering China and the central region between 8°N and 16°N parallels; the plains around Hanoi extending southward in a narrow coastal belt and the Mekong delta in the extreme south.
Peninsular Malaysia has a maximum width of only 322 km and a length of 740 km and is featured by parallel mountain ranges with peaks rising sometimes to more than 2 000 m. There are extensive coastal plains. The Malaysian state of Sabah is situated at the northern tip of the island of Borneo. Large areas of low and flat land in the west and the Walker Range of mountains (Mt. Kinabalu: 4 100 m) running parallel to the coast are the chief features. Sarawak (Malaysia) is also located in Borneo island and is characterised topographycally by a seaward fringe of peat swamps and a mountain range at the border with the Indonesian part of the island (Kalimantan). Indonesia is an archipelago with some 13 600 islands of which only 6 000 are inhabited. General topography of the three large islands (Sumatra, Kalimantan and Irian Jaya) is characterised by extensive coastal plains and inland mountainous areas up to or more than 3 000 m elevation. The important mountain ranges are in western Sumatra, central Kalimantan, central Irian Jaya and in Sulawesi. Java has a series of fifteen volcanoes with fertile plains between them and a broad northern coastal plain. The Philippines consist of 10 large islands and about 7 000 small ones; nearly all the islands have rugged interior upland rising usually to between 1 250 and 2 500 m. The highest mountain, Mt. Apo in Mindanao, reaches 2 954 m while Mt. Pulong in Luzon is 2 929 m high. Lowlands are scarce; the most important lowland areas are in Luzon, in Mindanao (Agusan and Cotabato plains) and in western Negros and eastern Panay.
Geologically two major morphostructural regions can be distinguished in southeast Asia (after FAO/Unesco in “Soil Map of the World”; Vol IX). The Sundra Shelf area includes the Malay Peninsula, Thailand, Indochina and Borneo island. The Malay Peninsula consists of granite core and locally metamorphosed rocks of limestone, shale and sandstone. In western Thailand the rock formations are carboniferous (Kanchanaburi series), while in the east sandstone, conglomerate, limestone and locally metamorphosed quartz-phyllite and slate (Korat series) are found. The Korat series predominates throughout Indochina also. The Mekong and Chao Phraya river basins consist of recent and older alluvial deposits of silt and clay which are sometimes interbedded with sandy layers. In Borneo the important rock formations are: quartzite, shale, sandstone, limestone, crystalline schist, etc. The circum-Sundra orogenic system includes the Philippines in the northeast and merges south-westward into the great Sundra mountain system: Moluccas (Maluku), Celebes (Sulawesi), lesser Sunda Islands (Nusa Tenggara) Java, Madura and Sumatra of Indonesia. The Philippines are characterized by high tectonic instability and volcanic activity. The basement consists chiefly of pre-jurassic igneous rocks which outcrop in extensive areas of Mindanao, Palawan, Mindoro and Leyte. Granites are widely represented. In Indonesia volcanic deposists are extensive in Java and Madura; metamorphic crystalline schists and tertiary rock formations abound in Sumatra.
b) Soils in tropical Asia are enormously varied. 19 soils regions are recognised in the countries of tropical Asia by the FAO/Unesco study “Soil Map of the World” Volumes VII and IX). Here it is proposed to highlight only a few broad features of the soils in the region.
Starting with the northwestern part of south Asia (Indus plain of Pakistan, parts of India) it is found that these areas are predominantly arid and semi-arid and the soils are mainly calcic and haplic xerosols (brown to dark brown; silty clay loam; moderately calcareous; pH>8.0). In the Thar and Thal desert area the dominant soils are cambic arenosols (pale brown loamy sand). Very deep black soils (vertisols) somewhat poorly drained and olayey are found in extensive areas in western India. In the Indo-Gangetic plains (northern India) and the Ganges-Brahmaputra delta (Bangladesh and adjoining parts of India) fluvisols or alluvial soils predominate. In the soil region which extends over the eastern and southern parts of peninsular India and all of Sri Lanka the soils are mainly reddish brown and loamy (luvisols/nitosols). Cambisols (very dark greyish brown; sandy loam; pH>6.0) predominate in the mountainous humid tropical areas of Burma, Bangladesh and India.
In southeast Asia acrisols are the most widespread and cover nearly half area. These soils form an acid to moderately basic parent material. They are fine to medium textured, dark greyish brown, clay to sandy loam with a pH range of 5.0 to 6.0. Acrisols are very poor in nutrients and highly susceptible to erosion. They occur over vast tracts of the main mountain systems of Vietnam, Lao, Kampuchea, Thailand, Peninsular Malaysia, and of the islands of Sumatra, Borneo, Sulawesi and New Guinea. The plains of the major rivers Chao Phraya and Mekong are predominantly alluvial (fluvisols). Acrisols are found in association with nitosols (fine textured, deep, well drained, sandy clay loam, ph: 6.5) in parts of Java and the Philippines. Nitosols, per se, are restricted to local basalt plateaus; two main occurrences are in the central highlands of Thailand and the plateau des Bolovens in Lao. Podzols (dark reddish brown with decomposed humus) occur in southern Kalimantan (Borneo) and eastern coast of Sumatra. Histosols (permanently wet, with the water table close to soil surface) of southeast Asia are estimated to cover some 23 million ha and are found in the vast coastal peat-bogs of the islands of Sumatra, Borneo, New Guinea and, to a lesser extent, the Malay Peninsula.
