5. Ecological valuation of the study areas

5. Ecological Valuation of the Study Areas

In order to assess the possible environmental hazards with regard to future developments in chemical pest control in the regions concerned, the ecological characteristics of the areas should be considered in more detail. In this chapter first a brief description will be given of the vegetation of b o t h regions. Thereafter the ecological values and functions of the main groups of ecosystems will be discussed and finally some of the natural resources will be considered in more detail such as protected areas and aquatic ecosystems. 5.1. Types of Ecosystems

West Africa The natural environment in West Africa is largely influenced by human activities. Through the centuries agriculture has been practised almost everywhere, including the cultivation of crops as well as animal husbandry. An important aspect o f human activities is the traditional burning o f the savannas. Especially in the course o f the present century the human influence on the natural environment has increased continuously as a result o f population pressure and modern technology. In the West African environment a large variety of ecosystems can still be distinguished. This variation reflects marked differences in climate over a relatively short distance o f 1200 km in the n o r t h - s o u t h direction (see Fig. 3 and Map 4). The coastal zone receives an annual rainfall of 1200 to 3000 mm pex year. There is no distinct dry season and temperatures are high with little fluctuation throughout the year. In this hot and constantly humid climate, growing conditions are favourable all year round. The natural vegetation type of this zone is the tropical rainforest. Some types are evergreen, b u t deciduous species appear in the more humid disturbed forests and their numbers increase in zones with decreasing rainfall. Possibly the semi-deciduous, drier rainforest type is completely secondary, regenerated after previous agricultural activities. On temporary or constantly inundated sites, the forest takes the form of a swamp forest. This type can be found along the coast, especially in Nigeria, Ivory Coast and also in Sierra Leone and Liberia (IUCN 1978a, 1979a). Mangrove forests are low to medium height evergreen forests confined to m u d d y tidal flats at Vol. 4 (1984) Supplement No. 6

the mouths of rivers and sheltered coasts in high rainfall regions, that are regularly inundated by salt or brackish water. Mangroves are found along the West African coastline from the Senegal estuary southwards and eastwards (Saenger et al., 1983). To the north of the tropical rainforest zone rainfall diminishes gradually and the climate becomes more seasonal. North of the rainforest zone a vegetation type is found which is commonly described as savanna woodland, characterized by drought, resistant deciduous tree species, perennial grasses and shrubs. Further north the landscape changes into a savanna type which is generally called the Sahelian savanna. Trees and shrubs disappear and among the grasses annuals become more important than perennials. Finally the landscape turns into desert environment characterized by very sparse vegetation and oases in places where water is available through natural or artificial wells. An important element of the African environment is its inland water system, tn the rainforest zone the water level in the rivers fluctuates twice a year, according to rainfall conditions. With increasing latitude, rainfall becomes increasingly seasonal, leading to annual flooding o f the rivers. Much of the surrounding savanna land is flat and the rivers may inundate immense areas. These so-called floodplains are interspersed with creeks, pools and swamps, some of which retain water throughout the year. On the soils that are periodically or permanently inundated, a semi-aquatic vegetation with grassland mosaic develops, sometimes with widely spaced trees. This type of vegetation is found for instance on the floodplains of the Central Delta o f the Niger River in Mali, around Lake Chad and its tributaries and in the Djoudj in Senegal (IUCN, 1979a). Especially in the arid savanna zones the floodplains form the main resource for agricultural development. Many o f the rivers in the savanna zone were originally bordered b y gallery forests o f varying width. In the more densely populated areas this forest type is often very much degraded or has disappeared completely. Many natural and man-made lakes form part of the watersystem. Lake Chad, on the border of Nigeria, Niger and Chad, is very sensitive to climatic variations. During the last decennium the lake has shrunk to a 'small phase', with no 49

water in'Nigeria and a seasonal marsh in Niger (Chouret, 1978). The water level in Lake Guiers in Senegal changes with the level of the Senegal River to which it is connected by a channel. In the northem part of the Central Delta of the Niger there is a group of lakes, of which the water level rises and falls with the seasonal flooding of the Niger River (Welcomme, 1972). In many rivers dams have been constructed to form reservoirs for hydroelectric and agricultural purposes. Lake Kainji on the lower Niger River (Nigeria) and Lake Volta in Ghana are the largest, but there are smaller reservoirs in Guinea and Ivory Coast (e.g., Lake Kossou, Lake Ayame) and many more are planned (e.g., on the Senegal River). Consequently the water regime in these rivers becomes fully dependent on the regulation of the outflow of these lakes, and combined with the dams and dikes built on the floodplain for agricultural purposes, the annual dynamics of flooding and subsiding are ruled out over extensive areas. On the coast the river water may pass through estuaries, tidal creeks, marshes and lagoons that are more or less brackish, before reaching the ocean. Continental Southeast Asia

The natural vegetation type of continental Southeast Asia is forest and this still covers the greater part of the landscape. The region lies mostly between 10 °N and 22°N (Peninsular Thailand reaches 6 °N, Upper Burma 18 °N). At these latitudes there is a marked seasonality in climate (perhumid to seasonally dry, see Fig. 4), entailing big seasonal variations in day length, increasing northwards. The region spans tropical, subtropical and temperate climatic zones. Elevations and mountainous areas influence the climate and there is a wide range in types of rocks and soils. This combines into a rich and varied flora and fauna mixture of continental South Asian and Malayan species, and relict species. There is a long.human history in the region, and like in West Africa most parts of the environment are strongly influenced by man, for instance most of the forests are of a secondary nature due to the previous history of shifting cultivation. Open monsoon and savanna forests and grasslands are all maintained in varying degrees by fire. No attempt will be made to describe the highly complex mosaic of forest types with an apparently infinite diversity of intermediates (see IUCN, 1976). Rainforest occurs only in the wettest places and is not very extensive. Tropical lowland evergreen rainforest occurs on the western slopes 50

