|Man in the Mangroves. The Socio-Economic Situation of Human Settlements in Mangrove Forests (UNU, 1986, 115 p.)|
Sanit Aksornkoae. Somsak Priebprom, Anant Saraya, and Jitt Kongsangchai
Mangrove Resources in Thailand
Mangrove forests are one of the primary features of tropical and subtropical coastal ecosystems. They reach their maximum development in South-East Asia. Definitions of mangrove forest generally embody two different concepts: The first refers to an ecological group of evergreen plant species belonging to several botanical families but possessing marked similarities in their physiological characteristics and structural adaptation and having similar habitat preferences. The second concept implies a complex of plant and animal communities. In Thailand the mangrove plant community is composed mainly of Rhizophora species associated with other trees and shrubs growing in the zone of tidal influence, both on the more sheltered parts of the coast and inland, along river banks and tidally flooded parts of estuaries.
Distribution of Mangrove Forests
Mangrove forests in Thailand occur on seashores, around lagoons, and along rivers at levels between low and high tides, in the southern and southeastern parts of the country and the upper part of the Gulf of Thailand (fig. 1). The extent of existing mangrove forest in 1979, as estimated from satellite imagery, was approximately 287,308 ha, or 1,795,675 rai (Klankamsorn and Charuppat 1982). A breakdown of mangrove areas by province is shown in table 1. Out of the total, 176,653 ha (61.5 per cent) is managed by the Royal Forest Department. The remaining areas are private property, and some are classified as unproductive forests.
Species and Zonation
Table 2 lists mangrove species found in Thailand, including 27 genera of trees and other plants.
Rhizophora species are the most abundant and have the widest geographical distribution.
In most mangroves, different species dominate certain zones. The characteristic zonation pattern results from differences in the rooting and growth of seedlings and the competitive advantage each species has along the gradient from mean sea level to above the high-water line. Aksornkoae (1976) studied the dominant species associationsof mangrove vegetation in south-eastern Thailand and summarized the variation in mangrove vegetation from the river edge to inland sites. Rhizophora apiculata and R. mucronata are the dominant species along river and channel banks. Avicennia and Bruguiera are associated with Rhizophora along the channels, but form a distinct zone further inland. Xylocarpus and Excoecaria dominate on sites adjacent to the Avicennia and Bruguiera zone that have drier soils and are less subject to tidal inundation; Ceriops and Lumnitzera are also found within this zone. Melaleuca reaches its greatest dominance further inland on even drier and more elevated sites that are still less subject to tidal flooding. The fern Acrostichum aureum occurs throughout the mangrove area but is densest in sites that have been disturbed.
FIG. 1. Distribution of mangroves in Thailand
TABLE 1. Area of mangrove forests in Thailand by province, estimated from 1979 Landsat satellite imagery
|Region and province||Area |
|rai||% of |
|Upper Gulf of Thailand (southern Chao Phya plain)|
Source: Klankamsorn and Charuppat.
TABLE 2. Mangrove species of Thailand
|Rhizophoraceae||Rhizophora apiculata, R. mucro|
|nata, Bruguiera cylindrica, B.|
|parviflora, Ceriops roxburghiana,|
|Sonneratiaceae||Sonneratia caseolaris, S. alba|
|Verbenaceae||Avicennia alba, A. officinalis,|
|Meliaceae||Xylocarpus obovatus, X. moluc|
|Caesalpiniaceae||Caesalpinia didyna, Intsia retus|
|Palmae||Nypa fruticans, Phoenix paludosa|
|Acanthaceae||Acanthus ebracteatus, A. ilici|
|Pteridaceae||Acrostichum aureum, A.|
|Rubiaceae||Litosanthes biflora, Scyphiphora|
|Malvaceae||Hibiscus tiliacaus, Thespesia|
Human Settlements and Populations in Mangrove Areas
Thailand has a total of about 2,600 km of coastline, of which 927 km are lined with mangroves (KIankamsorn and Charuppat 1982). People who live in or earn their living from the mangroves use the zone for timber, poles, fuelwood, and thatch, for capture and culture fisheries, for salt production, and for other purposes.
