Land Use Problems in a Tropical Rain- Forest BY HENRI DOSSO, JEAN LOUIS GUILLAUMET AND MALCOLM HADLEY

The Tai Forest in the southwestern lvory Coast is the scene of rapid population growth and substantial development, which are quickly changing the last large tract of evergreen rain forest in West Africa. But the authors suggest it is also an area where research can still demonstrate that the needs of & a

are compatible with the needs of conservation.

120 AMBIO VOL 10 NO 2-3

i .*..o-- .. .. 1 Figure 1. Map of Ivory Coast and location of Tai Project area.

The southwestern part of the Ivory Coast contains the last extensive tract of dense evergreen rain forest remaining in West Africa-the Tai Forest (Figure 1). The lowland rain forest of Tai is situated between the Cavally and Sassandra rivers and includes tracts of swamp forest and riparian forest. The forest has a rich flora-over 150 endemic species have been identified-and considerable fauna, including populations of pigmy hip- popotamus and elephant.

Until the mid 1960s the region was largely uninhabited, with a small popula- tion which lived only along a few roads and on the coast. They made considerable use of the forest (hunting, fishing, food gathering) and grew rice on freshly cleared areas, which were th'en left fallow for a number of years. There were a few coffee and cocoa farms and limited forestry.

AMBIO, 1981

research station

F P pioneer front

In 1965, the Ivory Coast Government decided to develop this region of the country. An Authority for the Develop- ment of the Southwest Region (ARSO) was set up and massive investments were made in such projects as the San Pedro port and town, roads, agro-industrial complexes (rubber, oil palm and coconut plantations), the development of small towns, and peasant settlement areas. Other projects are still under way, such as the Sassandra hydroelectric dam, a paper- pulp production complex, a railway line, etc. More development is anticipated in the 1980s, but detailed plans have still to be drawn up.

In addition to this planned develop- ment, the region has attracted the spontaneous immigration of large num- bers of people from other parts of the Iv- ory Coast and neighboring countries. To the west of Soubré, these people have

established permanent farms on land formerly used by local shifting cultivators.

Like many other parts of the humid tropics the southwestern Ivory Coast is an area of rapid change. But it differs from many other regions in that it still contains extensive areas of untouched tropical forest. It is an area where scientific re- search can help shape and guide future economic development of this forest. To this end, the Ministry of Scientific Re- search set up the Tai project in 1973 (1,2).

The general objective of the Tai Forest Project is to improve the scientific basis for management of forest ecosystems. A number of interlinked studies have been developed among participating institu- tions and scientists from the Ivory Coast, France, Federal Republic of Germany, Italy, Netherlands and Switzerland to meet that objective. In this article two of the principal studies at Tai-one, now

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completed, on a front of pioneer settlers, the other, still underway, on the recon- stitution of vegetation following clearance and cultivation-will be described, to- gether with a discussion of tropical forest ecosystems as a source of airborne sulfur, and the role of the Tai Forest project for training purposes.

THE PIONEER FRONT The 1970s heralded an enormous growth in the population of the hitherto thinly populated Tai Forest region. Thus, in the Bakwé canton east of the Tai Forest, the population increased from 3484 in 1971, to 11 956 in 1975 and to over 15 O00 in 1977 (3). This massive increase can be attri- buted to the arrival of people from other parts of the Ivory Coast (particularly the Baoulé people) and from abroad, in their quest for land.

The Bakwé’s traditions of hospitality preclude them refusing access to the land to any immigrant. Often, they grant land without asking for money in return. Not surprisingly, a front of pioneers was established, and these settlers brought im- portant changes in agriculture and land use to the region.

Traditionally, the local Bakwé people practise swidden cultivation, based on slash-and-burn of ‘the forest, then cultiva- tion of one or two crop cycles, followed by abandonment and 15 or more years of fallow. The staple crop is non-irrigated rice; corn, manioc, taro and plantain bananas are also grown. Food crops are supplemented by hunting and trapping of small mammals, and by gathering cola nuts, wild tubers, medicinal plants, caterpillars and other products of the forest.