of the mountains onshore from the Bay of Bengal in Burma, and along the southern wall of the mountains of Upper Burma. The tropical semievergreen rainforest is the most extensive lowland rainforest formation and is found in all the countries on the continent. Tropical lower montane, upper montane and (sub)alpine forests may form mosaics with the related monsoon types on seasonally dry mountains. These types of forest occur in Vietnam and Laos. Mangrove forest is most extensive in the deltas of the Irrawaddy and Mekong Rivers, but the mangroves occur also along the coast of Burma, Thailand, Cambodia and Vietnam (see Map 9). In Indochina in many areas mangroves and other forest types have been destroyed during wartime, not least by the use of defoliants. Freshwater and seasonal swamp forests are common in Southeast Asia (see Map 9). Examples are the seasonally inundated forest around Lake Tonle Sap in Cambodia, the swamp forests in Thailand in the vicinity of the Chao Phraya and on depressions in the peninsular region. Sandy terraces which bear or bore heath forests occur along the south coasts of Thailand and Cambodia and in the far south of Peninsular Thailand. Monsoon forests are the most extensive types of forest in continental Southeast Asia, belonging to either the tropical moist deciduous or tropical dry evergreen forest formation. The two formations often merge into each other and into savanna forest. According to the altitude they may be classed as lowland or montane monsoon forest. Savanna forests are possibly mainly derived by fire from monsoon forests, and occur as pockets in the latter. They are very extensive in Cambodia, Laos, (Northeastern) Thailand, and the central plain of Burma, possibly because of the long human intervention. Savanna forest may be degraded further to grassland (see Map 9). Alluvial valley floors which once bore riparian forest, swamp forest or herb swamps have largely been converted to rice paddies (IUCN, 1976, 1978a). The mountainous character of the region combined with a high precipitation accounts for the large number of rivers in the area, the main river basins being the Irrawaddy, Salween, Chao Phraya, the Mekong and the Red River, that all form wetland areas and deltas at their lower ends. The Irrawaddy and Mekong are floodplain rivers and paddy fields and fish ponds are found alongside these rivers. Many of the rivers have been regulated for the purpose of irrigation and the generation of electricity, which appears to have an adverse effect on the formerly important The Environmentalist

inland fisheries. Some compensation is to be found in the man-made lakes and impoundments. An important natural lake is The Great Lake (Tonle Sap) in Cambodia, which is connected with the Mekong River. When the Mekong floods, the water floods back into the Great Lake, where in turn the water level rises. In Thailand the lake Bung Boraphet is considerably reduced in size due to encroachment by rice cultivators. The lake Thale Noi (freshwater), connected by a narrow channel with the Songkhla Lake (salt water), is the most important of the system of estuaries and mangroves on both sides of the Peninsula. Other important marine biotopes are mudflats, at the lower seaward end of mangroves. These are important breeding grounds for a large number of marine species of high economic value like mussel, cockel, oyster, green mussel, shrimps, mullet, sea bass, blue crab (IUCN, 1979b). Coral reefs can only develop and thrive under relatively limited environmental conditions: tropical water temperatures, clear water, and ocean-like salinity. The complex community of coral building animals, plants, invertebrates and fish is very susceptible to changes and their habitat suffers from degradation in many places. In Southeast Asia coral reefs are present on the West Coast of the Peninsula, in the Andaman Sea, and in many areas along the coast of the Malesian Archipelago (Salvat, 1978).

On the low lying areas freshwater forests and peat swamp forests occur. On muddy coasts regularly inundated by the sea, mangroves are found (see Map 9), whereas on muddy estuaries that are periodically inundated by seawater, Nipa swamp forest (dominated by the palmtree Nipa fruticans) may grow. All islands west of and including Palawan (Philippines), Borneo and Bali lie on the so-called Sunda Shelf and formed part of mainland Southeast Asia until geologically recent times and the fauna belongs to the Indo-Malaysian faunal region. Irian Jaya lies in the Australasian region, while Sulawesi, Maluku and the eastern Nusa Tenggara form an intermediate zone where both these faunas become attenuated but meet and mix. Thus the fauna on the islands is very rich and complex and interesting from a zoo-geographical point of view. A great number of endemic species has evolved, some through longer isolation on the first islands to become separated and others through adaption to fill vacant niches on islands not reached by their competitors. At present many of these endemic species are in danger of becoming extinct. In particular species that used to live in primary forests are in danger due to the widespread disappearance of their habitat, especially species that do not succeed in adapting to living in secondary forest or in croplands (IUCN, 1976).

Malesian Archipelago A range of mountains runs from the Western shores of Sumatra through Java and Nusa Tenggara, which contains many extinct and some active volcanoes. Borneo and Peninsular Malaysia are mountainous in the centre, Sulawesi and the Philippines are mountainous throughout and Irian Jaya contains some very high mountain ranges. In contrast, the eastern half of Sumatra, southern and eastern Borneo, the southwestern side of Irian Jaya, some river valleys in Mindanao and Luzon (Philippines) and the west and south shore of Peninsular Malaysia are low lying and swampy. Most of the Malesian Archipelago was originally covered with rainforests. However, a dry climatic zone extends from north to south from Eastern Philippines through Sulawesi, Eastern Java, Bali and most of the Nusa Tenggara (see Fig. 4) which results in the appearance of drier forms of forest and some savanna in that region (see Map 9). Much of the lowland rainforest and mountainous vegetation is being degraded by logging, shifting agriculture and settlements, resulting in secondary forests or upland grasslands. Vol. 4 (1984) Supplement No. 6

5.2 Functions of the Ecosystems in West Africa and Southeast Asia In Section 1.2 a system of ecosystem function classification was mentioned in order to clarify the value of ecosystems for human society. In this chapter the functions of the main groups of ecosystems in the two areas West Africa and Southeast Asia will be described in more detail. (The main sources are IUCN, 1976, 1978a, 1979a.)