It is difficult to estimate how many people are dependent on this resource. Unpublished data collected by the Royal Forest Department show the average number of persons working in the concession forests is 3.7 per km² and the number of people living in and adjacent to the mangroves is about 34 per km². It is estimated that about 98,000 people live within and near the 287,308 ha of mangroves. Of these, 8,375 work in the 176,653 ha of concession forests.
Most mangrove dwellers live in clustered houses in small village communities at the edge of the forest or along channels within an estuary. Most of the villagers are of Thai origin; other ethnic groups include Muslims speaking a Malay dialect, and Chinese.
The villages can be classified into three main types: island villages, shrimp-pond villages, and coastal-land villages. Most of these villages comprise 20-50 households, with populations of 10-300, but larger villages may incorporate more than 100 households and a population of 600 (Petchmedyai 1980).
Traditional Uses of Mangrove Resources
The traditional uses of mangrove wood in Thailand are for charcoal and firewood, poles and construction materials, fishing gear, tanning, and medicines. In addition, there has been some distillation of chemical products from mangrove wood. The palm Nypa fruticans provides materials for several purposes.
Charcoal. About 90 per cent of the wood harvested from mangrove forests is used for charcoal production. Various species of the Rhizophoraceae can be used to make charcoal, but Rhizophora apiculata and R. mucronata, which produce heavy, dense, hard charcoal with a high calorific value that is almost smokeless when burned, are preferred. Other species, such as Bruguiera spp. and Ceriops sp., are also used but in minimal quantity. The minimum size of stems for charcoal burning is about 5 cm. The average harvest is about 783,780 m³ of wood per year, which produces about 387,800 m³ of charcoal -or about 263,704 metric tons on the basis of 680 kg per cubic metre (Phuritat 1975). This charcoal is produced in 1,273 kilns located in or near the mangrove areas. Typical charcoal kilns are domeshaped, made of clay and bricks, and have a capacity of between 50 and 200 m³. The average amount of wood used, number of kilns, and charcoal production in different parts of the country under five regional forest management offices are shown in table 3. Charcoal produced from mangrove wood is used in Bangkok and coastal towns, in addition to which a surplus is exported to neighbouring countries.
Firewood. Wood from mangrove forests is also widely used by mangrove dwellers and people who live along the coastline as firewood. No data are available on the amount of firewood consumed per year per species. The mangrove species commonly used for firewood are Avicennia, Xylocarpus, Excoecaria, Bruguiera, and Lumnitzera spp. Rhizophora spp. are also used for firewood but only in small quantity because these species are preferred for charcoal.
Poles. Mangrove poles are used for many purposes where water-resistance is needed -especially for foundation pilings, ore-rinsing troughs, and fishing stakes. The quantity of wood used for these purposes is minimal, however, and no data are available on the total amount. Mangrove species commonly used for poles are Rhizophora apiculata, R. mucronata, Ceriops sp., Bruguiera spp., and Excoecaria agallocha. Excoecaria agallocha seems to be more widely used than the others.
TABLE 3. Production of charcoal from mangrove wood in Thailand, 1978-1982
|Songkla||51,041||1,701||181,886||451||120- 170||4- 5||90,943|
Source: Royal Forest Department.
a. With 30-year rotation.
Construction materials. Mangrove lumber is used for house construction mainly by people who live in or close to the mangrove forest. Wood of various mangrove species can be used for different parts of the house. Rhizophora, Avicennia, Bruguiera, and Xylocarpus are commonly used for columns, bracing members, beams, and roof frames. Floors and platforms are made only of Rhizophora and Bruguiera species. Unfortunately the quantity of mangrove wood used for construction has not been recorded.
Fishing gear. Various types of fishing gear are used by mangrove dwellers, and some of the equipment is made of mangrove wood. Poles from Rhizophora spp. are usually used for crab traps. The crab most commonly caught in the mangrove area is Scylla serrate. Drift gill nets and winged set bags also use mangrove poles; Rhizophora apiculata and Bruguiera spp. are the species commonly used for this purpose. The volume of wood used for fishing gear is small.