In contrast, the immigrants’ economy includes cash crops, particularly coffee and cocoa. Their use of the land is inten- sive and relatively tightly organized. After forest clearance, food crops (eg yam) and plantation crops follow each other in reg- ular succession. There is no fallow period.

At first, the indigenous people adopted a favorable attitude towards the im- migrants. The newcomers represented a source of labor for working the land. They served to keep predatory animals at a dis- tance and were of direct economic benefit to the local populations. Gradually, how- ever, the indigenous people began to lose control of the immigrants, as the latter began to arrive in ever increasing numbers and to dominate the local economy. The local people came to regard immigration as a form of dispossession. “Bakwé country has become Baoulé”, said one elder when expressing his worries about the Bakwé’s future.’

In this light, a number of steps have been taken by the authorities to try to resolve or avoid conflict-for example by giving the Bakwé powers to control new arrivals by means of a register, in which

all new applicants for land are recorded; by building dispensaries and schools in Bakwé villages, and not in the outsiders’ settlements, even though the latter are sometimes ten times larger; and by con- centrating the Bakwé villages. In addition, all discussions regarding the region’s fu- ture are held in the Bakwé villages, the immigrants settlements being requested to send their representatives to such discus- sions.

Research within the Tai Forest project documented the factors which enabled the pioneer front to establish itself and high- lighted the conflicts between a new land use strategy and a traditional one. At the end of the study, recommendations were made to the government concerning the possible consequences of, and reactions to, the expansion or establishment of new fronts of pioneer farmers.

State action in the region is represented by the Authority for the Development of the Southwest (ARSO), which is directly attached to the Presidency of the Re- public. A development strategy has been elaborated (4) which has three phases: im- mediate exploition of the forest in order to make the port of San Pedro profitable; creation of major agro-industrial projects to provide employment and trade after the timber harvest; and setting up viable in- dustries to ensure this region’s economic development.

The different categories of users are allocated land according to a land use map, which is periodically revised. As time passes, the map is becoming increas- ingly detailed, to include, for example, medium-sized plantations. The land is di- vided among the native cultivators, im- migrant planters, village plantations at- tached to agroindustrial blocks, and var- ious types of family agriculture (rice, cocoa, coffee, e tc) , all of which occupy the areas lying between the large agro-in- dustrial complexes of oil palm, rubber and coconut oil. This aspect of future land use is the most difficult to plan, and as such has been rather neglected in the past in plans for resource management.

THE FOREST AND ITS RECONSTITUTION The natural forest regenerates itself in gaps left by individual fallen trees. Ani- mals are important in disseminating the seeds of canopy trees, and in maintaining the floristic diversity of the forest (5). Out of 71 species of trees in the Tai Forest whose seed dispersal is known, 21 (30 per- cent) are dispersed by elephants. More- over, germination seems to be more rapid and vigorous for those seeds that have passed through the gut of the elephant.

The same process does not work in a denuded one to two hectare area of abandoned field. The primary forest trees are relatively slow growing. Their seeds are not plentiful and they require shade

and moisture for germination. These trees are not able to re-establish themselves on land that has been abandoned following clearance and cultivation. Because these primary tree species cannot compete in- itially with sun-loving, pioneer species, the forest depends on Macaranga and similar species for its regeneration and re- constitution.

Thus, considerable attention has been given at Tai to morpho-structural and floristic analysis of the forest and its suc- cessional stages (6) (Figure 2).

The first phase is dominated by graminaceous plants, with rice as the cultivated crop. The second stage in- cludes tall, non-graminiform herbs and semi-woody plants, and such crops as cassava, banana and pepper. The third phase consists of shrubs and small trees, often dominated by single species such as Macaranga hiirifolia. This gives rise to a fourth phase, the pre-forest stage. This stage has the structural characteristics of the climax forest, though its floristic com- position is different.

In the Tai forest, Macaranga hurifolia plays a key role in the reconstitution of the forest. In other parts of the Ivory Coast, species such as Trema guinesis and Musanga cecropioides fulfil a similar function (7). These plants tend to be sun- loving trees with a short life span which appear in the forest, following more or less extensive disturbance (8).