Tropical forests Biotic production functions: wildlife, birds, plants, timber, subsistence products like honey, medicinal herbs, resins, spices. Agricultural production functions: timber, oil palm, rubber, cocoa, coffee, kola, citrus, mango. Carrier functions: settlements, local forestdwelling people, recreation. Information functions: lowland forests are among the most diverse and complex ecosystems on earth; reservoir of genetic diversity, endemic plants and animals, research area for many aspects of evolution. 51

Regulation functions: large vegetation mass filters the air, global O2/CO2 balance, buffering of climatic variations, water catchment, watershed protection (control of erosion and water discharge, downstream flood protection). Tropical forest includes the Guinean and Congolian dense humid and semi-evergreen lowland forest in West Africa, the lowland Dipterocarp forest of Peninsular Malaysia, Sumatra and Kalimantan and the lowland rainforest which occurs throughout Southeast Asia. The list also represents the functions of the montane and transition forests that grow on the mountains and high plateaus in both regions.

pH, but in peat swamp forests high-acid soil conditions, with related soil-microbial processes. Regulation functions: flood regulation, microclimatic influence, reception and supply of silt load in water. This type includes the Guineo-Congolean swamp forest which is found in Ivory Coast and Nigeria (see Map 4) and the swamp forests in the vicinity of big rivers, e.g., the Mekong in Thailand, Pahang in Malaysia. Peat swamp forests are very extensive in coastal areas in east Sumatra, Peninsular Malaysia, Kalimantan, Sabah, Brunei and especially in Sarawak, where it covers 12 percent of the land area (see Map 9).

Coastal swamp forests

Inland

Biotic production functions: fish, shellfish, crustaceans, spawning ground and nursing area for fish, producer of organic materials (nutrient supply), hunting area (birds, wildlife, e.g., manatee), wood production for timber, fuel, supply of glue, fiber, dye, tannins, wax, food, drugs, beverages, honey (mangroves), supply of Nipa palm products, e.g., leaves as thatching material, edible seeds (Nipa swamp forest). Agricultural production functions: aquaculture ponds (fish, crabs, prawns, molluscs), grazing ground, rice cultivation. Carrier functions: waste disposal, catchment zone for oil and other hazardous chemicals; industrial and urban developments, harbours etc. Information functions: refugium for many land and marine species of animals (sea turtles, manatee, dugong, white dolphin, waterfowl, wide variety of vertebrate species). Regulation functions: coastal protection, bartier between salt- and freshwater habitats, supplier of nutrients for sea fish production. Mangroves are widely distributed on the coasts of the Southeast Asian continent and islands and along the West African Coast (see Maps 4 and 9). Nipa swamp forests are extensive along the coasts of the Peninsula, Sumatra, Sarawak, Sabah, Kalimantan, Sulawesi, Maluku, Nusa Tenggara and Irian Jaya. Freshwater swamp forests

Biotic production functions: wood production for timber, matches, charcoal, copal, sago, palm, wildlife; outflow of organic nutrients during floods. Agricultural production functions: rice cultivation, cattle grazing. Carrier functions: water regulation constructions, dams, irrigation schemes, water reservoirs. Information functions: wildlife and rare freshwater species, waterfowl. Soil water usually high 52

waters (rivers and lakes, floodplains, swamps and marshes) Abiotic production functions: water supply for consumption for humans, animals and plants (irrigation). Biotic production functions: high productivity of fish, shellfish, prawns; snakes, crocodiles, turtles, manatee, waterfowl, migratory birds, game etc. Agricultural production functions: aquaculture (fish ponds), rice cultivation (floating rice), (floodplains) recession or drawdown agriculture, grazing. Carrier functions: water regulation constructions, dams, hydro-agricultural-electric reservoirs, transport medium, navigation; dumping and drainage of waste; substrate-linked and landscape recreation (game). Information functions: research on ecological theories; education, characteristic flora and fauna, including migratory birds, wildlife in general; reservoir of potential sources for aquacultivation; fish often indicators of pollution. Regulation functions: stabilizing climate, hydrology of surrounding drylands (recharge of groundwater); biotic purification of organic matter and waste products; sink for siltation load of rivers; floodplain agriculture relies on regular supply of nutrients by floodwaters. The most important inland waters of West Africa are indicated in Fig. 9; the most extensive wetlands are shown on Maps 4 and 9. In Appendix 9 information on the water systems is summarized per country, with special emphasis on the occurrence of floodplain rivers. Savanna

Biotic production functions: wildlife, grasses, sometimes wood. Agricultural production functions: ranching, transhumance, wildlife utilisation, cultivation of The Environmentalist

subsistence crops (sorghum, millet, maize, cassava, legumes) and cash crops (cotton, peanut). Carrier functions: settlements, irrigation works, landscape recreation (game). Information functions: wildlife, gene-bank with respect to cultivated plants, forms adapted to extreme conditions (drought, temperature), endemic species. Regulation functions: contains life-forms of importance for agricultural production (predators and parasites, IPM); presence of vegetation shelters soil and water retention capacity, climatic stabilization. The greater part of the West African region consists of a savanna type vegetation (see Map 4). In Southeast Asia savanna vegetation is found on the Central Plains of Burma and in some smaller areas throughout the region (see Map 9).

From this description it is evident that all biomes represent a variety of production functions, either on land or in the water, which are often exploited by rural subsistence societies. At present the recreation potential of some areas receives much attention in particular with regard to the larger game animals of the savanna and waterfowl in wetland areas. Clearly information and information-reservoir functions are represented in all biomes. The importance of the regulation or stabilization functions of tropical lowland rainforests, for instance with regard to climatic stabilization and watershed protection are generally recognized (e.g., IUCN/UNEP/ WWF, 1980), but also other biomes perform comparable regulation functions. In the next chapter more detailed attention will be paid to ecosystems that are important

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Fig. 9. Main river systems of West'Africa (Welcomme, 19 7 2).

Riverine forest Biotic production functions: timber, fuelwood, source of organic matter for river system (fisheries), wildlife. Information functions: vegetation, wildlife, birds, invertebrates. Regulation functions: riverbank protection, shading prevents warming up and superfluous evaporation of river water; refuge of many animals during dry season, habitat of insect predators and parasites and birds; important as natural control agents in agricultural pest outbreaks. The riverine forest is an important element of the savanna. Vol. 4 (1984) Supplement No. 6

with respect to information and informationreservoir functions (areas of interest to nature conservation) and to some areas that are important with respect to production and regulation functions (wetlands). The production potential of many of these areas is high and in planning changes for agricultural developments one should be aware of potential interference with other function's performance.