Tanning. Mangrove bark is now only rarely used for tanning in Thailand. Formerly tannin from Rhizophora and Ceriops was used by fishermen for dying their fishing nets, but now they mainly use nylon nets, and little tannin is used for dyeing nets.
Medicines. Mangrove dwellers in Ranong Province, on the west coast, have reported that they commonly use various mangrove species for medicines. Acanthus ebracteatus and A. ilicifolius are used to treat kidney stones, Bruguiera parviflora is used to relieve constipation, Avicennia alba and A. officinalis are used to treat thrush in children, and Triumfetta rhomboidea is used for menstrual fevers (see ch. 3, below, for details).
Distillation. The only plant for wood distillation in this part of the world is at Kapur, near Ranong. Raw distillate from mangrove wood (Rhizophora apiculata), consisting essentially of pyroligneous acid, is collected from the vents of a charcoal kiln by condensation. This condensate can be fractionated by a complicated process, producing 5.5 per cent acetic acid, 3.4 per cent methanol, and 6.5 per cent wood tar. At present, however, problems with the extraction technique make the process uneconomical.
Nypa fruticans. The nipa palm, Nypa fruticans, which is widely distributed in the mangrove area, is used for a great variety of purposes, the chief one being the use of its leaves for thatching. Nipa leaves are also popularly used locally for cigarette wrappers. Elsewhere, alcohol is extracted from nipa sap, but this is not done in Thailand.
Fish production includes capture and culture fisheries.
Capture fishery. More than 1.7 million metric tons of marine fish and crustaceans were caught in Thailand from 1979 through 1980(table 4). Of this amount, almost 120,000 tons were shrimp, which fetch the highest price per kilogram and are often most abundant in or adjacent to mangrove areas. Of the total shrimp production, about 6 per cent was from coastal aquaculture (much of it in mangrove zones), 22 per cent from small-scale fishing (mostly mangrove capture fishery), and 72 per cent from large-scale fishing (mainly off-shore operations). Many of the shrimp from large-scale fishery are mangrove-dependent species (e.g. Penaeus merguiensis, Metapenaeus spp.). The degradation or reduction of mangrove areas could adversely affect the coastal fisheries, particularly the capture of shrimp (Martosubroto and Naamin 1977; Gedney, Kapetsky, and Kuhnhold 1982).
Culture fishery. Of the total marine shrimp production in Thaiiand in 1979, about 6 per cent, 7,000 tons, was from coastal aquaculture (see table 5). Most of the aquaculture farms in Thailand, particularly shrimp farms, are in the mangrove forest zone in Samutsakorn, Samutsongkram, Samutprakarn, Surat Thani, and Nakornsrithammarat provinces. About 62,400 ha of the total mangrove forest area in Thailand is suitable for shrimp aquaculture (National Research Council of Thailand 1977). The 7,000 tons of shrimp produced in1979 came from 3,378 farms, occupying a total area of about 24,675 ha. Production was thus only about 284 kg per hectare. This low figure suggests that most of the farms are not very productive. In general they have been found to be productive only for the first three or four years of operation and are often abandoned after that. This practice is inefficient and very wasteful, resulting in the degradation or destruction of large areas of mangroves, and may in turn adversely affect the yield of coastal shrimp capture.
TABLE 4. Marine fishery production in Thailand, 1974-1980 (metrics tons)
|Total production||Marine shrimp|
|1974 - 1976||1,432,663.3||85,268.0|
Source: Chaitiemvong 1983.
TABLE 5. Shrimp culture production in Thailand, 1974-1979
Production (metric tons)
Source: Chaitiemvong 1983.
TABLE 6. Mangrove destruction in Thailand, 1961-1979
Extent of destruction
|Total||Average per year|
a. Sukwong et al. 1976.
b. Vibulsresth, Ketruangrote, and Sriplung 1976.
c. Klankamsorn and Charuppat 1982.
The Destruction of Mangroves
Factors Leading to Destruction
Population increase, aquaculture, mining, salt ponds, and the over-exploitation of mangrove forests without replanting are important factors leading to the progressive destruction of mangrove forests.