These species share a number of im- portant characteristics. They have a low life expectancy, generally less than 20 years. Their growth is very rapid, with maximum height usually attained in 6-7 years. Flowering and fruiting are preco- cious and prolific.. The trees are sexually mature at 2-3 years. Seeds are small and are produced in large numbers. Seeds re- main viable for several years, but seedling mortality is high. Macaranga seeds are often parasitized by a Chalcidian Hymenoptera belonging to the genus Eurytoma. The larva of this insect under- goes all its metamorphosis inside the seed. Of 100 seeds taken from a single Macaranga at Tai, 65 were empty and pierced, 30 were parasitized by larvae in various stages of development and only 5 were intact (9).

Macaranga has a characteristic root system. Full root potential is very quickly achieved through an intensive and rapid occupation of the superficial soil layers. The primary forest trees require much more time to achieve the same result.

After about 3 years, root grafts appear between individual Macaranga plants. Radio-active tracers (Paz) have been used to evaluate the function of these root grafts (10). These experiments have shown that some individual trees “feed off’ and drain the root system of their neighbors, and eventually take over the living part of the root system after the death of the neighbors. Root grafts, thus

122 AMBIO VOL 10 NO 2-3

Figure 2. Phases in the reconstitution of vegeta- tion after cessation of cultivation. I. Stage with Gramineae dominant. Crop

grown: rice. II. Stage of tall non-graminiform and sub-

ligneous herbs. Crops grown: cassava, banana, okra, pep- per, etc. Shrub stage dominated by one or more (2- 4) species, varying according to edapho- climatic conditions and farming methods. Pie-forest stage. Establishment of forest structurally similar to climax forest, but with different floristic composition.

111.

IV.

1 2 7

?

II__ -

Testing out traditional logging techniques-cutting, burning, and cultivating (better known as the slash and burn technique).

years 30

serve to increase the rhizosphere of some individuals, while accentuating the degen- eration of others.

Macaraizga is not able to regenerate un- der its own cover. Populations begin to decline between 6 to 13 years and are gradually replaced by “forest” species.

Figure 3 (after Alexandre et a l , 11) sum- marizes some quantitative aspects of the Macaranga stage of forest regeneration. After about 13 years, the basal area already totals about 50 percent of that in the natural forest (curve V). There are fewer trees of small circumference (1 1-40 cm) than in preceeding years; some species have already grown out of this range, and others (in particular Macaraiiga hurifolia) have been gradually replaced by “forest tree” species. At the end of the Macaranga stage, there is a reduction in the basal area of smaller diameter trees. Several years after the end of the Macaranga stage (ie after about 18 years), the basal area (curve VII) is about that found in the “natural” forest. After 18 years, there is a marked increase in the number of individuals and of species, with a relatively high proportion of “forest” species (curves I, II, III and IV).

These botanical studies on forest recon- stitution at Tai have been closely linked with work on changes in other ecosystem characteristics, such as soil status and animal populations. The first results obtained by the pedologists show that forest clearance followed by burning re- sults in a considerable reduction in the overall activity of the soil. However, the soil rapidly regains’ its former levels of organic matter content, and other princi- pal characteristics. This restoration of soil fertility occurs before the end of the shrub and small tree phase. The significance of these results is that it should be possible to shorten present fallow periods, once the difficulties involved in clearing dense vegetation, and in ensuring against out- breaks of certain animal pests and para- sites have been surmounted.

Changes in run off and erosion rates under different treatments have been fol- lowed in six plots (each of 250 m2, three

AMBIO, 1981 123

Figuire 3. Changes in floristic and structural char,acteristics during reconstitution of the forest (after Alexandre et a/, Reference 11 1. I. Total number of individuals of woody

plants. II. Total number of species of woody plants. 111. Number of forest tree individuals. IV. Number of forest tree species. V. Total basal area (m2/ha) VI. Total basal area of primary forest. VII. Basal area of trees of circumference 11-40

cm. (See basal area of such trees in primary forest, Vlll).

under forest, t--ree under crops) and in drainage basins of area 7.3 ha (forest) and 3.3 ha (crops) (12). The average rainfall at Tai is about 1900 "/year, and the annual run-off rates averaged 4-5 percent under forest, and 15-20 percent under crops. Perhaps surprisingly, similar low rates of erosion were recorded under traditional agriculture and within the forest control (average 0.25 g/l, with peaks of about 1.25 g/l).