c) Pronounced climatic contrasts are characteristic of the south Asia subregion. The mercury may rise above 50°C at Jacobabad (Pakistan) and falls below -10°C in the snowy regions of Kashmir and Nepal. A climb of only a few kilometers changes the temperatures from hot (40°C) at the foothills (Terai) of Himalayas to near arctic cold above the snow on Himalayan tops. In the Indian subcontinent three seasons are generally distinguished: winter (November–February), summer (March–June) and the rains (July–October). The North Indian plains are characterised by extreme hot and oppressive weather in summers and cool to cold winters. The contrasts in rainfall are even greater and have a profound effect on vegetation: the extremes range from an annual mean of 75 mm in upper Sind (Pakistan) and Rajasthan to 12 000 mm at Chirrapunji (Indian state of Assam). The bulk of the rainfall in the subcontinent is brought by the southwest monsoon during the four months from July to October. One great current of the monsoon bursts against the Western Ghats and flows over the Deccan, another sweeps up the Bay of Bengal, and, combined, they wash the sub-continent. In winter (November–January) the northeast monsoon brings rain to some parts of India. The high rainfall areas lie in the northeast and on the west coasts of India and Sri Lanka. A narrow strip along the Himalayas also receives considerable rainfall. The general decrease in rainfall is from east to west and north to south, so that the northwestern part of India and most of Pakistan receive very little rainfall. In India and Pakistan the variability of the monsoon summer rain is considerable, ranging from about 20 percent in areas receiving more than 1 000 mm normal rain to about 50 percent in areas having less than 500 mm rainfall. Such variations result in frequent floods and droughts (after M.S. Randhawa in “Agriculture and Animal Husbandry in India”). During April to June and October to December severe cyclones usually form in the Bay of Bengal and the Arabian Sea and severely affect the coastal areas of Bangladesh and India's east coast. The northeasterly winds bring considerable rain in Sri Lanka as well.
In southeast Asia average temperatures remain practically uniform (around 27°C) throughout the year in most of the region lying south of 17°N parallel. Further north the mean range of temperature increases slightly with latitude in coastal regions, but shows high variation in inland areas. In Thailand the highest temperatures of the year are registered during March–April, when day temperatures rarely fall below 32°C. In Lao, Kampuchea and Vietnam, the climate is tropical in the southern parts, but in the north winters are moderately cool. In Peninsular Malaysia, owing to maritime exposure, the annual mean daily range of temperature does not exceed 9°C. The highest temperature ever recorded in the peninsula is 39.4°C. Indonesia, Sabah and Sarawak, which lie within 10°N and 10°S parallels and are surrounded by warm tropical seas, experience a hot, humid climate in all seasons. The mean annual rainfall varies widely from one country to another. In the continental countries it ranges from 1 000 to 1 800 mm, in Peninsular Malaysia from 2 000 to 3 000 mm, and in several parts of insular southeast Asia from 1 800 to 3 000 mm. The continental countries are influenced by the northeast monsoon from October to February–March and by the southwest monsoon from May to September; almost 80% of the annual rainfall occurs from May to September. Indonesia experiences the west monsoon from November to March and the east monsoon from June to September. With the exception of their eastern parts, the Philippines receive most of their annual rainfall from May to October. Based on rainfall, four zones are distinguishable in southeast Asia:
zone I: areas with more than nine consecutive wet months with more than 200 mm rainfall per month. This zone includes the major part of Kalimantan and east Malaysia, central Sumatra the northwest coast of Sumatra, isolated spots in Java (primarily the southwestern part) and the eastern part of the Philippines;
zone II: areas with five to nine consecutive wet months with more than 200 mm rainfall. This zone covers the southern part of Burma, the southern and eastern parts of Thailand, the entire Lao, eastern Kampuchea, the western part of Vietnam, the major part of Peninsular Malaysia, the major part of Sumatra and the western and central parts of Java, as well as a large part of Luzon, the Visayas, and Mindanao in the Philippines;
zone III: areas with two to five consecutive wet months, and a short wet season with rainfall of about 100 mm per month. Western Thailand, central Kampuchea, the east coast of Vietnam, the northern tip of Sumatra, parts of Java, and a major portion of Sulawesi fall into this zone;
zone IV: areas with less than two consecutive wet months. These areas are located in northeast Thailand, north Burma, east Kalimantan, some parts of Sulawesi and Nusa Tenggara in Indonesia and central Visayas in the Philippines.
d) In 1979, the total population of the 16 countries was approximately 1 230 million, about 28% of the world population. More than 70% of the people lived in south Asia, 12% in continental southeast Asia and the rest in insular southeast Asia and Papua New Guinea. India, Indonesia, Bangladesh and Pakistan are the four largest on the basis of size of their populations with 678, 148, 86 and 74 million respectively. Together they account for 88% of the region's population. The growth rate of population ranged during the period 1975–79 from a low of 1.8% in Sri Lanka to a high of 3.4% in Brunei. Most countries have a growth rate of population between 2.0% and 3.0%. By the year 2000 according to the World Development Report 1980 of the World Bank the population of the region would be 1 823 million, corresponding to an average annual growth rate of about 1.9%. The share of the region in the estimated world population in 2000 of some 6 billion would be about 30%.
Bangladesh is the most densely populated country in the region with over 600 inhabitants per km2. The other densely populated countries of the region with a population density of 60 or more persons per km2 in 1979, in decreasing order, are Sri Lanka (223), India (206), Philippines (157), Vietnam (155), Pakistan (100), Nepal (99), Thailand (90) and Indonesia (78). Within the countries some parts are more densely populated than others. In general population is concentrated in the surrounding areas of fertile plains, river valleys and urban centres. Mountainous regions and some of the richly forested areas are sparsely populated. For example, in Indonesia, the inhabitants per square kilometre in Irian Jaya, Kalimantan and Sumatra, which are endowed with rich forest resources, are 2.10 and 43 respectively when compared with 610 in Java and 410 in Bali. Similarly in Sabah, where forests abound, the population density is only 14 persons per km2; in Sarawak it is 52 as against 86 in Peninsular Malaysia. Such variations are observed in nearly all countries of the region. Over the years the trend is not only towards an overall increase in population density but also a steep rise in agricultural population per hectare of crop land. In 1979 the estimated agricultural population in the region was 791 million or 64% of the total population. The proportion of agriculture population to the total varies widely: 47% in the Philippines to 93% in Nepal. Agriculture is still the dominant sector in the economy of the region and in 1978 contributed between 25% (Malaysia) to 60% (Lao) of the gross domestic product. There is a noticeable decline in the share of agriculture in the total GDP in 1978 compared with 1960 - from 50% to 38% on the average for the region as a whole. The countries of the region where agriculture constitutes more than 40% of the GDP (1978) are, according to the World Bank report quoted above: Nepal (62), Lao (60), Bangladesh (57), Burma (46) and India (40). Although the labour force in agriculture as a percentage of total labour force declined from 77% in 1960 to 72% in 1978, agriculture labour force as such continued to grow at an average annual rate of 1% thus aggravating the problem of unemployment and underemployment in agriculture.