5.3. Areas of Special Concern To achieve its objective of conservation of the living resources, the World Conservation Strategy 53

determined priority requirements: maintenance of ecological processes and life-support systems, preservation of genetic diversity and sustainable utilization of species and ecosystems. In the checklist on priority requirements in the World Conservation Strategy special emphasis is laid on the maintenance of the support systems for fisheries, the prevention of species extinction and the preservation of the habitats of desirable species and desirable ecosystems. Special attention is also paid to shared resources: species and ecosystems that fall under the jurisdiction of more than one country, such as international riverbasins, coastal systems and associated fisheries and migratory species. Accordingly, a selection can be made of areas of special concern with regard to the use of pesticides, namely protected areas, marine and freshwater systems, including wetlands, as well as a number of animal species which depend on these habitats. Protected areas

The natural environment and fauna in West Africa and Southeast Asia are relatively degraded and threatened. Especially in the humid tropical zone, the forests suffer most of all and many organizations and authorities have focussed their attention on this process (IUCN, 1976, 1978a, 1979a; IUCN/UNEP/WWF, 1980; Jacobs, 1981). In West Africa only a few of the remaining blocks of primary forest are under some form of legal protection and the actual protection depends on many other factors as well. The majority of the West African national parks and reserves are situated in the savanna zone, partly due to the attractiveness of the large wild savanna animals for tourists and partly to lack of claims on the ground by forestry exploitation or agriculture. The other ecological formations are poorly represented in protected areas. In Map 5 the national parks and equivalent reserves which meet the requirements on the UN list are indicated individually (IUCN, 1979a, 1980, 1981). Wetlands are marked separately. Other areas of interest for conservation, though not protected, are also indicated on the map. This category includes the range in which elephants have been reported (Douglas-Hamilton, 1979), assuming that this range represents a fairly undisturbed or uninhabited habitat. Appendix 10 gives the names of the areas on the UN list per country according to the numbers on Map 5. Burma, Thailand, Malaysia, Indonesia and the Philippines have a network of legally constituted or proposed conservation areas (IUCN, 1976, 1979b). Plans for the establishment and mainte54

nance of conservation areas were proposed for the remaining countries (IUCN, 1976; Mekong Secretariat, 1978). In Southeast Asia the lowland rainforest is the ecosystem least adequately represented in large protected areas because of the value of the timber it holds. This type of forest is richest of all in plant species and in those of actual or potential economic importance, and it is also the most valuable wildlife habitat. Map 10 gives the approximate situation of the existing and proposed protected areas in Southeast Asia. In view of the extensiveness of the region and the enormous number of protected areas no attempt was made to identify each area on this relatively large-scale map. For more information we refer to Appendix 11 and IUCN reports (1976, 1979b). Wetlands and watersystems

Wetlands, including swamps and marshes, are among the most productive of the world's ecosystems. The primary production (plant material) mainly occurs above the water table. The incorporation of this material into the food chain takes place in the water, where it is consumed by aquatic organisms, which are mainly decomposers (bacteria, fungi) and detritivores and include only a few herbivores and carnivores. In swamps a considerable part of the net primary production is transferred to other ecosystems (45 percent in a temperate salt marsh), for instance through tidal water movements or river floods (HowardWilliams, 1977). Thus a wetland supplies nutrients that may be utilized elsewhere. The type of biotic communities living in the different types of tropical waters vary largely depending on the type of water system they belong to. In a great lake the hydrology may be termed as stable, and the community of fish and other aquatic organisms may be classified as being in equilibrium, with relatively slowly maturing fish species, a low level of reproduction throughout the year and a certain degree of specialization among the species. Most rivers show seasonal fluctuations in the water level. An equatorial forest river has a high and low period twice a year, inducing seasonal variations in food availability, population numbers and peaks in productivity. The floodplain rivers in the less humid zones show large annual fluctuations of the water level. The floodplains of these rivers form an essential link in the productivity of the watersystem. The annual flooding and recession of the water causes a cycle of vegetation growth and death. As the savanna floods, the water is enriched in nutrients from the breakdown of organic matter, The Environmentalist

causing an explosive increase in the production and biomass of many aquatic organisms, both plants and animals. The geographical distribution of the major wetlands in West Africa and Southeast Asia are shown on Maps 5 and 9 and Fig. 9.

Fisheries Protein production through aquatic animals is in general highly efficient in the tropics, since cold-blooded animals grow quickly and efficiently in the warm, nutrient-rich waters. Therefore aquatic animals including fish, shrimps, crabs, shellfish and frogs are currently more important than wild land animals for the supply of protein, as has been shown clearly for the Mekong Basin (Mekong Secretariat, 1978). This is undoubtedly also true for the West African river basins. In many river systems fish breed during the time of rising water and migrate upstream and onto the floodplain to secure favourable conditions for the hatching, survival and growth of their larvae. Some fish species are so-called multiple spawners, who produce small batches at frequent intervals during the floods and show some form of parental care. Many other species in floodplain rivers are total spawners. They produce one batch per year at the start of the flooding and do not exhibit parental care. This high reproduction rate results in a high natural mortality and great seasonal wastage. On the other hand, species with the latter type of reproduction have a great potential for dispersal and many are long distance migrants. Hence, these are the species which may recover quickly after populations have been depleted locally by factors such as drought and pesticides. As most fish species on the floodplains mature in one or two years and life cycles are short, the turnover of populations is very fast and reproductive success is reflected very rapidly in the catches. As the water level falls, most fish return from the floodplain to the main channel and some species migrate downstream. During low water many fish crowd together in the restricted areas of the dry season refuges where food is scarce and predator pressure is high. Deoxygenation and desiccation of the pools also cause heavy mortality (Lowe-McConnel, 1975). The temperature of the water may vary considerably throughout the year. For example, in the Central Delta of the Niger the temperature of the water is almost 30 °C during the wet season (May to October) but drops suddenly to 20 °C in the dry season (December). Most fish stop feeding almost completely during low water in tropical systems (Daget, 1954). The rapid decomposition of organic matter as the water rises leads Vol. 4 (1984) Supplement No. 6