The vegetation cover in the cultivated basin (rice, young forest regrowth) pro- vided a similar protection to that of the maflure forest, the overall erosion rates being in the order of 100-250 kg/ha/year. Infiltration rates following simulated rainfall experiments appear to be affected more by soil type than by vegetation cover. In the event that new agricultural techniques involving working of the soil are introduced widely at Tai, then the lower lying areas of drainage basins would appear to be particularly vulnerable to in- creased run-off.

TROPICAL FOREST AS A NATURAL SOlURCE OF AIRBORNE SULFUR Pollution is a phenomenon usually as- sociated with industry and other human activities, but natural areas may also be sources of some substances often thought of as polhtants. Work in the Ivory Coast has, shown that the tropical forest may be a significant natural source of airborne sulfur.

Thus, about 15 km west of Abidjan at Adiopodoumé, sulfur dioxide concentra- tions averaged 10 pg/m3, with maximum levels of 30 pg/m3 (13). The high annual deposition rate of sulphates (2050 mg/m2)

MACARANGA HURlFOLlA I

----------- VI T 35

2 6 NUMBER OF YEARS

is comparable to tha observed in rural areas of western Europe and attributed mostly to anthropogenic sources. In the area west of Abidjan, the contribution of artificial sources of SOz can be safely dis- counted, in view of the direction of pre- vailing winds. Oceanic sources are also negligible.

Data also indicate that hydrogen sulfide emissions from soils are on average higher from the soils of humid equatorial forests in the Ivory Coast (0.012 to 0.3 g/m2/h) than from the soils of agricultural land in France (0.002 to 0.03 g/m2/h) (14). Ground level concentrations of hydrogen sulfide also tend to be much higher in the forests of the Ivory Coast (100-6000 ng/m3) than in agricultural areas in France (50-300 mg/ m3) as is shown in Table 1.

The clue to these high levels of sulfur seems to lie in the decomposition of or- ganic material in the tropical forest ecosystems, particularly as a product of anaerobic decomposition processes. Further work is now underway at Tai and other sites in the Ivory Coast, to analyze gas emissions from the soil and to provide in situ measures of the intensity of gas outputs. It is hoped that this work will result in a complete description of the natural cycle of sulfur in intertropical re- gions. Data from such work should also help to clarify the role of tropical. forest ecosystems in the phenomenon of acid rain in these regions (15).

RESEARCH FOR TRAINING AND TRAINING FOR RESEARCH The Tai project is particularly important for the development of the Ivory Coast's scientific policy (1) since it serves as a

30

m c 20 -. f

10

focal point for bringing together the con- cerns of natural as well as social sciences, basic as well as applied research, and re- search as well as development. It is also important for its role in the training of Ivory Coast research workers.

The Ivory Coast still lacks trained peo- ple in a number of technical fields. Thus, cooperative links have been developed with other countries, in order to fill gaps in the research program and to help train local specialists. The Ivory Coast has made a substantial investment in field in- stallations within the Tai project so stu- dents can receive field training within the ecological and socio-economic context of their own country and region.

The Tai Forest Project is also a site for training people from other countries of West and Central Africa. Many countries of this region lack suitable facilities and programs for field training on tropical ecology, and can therefore take advantage of the opportunities provided by the Tai project. A four-week regional training course on the ecology of humid tropical forest ecosystems was held at Tai in January-February 1980. Supported by UNESCO and UNEP, this course brought together some 25 participants from 9 francophone countries ((16). To our knowl- edge, this is the first occasion that a regional training program of this type has been held within the tropical forest itself in West and Central Africa. Moreover, almost all of the participants met for the first time at Tai. The training course thus served to develop personal contacts be- tween young specialists from countries of a region where mechanisms for interac- tion are largely lacking.

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CONCLUSION The Tai Forest Project is focused on an area where rapid development and popu- lation inflow are placing increasing pres- sure on a virtually untouched forest. Yet there is still time for research to precede or to match the increasing human activity. There is still time for research workers to increase their knowledge of the forest and to make recommendations for the long- term, predictable management of the natural resources of the area.