The spatial distribution of population has many consequences: social, economic, political, and environmental. The urban population of the world is estimated to have increased by 207 million in the short period between 1970 and 1975, or at the rate of 41 million per annum. Of this growth, 31% occurred in the more developed countries and 69% in less developed. During the past quarter century and especially since 1960 urban-industrial modernization has taken root within the region. In the 25 years between 1950 and 1975, southeast Asia's urban population has almost tripled from 23 to 72 million persons. In the countries of tropical Asia as a whole the average annual growth of urban population increased from 3.7% in the 60's to 4.0% in the 70's. During this latter period, the fastest average annual growth in urban population was registered by Papua New Guinea (8.5%), followed by Bangladesh (6.6%), Vietnam (5.1%), Lao (4.8%), Bhutan (4.5%) and Nepal (4.3%). In the other countries of the region it ranged between 3.3% and 3.7% (World Bank) Urban population as a proportion of total population is the highest in the Philippines (36%) followed by Malaysia (29%), Pakistan (28%), Sri Lanka (27%), Vietnam (23%), India (22%) and Indonesia (20%). In the other countries it was less than 20%, with Bhutan and Nepal at the bottom of the list with urban population constituting only 4 to 5% of the total population. Urbanization has important consequences in determining the future of tropical forests in the region. As growth of cities, industries and infrastructure lay claims on existing arable land the search for oropland to offset this loss constitutes an additional factor of deforestation. The demand for goods (building timber, panels, paper) and services from forestry sector by urban dwellers may result in substantial shifts in the pattern of utilization of tropical forests. Above all, industrial and urban communities which range in size up to several million people exercise political, economic and cultural domination over the rest of the population and thereby influence the trends in resource conservation and utilization.
A worldwide concern about environment and the need to stem the tide of deforestation and degradation has resulted in a renewed focus on the problem of shifting cultivation in tropical forests. Because of its antiquity shifting cultivation has become an integral constituent of the fabric of tribal life. The calendar of operations govern not only the farm operations but also the social life, festivities and religious observations of the tribals. There are some who, despite the destructive nature of shifting cultivation, regard it as an organic response of the people to certain conditions of environment rather than a compulsive adherence to outmoded technology (S.K. Seth in “Agro-Forestry in India”). However, shifting cultivation is to be considered as chiefly responsible for the clearing of tropical forests and there is need for quantifying the population involved and the area affected. This is dealt in some detail under section 2.1.1.
In recent years a new dimension has been added to the problem of pressure on forest land. The excess population in lowland village communities are encroaching into forest land for practising agriculture. Settled hill cultivators, and even land speculators are actively contributing to deforestation in some countries. None of these people have any affinity to the traditional shifting cultivators; their onslaught on forest zones customarily under slash-and-burn have, indeed, aggravated the problem by pushing the traditional shifting cultivators further back into the forests. The spread of organized settlements and colonization schemes, generally government sponsored, and the transfer of land use from forestry to plantation crops like oil palm, rubber, coffee, tea, coconut, etc. has contributed in recent years to depletion of forest cover.
1.1 Natural woody vegetation
The forest flora of the region is rich and varied both in composition and in value. The distribution of forest types, as elsewhere, depends on climatic, edaphic and biotic factors acting in combination. Marked climatic contrasts, pronounced differences in temperatures, rainfalls and soils have given rise to an exceptionally rich variety of forest types.
The forest formations occurring in the region can be broadly viewed as the moist forest types and the dry formations. Among the moist formations are the tropical rain forest and its edaphic variations. Research on tropical rain forest has been mainly on a national or a subregional basis and different systems of nomenclature have been developed. For example, Champion and Seth 1 defined and described the forest types of present day India, Pakistan, Bangladesh and Burma in which the rain forest formations have been described under the nomenclature: tropical wet evergreen forests, tropical semievergreen forests, etc. Whitmore 2 drawing upon the broad structure of Champion, evolved a classification which comprehensively covers the forests of southeast Asia. Several studies also exist on the floristics of non-dipterocarp forests east of the Wallace line which separates the Moluccas, Lesser Sunda Islands, West Irian, Papua New Guinea, etc. from the rest of insular southeast Asia. Thus there is no simple system of classification or a general overall synthesis which encompasses the wide range of floristic diversity in tropical Asia. For the purposes of this study it is considered most useful to adopt one of the existing systems as a broad framework and introduce notes on variations wherever necessary.
1 Champion, H.G. and Seth, S.K. “A Revised Survey of the Forest Types of India”, Dehra Dun (1968), and the earlier version by H.G. Champion of 1936.
1 Whitmore, T.C. “Tropical Rain Forests of the Far East”- Oxford (1975).
1.1.1 Description of the vegetation types
Champion and Seth have divided the forests of India into six major types: moist tropical forests, dry tropical forests, montane subtropical forests, montane wet temperate forests, sub-alpine forests and alpine scrub. Within these types, 16 groups have been identified:
tropical wet evergreen forests;
tropical semi-evergreen forests;
tropical moist deciduous forests;
littoral and swamp forests;
tropical dry deciduous forests;
tropical thorn forests;
tropical dry evergreen forests;
subtropical broadleaved hill forests;
subtropical pine forests;
subtropical dry evergreen forests;
montane wet temperate forests;
himalayan moist temperate forests;
himalayan dry temperate forests;
moist alpine scrub;
dry alpine scrub.