Rapid increase of population. During the years 1950-1981, the population of Thailand grew at an average annual rate of about 2.7 percent. The rate of increase is now below 2 per cent as a result of family planning programmes. Population growth led to urban expansion and to increased demand for agricultural land. Since upland and lowland areas were already occupied, large numbers of people have moved to coastal areas, including mangrove forest areas, but no data are available on the size of the areas affected.
Aquaculture. Aquaculture, especially shrimp and fish farming, is widely practiced in the mangrove area. Shrimp and fish ponds have been built by clear-cutting the mangrove forest, levelling, and building embankments. The area of shrimp farms increased from 12,867 ha in 1,568 farms in 1975 to 24,675 ha in 3,378 farms in 1979 (table 5), not including areas converted to aquaculture and then abandoned without replanting.
Mining. Hydraulic tin mining in the mangrove area has been carried out mostly in Ranong, Phangnga, and Phuket provinces. Mining results in the deposition of large quantities of silt in stream channels and in the intertidal and near-shore zones. The extent of tin mines in the mangrove forest was approximately 926 ha in 1979 (Klankamsorn and Charuppat 1982), but the area affected by siltation from tin mines was much larger than this.
Salt ponds. Large areas of mangrove forest, totalling about 10,356 ha, have been converted to salt ponds. Most of these are located in the upper parts of the Gulf of Thailand.
Over-exploitation for forest products without replanting. In various parts of the mangrove forests, trees have been cut at a rate beyond their ability to regenerate. After cutting, some mangrove areas have been left without replanting.
Rate of Destruction
During the period 1961-1979 the total area of mangrove forest converted to various purposes was about 80,592 ha (Klankamsorn and Charuppat 1982). Table 6 shows that the rate of destruction of mangrove forests was high from 1975 to 1979, about 6,348 ha per year, as compared with 3,943 ha per year from 1961 to 1975.
Case Study: The Socio-economics of Mangrove Forest Dwellers in Ranong Province
The rapid decline and deterioration of mangrove ecosystems in Thailand under stress from population growth and economic development, to which scientists and conservationists have called attention, implies the need to recognize the importance of conservation, management, and restoration of mangrove forests so that productivity may be optimized and the best economic yield obtained on a longterm basis without destroying the mangrove ecosystem. Several organizations, especially the Royal Forest Department, have encouraged scientists to develop management plans for the maximum and efficient use of mangrove resources. Future management plans for mangrove forests will also emphasize the improvement of the quality of life of mangrove dwellers.
One major constraint on development of a mangrove management plan for improving the quality of life of mangrove dwellers is lack of basic knowledge about community structure, resource utilization, and economic conditions of people living in mangrove communities. It is therefore necessary to make intensive studies of mangrove settlements, which depend mainly on the productivity of mangrove organisms. Decisions on the future use of mangrove ecosystems based on inadequate knowledge of these people may result in unanticipated hardship for mangrove dwellers, and irrevocable loss of valuable mangrove resources.
To obtain basic knowledge of mangrove communities, the United Nations University supported a research project on the socio-economics of dwellers in mangrove forests. Field study was carried out from September 1983 to June 1984 in the villages of Ko Lao and Had Sai Khao, both in Ranong Province in southern Thailand.
The main objectives of the research project were:
- to study the sociological characteristics of mangrove dwellers,
- to study the household economics of mangrove dwellers,
- to evaluate socio-economic changes and the quality of life of mangrove dwellers,
- to study and evaluate differences in lifestyles in communities of mangrove dwellers with different cultural-religious backgrounds, and
- to provide baseline data for developing a mangrove management plan in order to improve the traditional way of life of mangrove dwellers.
Selection of the study area. Ko Lao and Had Sai Khao villages were chosen as study sites for several reasons. They provide good examples of different groups of mangrove dwellers. In Ko Lao the villagers include both Muslims and Buddhists, while in Had Sai Khao they are exclusively Budhists. Each village has 26 households. The villages are about 4 km apart, on the shores of the Ranong estuary.