to deoxygenated conditions and an altered pH, and also the water of isolated dry season refuges often becomes deoxygenated and very warm. Yet most fish species in tropical rivers are well adapted to the widely fluctuating environment with a wide range of tolerance for temperature, pH, dissolved oxygen and other environmental parameters. In some species some special accessory breathing organs have evolved as well as the faculty of locomotion over wet land to survive frequent and abrupt environmental changes. Other habitats where populations are exterminated, are recolonized through seasonal migrations (Lowe-McConnel, 1975). The various species of fish exhibit group specific migration patterns. Some species move at a certain time of day, at a particular water level or only at one phase of the moon. Most river fishes move around a great deal and young fish and adults of the same species often live in different biotopes and form part of different communities during the wet season. Large numbers of fish fry appear at the edge of the newly flooded areas. As the water retires the fish population from a wide area becomes concentrated in the residual pools and depressions of the plains and spectacular catches can be made from them. In certain areas in West Africa trenches and dams are dug on the plains to retain water and fishes well into the dry season (e.g., in Nigeria, Ajayi, 1974). In Southeast Asia this form of fish cultivation is very much more developed and many farmers manage their own fish ponds. As many of the floodplains, for example in the Chao Phraya and the Mekong Basin, have been converted into agricultural land, the production of fish in ponds became more important. The tradition of fish cultivation in rice fields and irrigation canals was discussed previously in Section 4.1. In coastal areas aquaculture in estuaries and brackish water is also an old and well established tradition and is still expanding in certain areas, e.g., Malaysia (Ong, 1982). The ponds are stocked either naturally or artificially with fish seed caught in natural water or furnished by commercial fish seed farms. Fish species cultivated in West Africa are mainly Tilapia species and Heterotis niloticus (Vincke, 1976). In the Indo-Pacific region a large range of fish species is cultivated in fish ponds. A characteristic of most of these species is their ability to endure high water temperatures and low oxygen contents. Fish growth varies with food supply and fish ponds with these species can be very heavily fertilized, thus increasing yields tremendously. 55

In Indonesia the common carp represented 85 percent of the total fish production from paddy fields. Milkfish fanning is practiced and further developed along the coast in mangroves and swamp areas. In the Philippines milkfish ponds are very common. In Thailand coastal aquaculture developed recently, as many former salt farms are converted into brackish water fish ponds and shrimp and shellfish farms. In Malaysia Sepat Siam formed 70 percent of the production in rice fields on the west coast (Pillay, 1972; Vincke, 1976). Examples of some more species cultivated in Southeast Asia are given in Table 17. Sometimes several species with different diets are grown together in ponds or rice fields to exploit the available niches to the full. Shellfish and crustaceans may also be raised along with fish.

In m a n y cases t h e p r e s e n c e o f u n d i s t u r b e d n a t u r a l h a b i t a t s is indispensable f o r the m a i n t e n a n c e o f a q u a c u l t u r e , see also T a b l e 17. E s t i m a t i o n s o f the p r o d u c t i v i t y o f the various t r o p i c a l w a t e r s y s t e m s give an i n d i c a t i o n o f the i m p o r t a n c e o f an area for the p r o v i s i o n o f protein. T h e following e s t i m a t e s f o r the y e a r l y prod u c t i o n were e n c o u n t e r e d in the literature: river f l o o d p l a i n s 4 0 - 6 0 kg/ha, shallow lake ( L a k e C h a d ) 100 kg/ha, d e e p lakes 60 k g / h a , coastal lagoons 500 k g / h a ( W e l c o m m e , 1976, 1979) and fish p o n d s 100 k g / h a u n d e r l o w m a n a g e m e n t up to 1000 kg or m o r e p e r ha w h e n fed and fertilized (Vincke, 1976). A c c o r d i n g to F A O d a t a on fish f o o d c o n s u m p tion, in m a n y c o u n t r i e s o f b o t h West Africa a n d S o u t h e a s t Asia, s e a f o o d is r e p o r t e d to s u p p l y at

TABLE 17. Examples of species cultivated in Sou theast Asia (Pillay, 1972; Vincke, 1976; IUCN, 1979b) Species

Cultivation important in

Type of consumer, food taken

Stocking of ponds through

Cyprinus carpio

Indonesia Vietnam Malaysia Thailand

Omnivorous Young: zooplantkton, benthic organisms

Natural spawning in ponds

Philippines Indonesia Thailand Vietnam

Herbivorous: algae, benthic microscopic vegetable matter

Spawning in coastal waters, larvae collected along sea coast (peak: April-July)

Tilapia sp.

Indonesia Malaysia Thailand Philippines

Herbivorous: algae, vegetable matter

Reproduction in ponds

Triehogaster peetoralis

Malaysia Indonesia Thailand Kampuchea Vietnam

Plankton feeder and detritivorous: phyto- and zooplankton, decomposing plant material

Reproduction in ponds and paddy fields

Malaysia Vietnam Thailand

Omnivorous: insect larvae, worms, fish, bottom material Young: phyto-, zooplankton

Reproduction in ponds

(catfish) Mugil sp. (mullet)

Indonesia

Omnivorous: filamental algae, plants and animals

Larvae collected in coastal zone, reproduction in deeper sea (May Aug.)

Penaeus sp. Metapenaeus sp.