The ensuing description of the vegetation types of tropical Asia follows broadly the above classification of Champion and Seth but confines itself to an overview of only those groups which are of general relevance to the region as a whole. The groups are presented according to the main vegetation categories used in this study.
Closed broadleaved forests (NHC)
a) Tropical wet evergreen forests
These forests are found in warm tropical regions of heavy rainfall and high humidity Temperature and especially rainfall are the most important climatic determinants of the distribution of these forests. In the zones where they occur, average temperatures are above 20°C and annual rainfall is rarely below 1 500 mm and is frequently above 2 500 mm. The dry season does not extend beyond 2–4 months with less than 50 mm rainfall each.
-In south Asia they occur in Chittagong Hill Tracts of Bangladesh. In Bhutan they have a restricted distribution. In India they are found mainly in Andaman Islands, the Himalayan foothills in Assam and a narrow belt along the Western Ghats. In Sri Lanka both montane and lowland evergreen forests occur in the southwestern and central parts. They are closed, multisoreyed forests, with trees of diameter up to 1.5 m and heights varying from 30 to 60 m. The canopy formed by the dominant trees is often overtopped by a few scattered giant individuals. These forests are largely evergreen with a varying proportion of deciduous species and a dense middle storey. Buttressed stems are frequent along with epiphytes, climber, lianas, etc.
The forests are heterogeneous in character. While the number of species is extremely high, most individual species contribute only a minute percentage of the total number of trees. Certain genera tend to predominate. The most widely distributed genera in the lowland wet evergreen forests of south Asia are: Dipterocarpus, Shorea, Palaquium, Hopea, Calophyllum, Mesua, Artocarpus, Sygygium, Vatica, Vitex.
-In continental southeast Asia this formation occurs in southern Thailand just north of the frontier with Malaysia. In Kampuchea and southern Vietnam they occur at low altitudes along the coast where high annual rainfall balances the effect of the short dry season and encourages the development of a dense humid forest of a quasi-equatorial type.
-In insular southeast Asia, Malaysia and the adjacent parts of Indonesia taken together are probably the largest truly everwet area in the world (after P.W. Richards in “Pasoh in perspective”). Together with the Philippines they harbour some of the most dense, high and commercially valuable forests of the region. In its primeval state the truly lowland wet evergreen forests of this subregion exhibits four storeys: the emergent trees (60 m), the dominant and codominant trees in the second storey (45 m), an intermediate layer of trees with canopies between 23 m and to 30 m and the suppressed vegetation. Generally most of the species are soft wood. Besides Dipterocarpaceae, various species of Apocynaceae, Burseraceae, Bignoniaceae, Rhamnaceae,, Leguminosae, Meliaceae, Anacardiaceae, Rutaceae, Sapotaceae, etc. are represented. Nearly 50 percent of the emergent, dominant and codominant stems which constitute the upper storey of these forests are of the Dipterocarpaceae family.
Within the tropical lowland evergreen forests of this subregion there is a great floristic variation between a western block (centred on Sunda shelf around Peninsular Malaysia, Sabah, Sarawak, Kalimantan and Palawan island of Philippines) and the eastern block (centred on the Sulu shelf around Maluku (Moluccas), Irian Jaya and further east). The western block has family dominance of the Dipterocarpaceae in the emergent stratum, and these forests are of greater height than any other broadleaved tropical rain forests in the world (after Whitmore, op. cit.). The main genera of Dipterocarpaceae found here are: Anisoptera, Dipterocarpus, Dryobalanops, Hopea, Shorea and Parashorea. The common non-Dipterocarpaceae genera in the upper storey are: Dyera, Gluta, Intsia, Koompassia, Melanorrhoea, Palaquium, Sindora, Tarrietia, etc. Peninsular Malaysia has 9 genera and 160 species of dipterooarps; in Sabah, Sarawak and Kalimantan 10 genera and 270 species occur. In the Philippines 10 to 11 genera make up to bulk of commercial volume in the forests. The “lauan” or “Philippines mahogany” group, constituted by six species of Shorea and one each of Parashorea and Pentacme, is the most important one. Out of a total of 12 genera and about 470 species of Dipterocarpaceae in Asia, 10 genera and about 350 species are found on the Sunda shelf. In the eastern block (including Papua New Guinea) Dipterocarpaceae are only of local, limited occurrence. The forests of Irian Jaya are typical of non-dipterocarp rain forests in this subregion. Only a few of these species have a world demand and are often traded under the blanket name of “matoa”. The group comprises the genera: Pometia, Intsia, Dracontomelum, Palaquium, Canarium, Octomeles, Vatica, Burckella, Ganua, Madhuca and Mastixiodendron.
b) Tropical montane or hill evergreen forests (group 1/C3 of Champion and Seth)
Under similar conditions as those of lowland evergreen forests but on mountains and high altitudes can be found the montane wet evergreen and semi-evergreen forests. In these forests the number of species is usually less than in lowland rain forests, the canopy is less dense, plank buttresses are scarce, lianas are fewer and smaller. These forests consist typically of oaks, chestnuts, and several species of Magnoliaceae, Lauraceae, Tiliaceae, Rubiaceae, Theaceae, etc., families seldom met within lowland forests. They are represented in India and Bhutan in south Asia. In southeast Asia, the hill dipterocarp forests of Peninsular Malaysia, Sabah and Sarawak consist of many of the species of the lowland dipterocarp forests. With increasing elevation these forests change over into oak-chestnut forests and still higher, over 2 000 m, are replaced by mossy forests rich in conifers and Ericaceae. The subalpine rain forests occur above 3 500 m and have stunted trees of Araucaria, Dacrydium, Podocarpus, Libocedrus, etc. In Papua New Guinea much mountain forest has been destroyed by shifting cultivation. The major genus represented in these forests is Araucaria which is probably restricted to slightly dry lower montane seasonal climates.