Collection of data in the field. Data were gathered by means of interviews. A questionnaire and a survey of socioeconomic characteristics included household size and composition by age, sex, education, occupation, and religion; mobility and land tenure; consumption of forest products; fishery production; and health and sanitary conditions. Representatives of each household, generally the heads of the families, were interviewed by graduate students who lived in the villages for various periods. Great care was taken to establish rapport and to convince the interviewed persons that the results of this study would be used in revising the mangrove management plans and other mangrove activities and that this would improve their traditional way of life. Our impression is that the interviewed persons provided as accurate information as they possibly could.
FIG. 2. Location of Ko Lao and Had Sai Khao villages
Data analysis. Numerical and percentage frequency distributions were computed from field survey data for each village in order to describe socioeconomic characteristics such as age, sex, education, and occupation. Data on economic conditions were analysed in relation to sources of income and expenditures. Other information such as health and sanitary conditions, daily life, and perceptions regarding use and conservation of mangrove resources were also analysed. These tabulations allowed comparison of life-styles of population groups with different religions.
General Description of the Study Area
Location. Ko Lao and Had Sai Khao villages are located at latitude 9°50' N and longitude 98°35' E, about 10 km southwest of Ranong city and about 650 km south of Bangkok (fig. 2). Ko Lao is in Paknam commune (tambol) and Had Sai Khao is in Ngao commune, both in Muang district (amphoe) in Ranong Province (changwat). The two villages are located along the coastline of the Ranong estuary, fringed by mangrove forests (fig. 3).
TABLE 7. Climatological data from Ranong Province, 1951-1975
|Temperature (°C)||Monthly rainfall (mm)||Rainy days||Relative humidity (%)||Cloudi- ness (okta)||Days with haze||Days with fog||Visi- bility (km)||Pre- veiling wind||Wind velocity (knots)|
Source: Sarigabutr et al. 1982.
Climate. The climate is humid tropical. There is little variation in mean monthly temperature, with the values between 25.5° and 28.3°C. Annual rainfall is about 4,320 mm, the highest in Thailand. Most of the precipitation falls during the rainy season, from April to November. There are about 204 rainy days per year. A summary of climatological data for Ranong Province between 1951 and 1975 is shown in table 7.
The mangrove forest. A Mangrove Research Station was established in 1983 about 4 km from Ko Lao and 3 km from Had Sai Khao, and since then the forests have been reserved for research. One concession for forestry, based at Ngao, about 10 km from the research area, had been granted before the research station was established. That area is now reserved for ecological studies of the mangrove ecosystem. Because of selective cutting in this mangrove forest for many years in the past, the forest is composed mainly of small, closely spaced trees. The average stem volume of this forest is only about 10 m³ per ha (Kooha 1983). Only parts of the forest, particularly those near Had Sai Khao village, are composed of large trees, especially Rhizophora apiculata and Bruguiera gymnorrhiza, with a diameter at breast height exceeding 60 cm and an average stem volume of about 120 m³ per ha (Jintana et al. 1983) (fig. 4)
The mangrove forests around Ko Lao and Had Sai Khao generally show a diversity of species with clear zonation (Aksornkoae et al. 1982; Miyawaki et al. 1983). Rhizophora spp., especially R. apiculata and R. mucronata, grow mainly along side creeks. Locally, along the seaward edge where the soil is sandier, the Rhizophora community is found behind the Avicennia and Sonneratia zones (fig. 5). The common species of Avicennia are A. alba and A. officinalis. Sonneratia alba is present in this area rather than S. caseolaris. Bruguiera spp., especially B. cylindrica and B. parviflora, are commonly found behind the Rhizophora community. Ceriops, particularly the C. saga/ community, grows on more elevated inland sites, and Xylocarpus, especially X. granatum, is found scattered within the Ceriops community.
Research Results and Discussion
The three main uses for mangrove wood by residents of Ko Lao and Had Sai Khao are as fuel (firewood and charcoal), for fishing gear, and for house construction.