(prawns)

Philippines Thailand Indonesia Malaysia Vietnam Singapore

Macrobrachium rosenbergii

Thailand

(common carp)

Chanoschanos

(milkfish)

(Sepat Siam) T. trichopterus

Clarias batrachus

Larvae brought in with tidal water. Adults show offshore migrations (lunar periodicity) for spawning, larvae migrate inward. Collection in the Philippines, May-October

(giant fresh water prawn) Oysters

Philippines

Mussels

Thailand Philippines Indonesia

Cockles

Peninsular Malaysia

56

Filter-feeders 1 Filter-feeders

Seed collection from natural grounds

Filter-feeders The Environmentalist

least 15 percent of the total protein supply or over 30 percent of the total animal protein supply (IUCN/UNEP/WWF, 1980), notably in Senegal, Sierra Leone, Liberia, Ivory Coast, Ghana and Togo; and in Vietnam, Thailand, Malaysia, Indonesia and the Philippines. As was noted before, freshwater fisheries are as or more important in supplying protein in some of these countries. In Benin, Nigeria, Mali, Niger and Upper Volta, freshwater fisheries account for most or all of the total catch (see Appendix 8).

Fish-kill in the Mas river in Indonesia after misuse of pesticides for catchingfish. Photo: H. D. Rijksen. Water resource and development projects disrupt or modify hydrological cycles and thus often have deleterious effects on the aquatic environment and its living resources (Dill et al., 1975). The multiple use of rivers and lakes for agricultural and industrial development, associated with the building of dams and reservoirs brings about changes in the riverine habitat, fish food supply, spawning sites, nursery grounds etc., which will have differential effects on different fish species: some may benefit yet others may be harmed. Vol. 4 (1984) Supplement No. 6

Fish communities appear to undergo similar changes when subject to disturbing factors whether it be from pollution, modification of the environment or fishing pressure. These generally involve a progressive displacement of the community towards the smaller, faster growing but shorter lived species. The more highly appreciated food species are usually the larger, slower growing ones which disappear at an early stage after disturbance of the system. According to Welcomme and Henderson (1977), the control of the multiple users of the water needs to be strict, if the larger species are to be preserved. Attention should be paid to the preservation of refuges from which an overexploited or otherwise affected fish population may be restocked. The existence of traditional 'sacred lakes' where no fishing is allowed at all recognizes the importance of these refuges. Also the institution of a closed season for fisheries at the start of the floods may serve to protect the spawning stock to ensure optimal reproduction. The adoption of the principle of a 'closed season' should also be considered with regard to pesticides the use of which may endanger fish and fish food organisms. With respect to the vulnerability to pollutants, it is important to know the most vulnerable stages in the life cycle of fish, such as the reproductive phase and early life stages. Furthermore spawning sites should be respected. For instance in certain African river systems the spawning grounds are mainly on the edge of the floodplain at the beginning of the floods, thus representing a vulnerable part of the environment. Especially at the time of the dry season the main channel of the river which sometimes only consists of isolated stagnant pools forms another vulnerable locality. Fish populations are concentrated there while their condition is poor. Under these circumstances exposure to pesticides may cause severe losses. Birds The composition of the avifauna in tropical regions changes greatly during the year. For example in the West African savanna habitat, in addition to resident birds there are intra-African migrants that migrate southwards to woodland savanna during the dry season and then follow the rains up north into the Sahel zone. There are also intra-African migrants from south of the equator which appear seasonally. Moreover many species of intercontinental migrants of European and Asian origin winter in the same area. The migratory habit is a very conspicuous phenomenon in many bird species. A species may be termed a migrant when a large segment of the 57

population makes periodic movements to a nonbreeding area and returns. The migratory habit may be related to the geological past of the species as a response to climatic changes which necessitate periodic movement to avoid hostile environments (McClure, 1974). For instance insects are not easily available for food during the winter in Europe and Asia. Eurasian (or Palaearctic) migratory birds have their breeding area in Europe or Asia and their wintering quarter is the range in (sub-)tropical Africa or Asia where they stay during the northern winter. In the Palaearctic world four major so-called flyways can be distinguished: the Western Europe Flyway, where the birds fly from Western Europe southwest over North Africa, cross the Sahara or follow the West Atlantic coast into West and Central Africa; the Eastern European Flyway over Arabia and Ethiopia into East and Southern Africa; the Indo-Asian Flyway into the Indian Peninsula; and the Eastern Asia Flyway from East Siberia, Japan, Korea and China into Southeast Asia. Yet many species from East Asia and Siberia seem to favour a route southwest to India and even to East Africa and relatively few take the route to Indo-China, the Malesian Archipelago or even into Australia; this may be explained by past geological events and the colonizing history (McClure, 1974). Different species and even populations of the same species have their specific routes within a flyway as is illustrated in Fig. 10. In Southeast Asia the Philippines is the southern terminal for most of the migrants moving southeast along the East Asian flyway. Those that go further turn west along Palawan into Borneo and on into Indonesia. The closest approach to West Irian is along island chains (Sulawesi, Halmahera) but there is little evidence that land birds continue on this route (McClure, 1974). For waders the islands of East Indonesia (Wallacea) are reported to be not an important wintering ground (White, 1975). Malaysia lies at the south western extremity of the East Pacific Flyway. Migrants may winter on the continent or cross to Sumatra (McClure, 1974). Important wintering areas in Southeast Asia are the major river valleys of the Red River (Fisher, 1961), Mekong, Chao Phraya and Irrawaddy. In the Mekong River Basin about 500 bird species are resident and 160 are winter migrants (Mekong Secretariat, 1978). Of the 15 species of ducks known in Central Thailand 11 are migrants (e.g., pintail, teal, wigeon, garganey, shoveler, tufted duck, pochard). In the Philippines the Cagayan Plain, the Central Plain and Dalton Pass are important in relation to the Pacific 58

flyway. The island Mindanao receives less species but Palawan is again important on the route to Borneo. Of the 950 species and subspecies of Philippine birds, some 800 are residents (and many are endemic) and about 150 are migratory (Rabor, 1977). Of course all undisturbed natural areas and especially wetlands may serve as a wintering habitat (see Maps 9 and 10).

BO°

90°

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' " ROUTESIN EASTERNI ASIA. -Pacific . . . . . LAKE SOME

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Fig. 10. Some migration routes in Eastern Asia (McClure, 1974).