c) Tropical semi-evergreen forests (group 2 of Champion and Seth)
With longer dry periods, the evergreen forests are replaced by semi-evergreen and mixed deciduous forests. The semi-evergreen types are found in those regions where the dry periods last no longer than 3 months. These forests consist of both evergreen and deciduous species, the former predominating. They are fairly dense high forests, lower in height than the true evergreen forests and with a lesser number of species. Dipterocarps tend to predominate. Large expanses of this type of forest are found in India, parts of Sri Lanka, Burma, Thailand and insular southeast Asia countries. A great part of the tropical evergreen forests of Thailand are classified as “dry evergreen” but differ in ecology and composition from groups 7 to 10 mentioned later. They are more close to tropical semi-evergreen forests with a predominance of dipterocarps.
d) Tropical moist deciduous forests (group 3 of Champion and Seth)
Tropical moist deciduous forests occur mainly in India, Nepal and Bangladesh in zones where the mean temperatures of the year vary from 20 to 30°C and rainfall between 1 300 and 2 000 mm, and with a dry season of 4–5 months. The type extends from sea level (Andaman Islands) to up to 1 000 m altitude (Nepal). The “monsoon” forests of southeast Asia can also be grouped under this forest type. They are generally closed forests, 30–35 m or more in height and are characterized by the fact that during the dry period all or most of the trees of the upper canopy are entirely leafless. Although the canopy is less dense and the number of species smaller than in the tropical evergreen and semi-evergreen forests, the proportion of commercially valuable species is much higher. Plank buttresses are rare. Woody lianas and other climbers may be present. Epiphytes are confined to water areas. In south Asia the moist teak forests are by far the most valuable from among the forests of this type. Moist teak forests as a rule are a mixture of species, although relatively pure associations in the upper canopy are fairly frequent. Bamboo undergrowth is characteristic. The associates of teak in the top canopy are the genera: Terminalia, Pterocarpus, Lagerstroemia, Albizia spp., Adina, Xylia, Schleichera, Careya constitute the second storey. Bambusa arundinacea in the valleys and wetter areas and Dendrocalamus strictus at the dry end are the common bamboos. In tropical moist sal (Shorea robusta) forests, this species constitutes as much as 60 to 90 percent of the top canopy which is 25–40 m high. An important feature of sal is its semi-evergreen habit with a deciduous period of 5–15 days at the beginning of the hot period. The associate species of this type are similar to that of moist teak forests. In Nepal on higher reaches Pinus roxburghii is a common associate.
Moist deciduous forests where neither teak nor sal dominates occur in India (Andaman Islands, parts of Western Ghats and northeastern region). Typical species in south Asia are: Pterocarpus dalbergioides, Terminalia bialata, T. mannii, T. procera, Canarium euphyllum, Salmalia insignis, Chukrasia tabularis, Albizia lebbek, etc. in the top canopy. In the lower storey species such as Lannea coromandelica, Dillenia pentagyna, Diospyros marmorata are common.
The monsoon forests of Burma, Thailand, Indochina and Indonesia (northwestern Java to southern Irian Jaya) can also be classified as tropical moist deciduous forests since they contain species which are not evergreen; the forest stand is of simpler structure than rain forests with a canopy 25–30 m high and fewer emergents. Although the canopy is less dense and the number of species smaller than in tropical semi-evergreen forests, the percentage of precious hardwood species is usually higher. The composition varies; the dominant species in Indonesia are: Tectona grandis, Melaleuca leucadendron, Eucalyptus alba, Banksia dentata, Timonius sericeus, etc.
In the mixed deciduous or monsoon forests in Burma and Thailand teak is accompanied by Xylia, Pterocarpus macrocarpus, Homalium tomentosum, Terminalia, Dalbergia, Vitex, etc. In these two countries there are also extensive areas of mixed deciduous forests in which dipterocarps predominate. In Lao, Kampuchea and Vietnam the principal trees of mixed deciduous forests are Dipterocarpaceae and Leguminosae.
e) Edaphic subtypes in moist forests
- Heath forests
On soils derived from siliceous parent materials which are inherent materials which are inherently poor in bases, and commonly coarsely textured and freely draining, rain forest is replaced by heath forest which is strikingly different in flora, structure, and physiognomy.
In heath forests there are more trees with small leaves than in evergreen rain forest and many leaves are distinctly sclerophyllous (that is, thick and leathery); deciduous species are absent. The ground commonly has a bryophyte cover. Trees of large girth are rare; buttresses are smaller, but stilt roots commoner. Big woody climbers (including climbing palms) are rare, but slender, wiry, independent climbers frequent. Epiphytes are frequent and photophytes occur nearer the ground than in evergreen rain forest.
Heath forest is easily degraded by felling and burning to an open savanna of shrubs and scattered trees.
The greatest extent of heath forest in the region is in Sabah, Sarawak and Kalimantan where it occurs around much of the coastline on raised terraces. Similar but less extensive terraces which also bear, or oncebore, heath forest occur along the southern coasts of Thailand and Kampuchea. In Peninsular Malaysia, they occur on the east coast as parallel strips separated by swampy hollows and on parts of the west coast. In Borneo island lowland heath forest also occurs extensively inland, mainly on sandstone plateaus. In parts of Sarawak, mainly inland, podzolic soils become, temporarily to more or less permanently, waterlogged because of imperfect subsoil drainage or because the hard pan in the soil forms an impermeable layer. The forest here in structure and physiognomy is heath forest. Small areas of inland heath forest are reported in Papua New Guinea. Some of them carry Agathis labillardierei forest. The apparent absence of extensive areas of inland heath forest from the huge land mass of New Guinea serves to emphasize the uniqueness of Bornea island in this respect. Some 850 species of trees (428 genera) occur in the heath forests of Sarawak and Brunei; of this total 220 species also occur in lowland dipterocarp rain forest. For example, many of the Dipterocarpaceae of the Sarawak heath forest are found in evergreen rain forest, and these are found mainly in the most favourable heath forest sites. There are also 146 species common to both heath forest and peat swamp forest including several big timber trees. Heath forest also has some species in common with upper montane rain forest. Myrtaceae are a prominent family in heath forest.