Most Ko Lao villagers (92 per cent) used firewood for cooking, and about 58 per cent supplemented it with charcoal (fig. 7). The average household consumption of fuelwood (firewood and charcoal) in Ko Lao was estimated to be 2.72 m³ per year (table 8). The Muslims used less wood (including charcoal) for fuel than the Buddhists, the average amounts being about 2.10 and 3.33 m³ per household per year respectively. The average household consumption of firewood in Ko Lao was about 1,448 sticks, or 1.8 m³, per year. (The firewood sticks used by the Buddhist villagers are about 40 cm long and 6 cm in diameter, whereas the Muslims use a smaller size, 4 cm in diameter.) Charcoal consumption per household was 0.58 m³, or 341 kg, per year. All the charcoal used in the village is bought in Ranong or in neighbouring villages, especially Had Sai Khao, where it is produced.
TABLE 8. Estimated consumption of fuelwood per household by residents of Ko Lao and Had Sai Khao
(m³ per year)
|m³ per |
|kg per |
|kg per |
|m³ per |
|m³ wood |
|Had Sai Khao||0.6||200||0.32||1.9||680||1.0||1.7||2.02|
Most Had Sai Khao villagers used locally produced charcoal for cooking. The charcoal is made in small masonry or earthpit kilns (figs. 8-10). The average consumption of charcoal per household was 1 m³, or 680 kg, per year - about twice the amount used in Ko Lao (table 8). Most of the firewood used in Had Sai Khao is burned in order to get rid of mosquitos and other insects; consumption was only about 200 sticks, or 0.3 m³, per household per year. The average total fuelwood consumption per household in Had Sai Khao was about 2.02 m³ per year.
Some of the several types of fishing gear used by Ko Lao and Had Sai Khao villagers are made of mangrove wood. Poles from Rhizophora and Bruguiera spp. are used for crab traps. The amount of wood used for this equipment is minimal, because only small poles, about 3-5 cm in diameter and 3-4 m long, are used (see fig. 1 6). About 60 per cent of Ko Lao households use crab traps, with about 30 traps per household. About 70 per cent of Had Sai Khao households use crab traps, with each household having 30-50 traps. The quantity of mangrove wood used for crab traps was estimated to be 0.10-0.3 m³ per household. Posts made from Rhizophora apiculata and Bruguiera spp. are also used for drift gill nets. One type of fishing equipment that uses a lot of mangrove poles is the winged set bag, but this type of equipment was rarely seen in these two villages. It can be concluded that the volume of wood used for fishing equipment in both villages is small.
The typical houses of Ko Lao and Had Sai Khao villagers are very similar (fig. 11). Most houses have a bedroom, a living room, and a kitchen, with platforms in front of and behind the house. The platform behind the house is generally used for drying prawns, fish, and shrimp paste. Roofs are usually made of nipa leaves, walls of bamboo, floors and platforms of mangrove wood. A few houses in Ko Lao and Had Sai Khao have floors and/or walls and/or platforms made of wooden planks, and roofs of zinc-coated corrugated iron. Mangrove species commonly used for house construction are shown in table 9.
TABLE 9. Common mangrove species used for house construction in mangrove villages
|Columns (posts)||Rhizophora apiculata |
|Bracing members||Rhizophora spp.
|Beams (girders) and subflooring||Rhizophora spp. |
frame, partition frame, |
floor, and platform (wooden
|R. apiculata |
One Ko Lao house was measured to estimate the quantity of wood used in construction. This house was 4 x 4 m and comprised a bedroom, a living room, and a kitchen, with platforms in front (2 x 4 m) and behind (3 x 6 m). The roof was made of nipa leaves, and the walls were bamboo. Two Had Sai Khao houses were also measured. The first house was rather big, about 8 x 6 m, and comprised a bedroom, a big living room, and a kitchen, with a platform in front (4 x 8 m). The roof was made of corrugated iron, and the floor and walls were of planks. The other house was smaller, about 6 x 5 m, comprising a bedroom, a living room, and a kitchen, with a front platform (6 x 4 m). The roof was made of nipa leaves, and the walls were bamboo. The total amount of wood used to construct the house in Ko Lao was estimated at about 9 m³, the larger Had Sai Khao house 19 m³, and the smaller Had Sai Khao house 11 m³ (table 10).