Compared to Asian bird migration relatively much information is available on bird migration in Africa (compiled by Moreau, 1972 and CurryLindahl, 1981). Whereas the birds migrating into Southeast Asia seem to encounter no other obstacles than water, those migrating from Europe to Africa also have to cross desert and arid areas on their way to their wintering range. The number of palearctic species wintering throughout West Africa is estimated by CurryLindahl (1981) to be at least 175. The majority of migratory birds, or 223 (sub)species, winters in the savanna zone, including the Sahel zone, the dry, moist and woodland savanna zone which crosses Africa from the Atlantic coast to eastern Sudan. For comparison, 35 migrant species are reported to winter in the ecological region of the lowland, transitional and montane rainforests along the west coast from Liberia eastwards, including Cameroon, Gabon and Zaire, and 54 The Environmentalist

species winter along the tropical coast of both the Atlantic and the Indian Ocean. In the Sahel zone the dry season begins at the end of September and lasts for eight or nine months. This means that upon arrival from Europe the vegetation is green and food supply optimal. However, during wintering, the situation deteriorates as the dry season proceeds. The Senegal Delta attracts spectacular gatherings of up to 200000 garganeys, 80000 pintails, one million ruffs, one million sandpipers, 200000 black-tailed godwits and many thousands of individuals of more than a dozen other European ducks and waders. Large numbers of European ducks and waders gather also in the inundation zone of the Niger, with over 100000 ducks, mostly garganey (Roux, 1976: one million ducks of which 500000 are garganey); and in Lake Chad, with up to 22 000 ducks, mostly shovelers and up to one million ruffs (Curry-Lindahl, 1981). The Niger River shows a 'delayed' floodregime during the local dry season from O c t o b e r November to April-May and many migratory aquatic birds congregate in December-May along the Niger River in Niger and on the inundated plains of the Logone-Chari River systems in Chad and Cameroon. The water bodies in the Sahel zone also attract large numbers of afrotropical waterbirds, but they are outnumbered by the migrants (Roux, 1980; Curry-Lindahl, 1981). In Map 5 these wetlands are indicated. At the onset of the rains organic production increases enormously: the vegetation develops, invertebrates are abundant and many other vertebrates (e.g., fish) reproduce. Some species seem to follow the rains and have more than one wintering quarter. That way they are assured of optimal food conditions in different seasons. During drought, the entire population of waterbirds from the Sahel may congregate in the Interior Delta of the Niger, birds coming from the east, Upper Volta, Chad as well as from Senegal. The birds may also go down south unusually far to the Gulf of Guinea. Many passerine migrants arrive in the Senegal Delta in September, where they stay for several weeks to refuel for the trip to southern West Africa (Liberia to Nigeria) to winter there. Some species do not arrive in the inundation zone of the Niger before December indicating that they had a stopover after their trans-continental flight in one or several other, hitherto unknown winter quarters. Thus, bird migration is a complex phenomenon of which many aspects are still unknown. The annual cycle of migratory movements between breeding and wintering areas is governed Vol. 4 (1984) Supplement No. 6

by the physiological state of the birds that changes throughout the season. In many long distance migrants moulting occurs prior to both spring and fall migrations. Some birds can also moult during migration or even stop to moult. Another physiological process preceding migration of Palaearctic migrants is the increase in body weight. In a period of 4 - 1 0 days before spring migration a short-distance migrant can increase in weight by more than 50 percent by storing fat, while long-distance migrants may take several weeks to fatten. Some species seem to intensify their feeding activities while fattening, whereas others are feeding as usual. In the more arid zones of the Sahel the dry period has lasted for over six months at that time and it seems to be a poor feeding area. Yet the birds seem to be able to put on enough weight quickly for spring migration. Moulting and fattening are two components of an annual cycle, synchronized by an internal and/ or external rhythm, including also gonadal development, migration and reproduction. This physiological cycle is perfectly synchronized with the environmental conditions on the breeding grounds, enabling the birds to arrive in time to start the reproductive process at once (CurryLindahl, 1981). Different populations of the same species have their own timetable of arrival and departure which has to be seen in relation to the intercontinental migration cycle as a whole. As a general rule long-distance migrants from the north arrive early in Africa and stay on late, whereas shortdistance migrants from southern Europe arrive late in their wintering quarters and leave again early in spring (Kwak and Stortelder, 1981). Consequently, the physiological process of moulting, fat accumulation and gonad development prior to migration is initiated at different times in the various species and subspecies and from February to May birds in one area may be found in various stages of this physiological cycle (Curry-Lindahl, 1981). Several Eurasian bird species show a great flexibility in their feeding habits by switching in Africa to food items which are unusual for them. Several migrants are opportunistic feeders, taking advantage of sudden abundances of food like locusts, swarming winged termites, ants and chironomids. This may lead to nomadic movements if the prey species are mobile. The birds may emerge and congregate as a result of rains and bush-fires, that cause increased activities of many arthropods. Some specialized insect feeders can periodically switch to fruits, berries and seeds, for example during an insect-poor dry season in the Sahel zone. 59

In recent years much concern has been expressed by nature conservation organizations about the hazards for birds, especially migratory birds, from pesticides. Many cases have been reported in which bird mortality has been attributed to pesticides. However, very little data is available on the use of pesticides in Africa, and on the effects on bird populations (Curry-Lindahl, 1981). Thiollay (1980) stated that he has seen thousands of storks destroyed after locust control, but other ornithologists remark that there is no proof that this was due to the pesticide used (dieldrin) (Morel, 1980; Roux, 1980; Curry-Lindahl, 1981). That the population of storks has crashed, however, might be due to lack of food (locusts). Locust control is reported to be detrimental also to certain birds of prey like Montagu's Harrier (Circus pygargus) (Thiollay, 1980), the Red-footed Falcon, some herons in Mali (e.g., the Cattle Egret, Ardeola ibis), shrikes (Laniidae), rollers (Coraciidae), bee-eaters (Meropidae) and incidentally small birds like the European Whitethroat (Sylvia communis) (Roux, 1980). Another point of concern is the control of granivorous birds with pesticides (parathion,

Birds killed after aerial insecticide (dieldrin) application against tsetse flies. Photo: H. H. de Iongh.