- Peat swamp forests
The peat swamp forest formation is of a very special type and with a rather restricted flora. The soil is peat, usually acid with a pH less than 4.0. The surface of a peat swamp is not subject to flooding and is normally markedly convex. The peat is usually at least 50 cm deep, and depths up to 20 m have been recorded. Lowland peat swamp forest is very extensive in eastern Sumatra, on both coasts of the Malay Peninsula, and in Borneo island. It is apparently absent from eastern New Guinea despite the very great extent of fresh-water swamp vegetation there. There is some peat in the southern Philippines but not in the drier northwest. Most of the tree families of lowland dipterocarp evergreen rain forest are found in peat swamp forest; exceptions are Combretaceae, Lythraceae, Proteaceae, and Styracaceae. Palms are poorly represented. The most common dipterocarp is Shorea albida. The other characteristic species are of genera: Amoora, Anisoptera, Calophyllum, Campnosperma, Combretocarpus, Cratoxylon, Dryobalanops, Durio, Eugenia, Gonystylus, Jackia, Koompassia, Litsea, Lophopetalum, Melanorrhoea, Pandanus, Parastemon, Payena, Pholidocarpus, Ploiarium, Shorea, Tetramerista, Tristania, Xylopia and Zalacca.
In Peninsular Malaysia peat swamp forests occupy extensive areas of coastal plains and central southern parts. They are found on peat layers 1–10 m depth overlying marine alluvial clay. Species of genera Koompassia, Anisoptera, Hopea and Shorea occur here.
In Sabah peat swamps are confined to western and eastern parts of the state. Main constituent species are ramin (Gonystylus bancanus), jongkong (Daotylooladus stenostachys) and species of Shorea and Hopea.
In Sarawak peat swamp forests form some 16% of the total forest area and are commercially important. The species composition is generally the same as in Sabah.
- Littoral and swamp forests (group 4 of Champion and Seth)
These are located in tidal flats bordering coastal areas and along mouths of rivers. Humid tropical climates, high rainfall, and silt-laden rivers contribute to the formation of suitable “mud flats” on which mangroves thrive 1. Mangroves generally grow below the level of water of spring tides. Their root systems are regularly inundated with saline water. The floristic diversity of mangrove forests is low; only 50 to 90 species are represented in the region. Depending on the degree and extent of inundation the species composition in mangrove forests changes. As land builds up through accumulation of sedimants a process of succession takes place. Adaptation to shade is important for succession. Species of Sonneratia and Avicennia are typical pioneers, intolerant, of shade. Rhizophora spp. often overtop the pioneers as the land rises and shades them out. Many mangrove areas are remarkably stable and successions may go in circles with pioneers following later stages.
Extensive stands of mangroves are found in all the subregions of tropical Asia.
In south Asia, Sundarbans of Bangladesh are the largest (430 000 ha) and have a complex ecology. This unique vegetation is classified into three zones: fresh water forest (north-eastern part), moderately saline forest (eastern part) and salt water forest (western part extending into India). In the fresh water areas Heritiera fomes is the most important tree, followed by Excoecaria agallocha. Other species in the Sundarbans of Bangladesh are: Carapa moluccensis, Ceriops roxburghii, Bruguiera gymnorrhiza, Sonneratia apetala, Avicennia officinalis, etc. Grasses, Oryza coaretata and Typha elephantica are relatively abundant in the Sundarbans due to the fresh water influence. In Bangladesh besides local uses as firewood and charcoal, Excoecaria agallocha wood is used for newsprint manufacture.
In India in addition to the western fringe of Sundarbans (an extension of mangroves of Bangladesh), very rich mangroves are found in Andaman-Nicobar archipelago in the Bay of Bengal. Here Rhizophora mucronata and R. apiculata are abundant; Bruguiera gymnorrhiza and B. parviflora are important. Ceriops tagal is common as understorey. Mangroves are also found in the deltas of rivers Krishna, Godavari and Mahanadi draining into the Bay of Bengal on the east coast. They are reduced and degraded due to heavy and unregulated cutting for fuelwood and fodder. An interesting example of mangroves growing in extremely arid conditions is found in Kutch and Saurashtra areas (Gujrat state in western India). The forest here is a low scattered scrub with only one species: Avicennia marina.
In Sri Lanka about 4 000 ha of mangrove forest occurs in the Manner region and in river estuaries and lagoons. The genera Rhizophora, Bruguiera, Avicennia and Sonneratia are represented.
In continental southeast Asia (including centrally planned countries) mangrove forests are predominant in Burma, Thailand and Vietnam. In Burma the Irrawaddy delta mangrove forests are similar to those of Sundarbans of Bangladesh. In Thailand, major mangrove areas are found along the west coast of the peninsula, namely from Ranong to Takuapa and from Phangnga to Satun. A recent survey based on satellite imagery (1973) estimated the mangrove area at 312 700 ha. These are greatly affected by human exploitation and in fact vastly degraded. The production of charcoal from Rhizophora apiculata and R. mucronata was most common. A low scrub of Avicennia marina, a hardy species which coppices well, is the most common species to be found in areas near human habitation. Artificial regeneration of Ceriops tagal and Rhizophora apiculata is practised in Thailand. In Vietnam mangroves are most conspicuous in the Vung Tan area southeast of Ho Chi Minh City - along the coast of the Mekong delta. Rhizophora and Bruguiera comprise over three quarters of the mangrove forests here. In the fresh water swamps Melaleuca leucadendron is the predominant species. During the 1962–71 war about 100 000 ha of mangrove vegetation was killed by herbicides.
In the insular southeast Asia subregion, Indonesia, Malaysia and the Philippines have sizeable areas under mangrove vegetation. In Indonesia extensive areas are found in Sumatra, Kalimantan and Irian Jaya. Very little is known about the extensive swamps in Irian Jaya. Large scale exploitation of mangroves in Kalimantan and north Sumatra for production of wood chips is known since 1975. The most frequent species in these forests are: Rhizophora apiculata, Oncosperma tigillarium (nibong palm), Avicennia alba and Bruguiera parviflora. In Peninsular Malaysia mangrove forests are found near Matang, Keland and Johor Baharu. Reclamation of mangrove areas for agriculture and construction purposes is reported in Peninsular Malaysia. Rhizophora, Bruguiera, Avicennia are the common genera represented in these forests. Replanting of mangrove species (mainly of Rhizophora) is now being carried out. In Sarawak, mangrove forests cover approximately 174 000 ha and are concentrated in the estuaries of major rivers. The mangrove vegetation of Sarawak has been classified into 16 subtypes. The species represented belong to the genera: Sonneratia, Avicennia, Rhizophora, Bruguiera, Excoecaria, Nypa, Oncosperma, Heritiera and Xylocarpus. In addition to wood chips and timber there is commercial production of nipa sugar, the bulk of which is used in the production of local “whisky”. In Sabah some 350 000 ha of mangrove forests exist all along the coastline. The large mangrove forests at Cowie Harbour, Tawau consist predominantly of Rhizophora apiculata, R. mucronata, Bruguiera parviflora and Ceriops tagal.
Many of the mangrove forests of Philippines have been reclaimed for agriculture in recent years. The existing areas are mainly concentrated in Mindanao, Visayas, Palawan and north Luzon islands in that order. The species composition is similar to that found in other insular southeast Asia countries. Exploitation for firewood is most common. Replanting efforts are also undertaken. The use of mangrove forest areas for fish pond development is attracting increasing attention.
In Papua New Guinea most of the mangrove forests are almost virgin. They are found extensively along Gulf of Papua, in the Sepik and Fly estuaries. Large areas of fresh water swamp forests exist also, with Campnosperma brevipetiolatum, Terminalia brassii and Metroxylon sagu (sago palm) as main species. This latter is important as it provides staple diet to some 100 000 people. The local population use mangrove wood for construction of houses and as firewood. Young radicles of Bruguiera, fruits of Sonneratia alba and fat from Cerbera seeds are used as food, and an alcoholic drink is made from extracts of Rhizophora mucronata fruits. Nipa is used for thatch and Derris for fish poison. Proposals and surveys for starting wood chipping industry have been carried out in some areas.
f) Tropical dry deciduous forests (group 5 of Champion and Seth)
They occur in zones where the annual mean of maximum temperatures lies between 29 and 35°C and the annual mean of minima between 18 and 23°C. The rainfall may be 900–1000 mm and may even reach 1 500 mm sometimes. A pronounced dry season is common. They mostly occur on plateaux and plains. Most of these forests suffer from severe biotic interference. Fires are frequent and grazing is heavy.
In India either teak or sal predominates in some areas. The other dry deciduous species of common occurrence are: Anogeissus latifolia, Diospyros tomentosa, Hardwickia Pinnata, etc.
In Thailand dry deciduous forests occur from the plain 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. The composition of the forests is to some extent conditioned by this factor in that fire resistant species are more common in these forests. In addition to teak, Pterocarpus, Xylia, Lagerstroemia, Afzelia, etc., many species of bamboos are present in the undergrowth: Thyrsostachys siamensis, Gigantochloa albociliata, Bambusa tulda, Dendrocalamus membranaceus and others.
In Papua New Guinea deciduous forests occur as a transition between evergreen forests and the savannas in the south central coast. The forests on the coastal limestone hills near Port Moresby where the annual rainfall is less than 1 200 mm are also marked by deciduous character. The deciduous species frequently found in Papua New Guinea are: Garuga floribunda, Brachychiton carruthersii, Intsia bijuga, Protium macgregorii, Terminalia spp., Sterculia spp., Gyrocarpus americanus, Bombax ceiba, Albizia sp., Maniltoa spp., Adenanthera pavonina and Erythrina sp.
Open broadleaved forests (NHc/NHO) and broadleaved scrub formations (nH)
a) Tropical thorn forests (group 6 of Champion and Seth)
These forests are generally the result of degradation of forests due to harsh climatic and edaphic environmental conditions and excessive biotic interference. Heavy grazing, lopping and fires contribute to severe reduction in tree species, setting in of xerophytic conditions and the conversion of erstwhile wooded areas into those with isolated trees intermixed with thorny shrubs and grasses. They occupy areas having less than 1 000 mm rainfall with 5 to 7 dry months. The average temperature is generally more than 20°C. They are open low forests in which thorny species predominate. Trees usually have short boles and low branching crowns. Height is usually 6 to 9 m. This type of forest is not regarded as commercially important but it helps to supply local needs of fuelwood and fodder to a limited extent. The riverain forests of Terai region India, Nepal, and Pakistan are typical of open broadleaved formations as defined in this study. Here species like Acacia arabica, Prosopis spicigera and Tamarix sp. are interspersed with Dalbergia sissoo. Besides fire hardy species, grasses like Themeda, Erianthus and Saccharum are characteristic. In Sri Lanka savannas with a tree cover are found in the mountain zones between 500 m and 1 700 m altitude. They are characterised by a dense layer of tussock grasses. Tropical thorn forests occur on plains from northwest to southeast, generally below 300 m elevation. Both in the arid and semi-arid areas of the Indian subcontinent and Sri Lanka the most common species in this type of formation are: Acacia leucophloea, A. chundra, Carissa spinarum, Dichrostachys cinerea, Randia dumetorum, Euphorbia antiquorum, Ziziphus spp., etc.
In Thailand on shallow, often rocky and lateritic soils in the northern and north-eastern regions savanna forests and scrub formations occur. Here the soil is often covered with Imperata cylindrica and other grass species. As elsewhere in the region the scrub forests are heavily exploited for fuelwood and charcoal.