60

fenthion). It is claimed that control by night of the roosting sites of Quelea and Golden Sparrow colonies which are often located in or near aquatic habitats, has disastrous consequences for many other bird species such as cormorants, herons, egrets, swallows, sand martins (Riparia riparia), yellow wagtail (Motacilla /lava) and others that often sleep in great numbers in the same habitat. In addition ducks, waders, rails, gallinules and certain warblers use these habitats permanently. Moreover, all fish, amphibians, reptiles, birds and mammals killed by parathion attract storks, herons, kites, harriers and eagles, which could give rise to cases of secondary poisoning (Roux, 1980; Thiollay, 1980; Curry-Lindahl, 1981). Thiollay (1980) cites a Quelea control operation which was not effective as far as Quelea was concerned, but killed almost all other birds on the site. Ducks, the blacktailed godwit (Limosa lirnosa) and the ruff (Philomachus pugnax) are reported to cause crop destruction, especially in rice. When present at sowing time they will eat seeds and in new fields they may trample seedlings. Especially out-of-season crops on irrigated fields, providing food and water in an otherwise dry environment, are very attractive to the birds just prior to spring migration (Tr6ca, 1980). There are a number of more acceptable ways to prevent birds from damaging the crop, but some cases of intentional use of pesticides (spraying, coated seeds) were mentioned by Roux (1980). The control of disease vectors through pesticides (see Section 2.4) has caused considerable numbers of victims among birds as well as their prey species in the past, when methods were pretty rough and persistent compounds were used (Koeman et al., 1971, 1978). In tsetse control especially the smaller insectivorous birds in riverine forests turned out to be vulnerable. Opportunistic feeders exploit food sources of momentary and local abundance and are therefore important agents for the control of upsurges of insect pests (e.g., bollworms, borers in agriculture, grass hoppers, locusts). Through the increasing use of pesticides many of these sudden temporary food sources may become lost. The birds are liable to become affected indirecly through lack of food, as may also be the case for the white stork. Owing to greatly improved cattle-dipping administration there has been a decline in Nigeria of oxpeckers (Buphagus africanus) which subsist very largely upon cattle ectoparasites (Allan, 1975; Fry, 1975). The use of insecticides and herbicides in rice fields causes a decline of the aquatic fauna (insects, batrachians, fish, rodents) on which, for example, herons depend (Voisin,

The Environmentalist

1980). Newly sown grain seeds represent another temporary abundant source of food for ducks, ruffs and godwits (in case of rice) when they are present at sowing time. Therefore, seeds treated with some insecticide or fungicide may be detrimental for the birds. Comparable detailed information from Southeast Asia was not available. However, the IUCN report (1979b) on Thailand notes the relative lack of birds, both in number and species that are to be encountered in the inhabited areas of the country, including marshes, swamps and paddy fields. Comparable habitats in other parts of Southern Asia hold far greater bird fife and the use of chemicals in agriculture is suggested as the major cause, but this subject needs further investigation. In this section mainly migratory birds have been discussed. Yet it should be remarked that in Africa and also in Southeast Asia the majority of birds is sedentary, particularly in the equatorial lowland rainforests and montane rainforests with stable environmental conditions, but also in other biomes, despite environmental changes throughout the seasons. For all birds habitat loss seems to be the most important threat from which they may not be able to escape as virtually no other areas are available for retreat. Contamination of the habitat by pesticides could be considered as an aspect of habitat loss. It should be remembered that the principal habitats of Eurasian birds wintering in Africa are woodlands, grasslands, cultivated lands, marshes and coasts. Large areas of these lands are presently being developed (see Section 4.1). Yet, especially in the case of trans-continental migrants, it is difficult to an-

i

Month

2

3

4

alyse changes in polulation numbers and to prove cause-and-effect relationships since they cover long distances between distant areas and many factors may be operating at the same time. Bird migration is a very complex phenomenon that comprises many stages that may turn out to be vulnerable when exposed to pesticides. Pesticides may diminish the amount of food available for the restoration of their condition during step migration or before spring migration. Long-term effects on the reproductive success of certain bird populations have only been reported for DDT. The available toxicity data for many other pesticides do not suggest that this is a common phenomenon. The present evidence indicates that acute lethal effects and depletion of food organisms for birds are the most relevant effects which should be considered with regard to certain uses of pesticides. The impact for the total population of a catastrophe like a local extermination or sublethal effects will be different per species. Young (1968) states that direct mortality mostly affects long-lived slowly breeding species, whereas a reduced fertility has more effect on rapidly breeding short-lived species. The reproductive success in tropical birds is low, but adult survival is excellent, implying that the destruction of the adult population will take many years to recover (Fry, 1975). While judging the acceptability of these effects these longer-term effects have to be taken into consideration. Figure 11 provides an outline of the seasonal phenomena in birds in a West African habitat, for instance the Interior Niger Delta. Such diagrams show which phases of the bird's life-cycle

5

6

7

8

rains

9

i0

ii

12

(500 mm)

floods

fl.pl.recession

wet season

/

floodplain recession

Agricultural activities breeding Sedentary birds breeding Intra-african migrants I

Palaearctic migrants

non-breeding wintering wintering . . . . . . . . . . . . . . . . . . . . . . . moulting fattening refueling

Fig. 11. Life-cycle characteristics of West African birds in connection with seasonal land-use activities and climate.

Vol. 4 (1984) Supplement No. 6

61

coincide with certain agricultural activities and therefore require detailed attention. It is not the objective of the present report to provide a full coverage of vulnerabilities which may be distinguished in the environment with respect to pesticides. However, the approach used

62

in the valuation of the ecosystems as presented in this chapter suggests a procedure to be followed for other ecosystems and species in order to identify the ecological functions which may become affected and to assess the potential vulnerability to pesticides.

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