In Sabah and Sarawak scrub formations are insignificant and occur on rocky outcrops and degraded lands. In Indonesia open broadleaved forests include the natural savannas with Eucalyptus spp. Scrub formations occur near volcanio craters.
In Papua New Guinea the eucalypt savanna, the Melaleuca savanna and the mixed savannas are common types of open woodland formations. Scrub formations occur in lowland regions with strong monsoonal climate. Hibiscus tiliaceus, Desmodium umbellatum, Pluchea indica, Sinoga lysicephala, Styphelia suaveolens are the common species.
b) Dry evergreen forests (groups 7 and 10 of Champion and Seth)
These formations are constituted by evergreen species of small size trees and shrubs; they grow up to 1 000 m altitude on the hill slopes. A large part of these forests is degraded by grazing, browsing, lopping and overexploitation for firewood. These formations are commonly found in south Asia. The frequent species are: Acacia modesta, Olea cuspidata, Ziziphus jujuba, Dodonea viscosa, etc.
c) Sub-alpine and alpine scrub (groups 14, 15 and 16)
In India, Nepal, Bhutan, and Pakistan, at elevations between 3 000 m and 4 600 m in the Himalayas, an almost evergreen forest of Rhododendron mixed with some birch and other deciduous species is met with. The crop is open and stunted and of little commercial value.
Coniferous forests (NS) (group 9 and subgroups of groups 12 and 13 of Champion and Seth)
In India, Pakistan, Nepal and Bhutan coniferous forests are confined to the Himalayan region. The distribution of species depends on altitude, aspect and exposure in addition to rainfall and geology. Low altitude coniferous forests occur between 600 m to 2 300 m. On higher elevations they occupy the southern aspects. Frequent species are: Pinus roxburghii and P. insularis with an admixture of oaks. The principal commercial species in high altitude coniferous forests occurring from 1 650 m to about 3 000 m are Cedrus deodara, Pinus wallichiana, Abies pindrow, Picea smithiana, Pinus gerardiana, Juniperus macropoda and Taxus bacoata.
In Thailand coniferous forests are typically found on the sandy soils of the northern and central parts. The major coniferous species are Pinus merkusii and P. kesiya (= P. insularis). In Indonesia the only coniferous forests are Pinus merkusii stands in northern Sumatra and Agathis forests in Irian Jaya. This latter species is found also in small size patches amidst the mixed broadleaved forests in other areas such as eastern Kalimantan. Also in Irian Jaya, at elevations of about 3 500 m sub-alpine forests with stunted trees of Araucaria, Dacrydium, Podocarpus etc., which after destruction are replaced by alpine grasslands, can be found extensively. In the Philippines natural pure stands of Pinus insularis and P. merkusii are found in northern Luzon, western Luzon and the high mountains of Mindoro islands.
In Papua New Guinea conifers sometimes form pure stands or are dominant in the upper montane forests. Araucaria hunsteinii and A. cunninghamii occur in the upper lowland and montane forests. In the New Guinean montane forests conifers are frequent. Podocarpus is a common genus here.
1 Informations on mangroves given in this paragraph are extracted from “Mangrove Forest Resources and Their Management in Asia and the Far East” by B. Christensen (FAO Regional Office, Bangkok - (1979)
1.1.2 Present situation of the woody vegetation
Tables 1 deals with areas under natural woody vegetation (formations with symbols with N or n as first letter) i.e. areas where more than 10% of the ground is covered by trees which are naturally growing. Plantations are dealt with separately in section 1.2 (symbols with P as first letter). Forest areas under natural woody vegetation are broadly classified into 1:
closed broadleaved forests (NHCf)
coniferous forests (NSf)
bamboo forests (NHBf)
open broadleaved forests (NHc/NHO)
closed forest and bamboo fallow (N.a)
open forest fallow (NHc/NHOa)
shrub formations (nH).
In 1980, the total area under natural woody vegetation (i.e. all categories mentioned above including forest fallows) in the 16 countries of tropical Asia was 445 million ha or about 47% of the land surface. Indonesia, India, Burma, Papua New Guinea and Malaysia were the five largest on the basis of extent of natural woody vegetation with 158, 72, 53, 40 and 26 million ha respectively. In their declining order the areas under natural woody vegetation in million ha in other countries were: Viet Nam (21), Lao (19), Thailand (17), Kampuchea (13), Philippines (13), Pakistan (3.6), Sri Lanka (2.7), Nepal (2.5), Bhutan (2.4), Bangladesh (1.2) and Brunei (0.6).
Subregion wise, insular southeast Asia has the largest extent of natural woody vegetation, some 197.6 million ha which is 44% of the region's total. Continental southeast Asia (including centrally planned countries) accounts for some 28%, south Asia 19% and Papua New Guinea 9% of the region's total.
In the region as such, the largest category is that of the closed forests not affected by agriculture - N.f: 305.5 million ha or 69% of the total area under natural woody vegetation - followed by closed forest and bamboo fallows - N.a: 69 million ha -, shrub formations - nH: 35.5 million ha -, open forests - NHc/NHO: 31 million ha - and open forest fallows - NHc/NHOa: 4 million ha. Except for open forest fallows which are essentially confined to Indonesia, the other formations are distributed in all the countries of the region.
The countries of the region with extensive closed forests follow closely the listing for natural woody vegetation above. The proportion of closed forests to total land area is of interest. The following groups can be made:
|% of closed forests to land area||Countries/states|
|> 60%||Papua New Guinea, Sabah, Sarawak|
|50 – 60%||Brunei, Indonesia, Peninsular Malaysia|
|40 – 50%||Burma, Bhutan, Kampuchea|
|20 – 40%||Sri Lanka, Philippines, Lao, Viet Nam|
|10 – 20%||India, Nepal, Thailand|
1 See section 2.1.4 of chapter II for more details