The Tai Forest Project, therefore, pro- vides a good opportunity to demonstrate that the needs of development are com- patible with the needs of conservation and that, in fact, the aims of development are best served by the planned, rational use of the resources of the tropical rain forest ecosystem.

The project provides a firm logistic basis for cooperative work on tropical forest ecosystems. It has benefited from a substantial national commitment and from the involvement of scientists and institu- tions from several countries. We hope that this commitment and involvement will be continued and strengthened, so that the project can reach its full potential for contributing to the science of tropical ecology and to the development of the scientific capacity of the Ivory Coast and other countries of the region.

References and notes

1. See articles by J Lorougnon Guedé, J L Guil- laumet and N’Guessan Kanga. Nature and Re- souyes , 12 (No. 2), pp 2-8 (1976).

2. H Dosso, J L Guillaumet, in Transactions of the International MABlIUFRO Workshop on Tropical Rainforest Ecosystems. E F Brunig, Ed. (Special Report No. 1, Chair of World Forestry, Hamburg Reinbek 1977) pp 95-103.

3. J F Rickard, P Léna, F Martinet, A Schwartz. Le dynamisme pionnier dans le Sud-Ouest Ivoirien, ses effets sur le milieu forestier. (Région de Soubré). Proje? Tai, 1, (1977). Synthesis of this study available as Report SS-77/WSll5, No. 4 in the,series “Human settlements and socio-cultural environment” (Unesco, Paris, October 1977).

4. G Sautter, A Mondjannagni, in Management of natural resources in Africa: traditional strategies and modern decision-making (Unesco, Paris, MAB Technical Notes 9, 1978), pp 57-81.

5. D Y Alexandre, Terre et Vie, 32, pp 47-72 (1978) 6. D Y Alexandre, J L Guillaumet, F Kahn, C de

Namur, R Moreau. Observations sur les premiers stades de la reconstitution de la forêt dense humide (Sud-Ouest de la Côte d‘Ivoire). Special volume. Cahiers ORSTOM. sér. Biol. 8 (No. 31, pp 189-270 (1978). For further insights and refer- ences on tropical forest succession, see such re- views as: H S Horn, Annual Review of Ecology and Systematics, 5 , pp 25-37 (1974); Tropical forest ecosystems. A state of knowledge report prepared by Unesco/UNEPlFAO (Unesco, Paris, Natural Resources Series 14, 1979), pp 216-232; F A Bazzaz, S T A Pickett, Annual Review of Ecology and Systematics, 1 1 , pp 287-310 (1980).

7. Analogous populations of the same or different species have been reported in Nigeria (Ross 1964), in Zaire (Lebrun and Gilbert 1954), in Ghana (Taylor 1960) and in Gabon, Cameroon and Congo (Aubreville 1947). Similar populations are found in Asia (Richards 1957) and in Latin America (Lescure 1978).

8. Collectively, these plants have been referred to in a varietv of wavs. includine “biological nomads’’ (Van Stkenis li56), “weeltrees” :Corner 1952), “scar species”, after the way they seem to heal younds in the forest (Mangenot 19551, and

pioneer species”, appearing in open spaces be- fore other species (Whitmore 1975).

9. F Kahn, C de Namur. Cahiers ORSTOM, série Biologique 8 (No. 3), pp 255-259 (1978).

10. F Kahn, Cahiers ORSTOM, série Biologique 8 (3), pp 239-254 (1978).

11. D Y Alexandre, J L Guillaumet, F Kahn, C de Namur. Cahiers ORSTOM, série Biologique 8

12. J Collinet, Compte-rendu de deux Campagnes de simulation de pluies sur le bassin cultivé de la station écologique de Tai. Projet Tai (1979).

(NO. 3), pp 267-270 (1978).

Table 1. Hydrogen sulfide in air at ground level in the Ivory Coast and at ground level and at altitude in France (Reference 13)

LOCATION SITE CHARACTERISTICS AIR CONCENTRATIONS (ng/ms) (Number of measures) Average (Min.-Max.)

IVORY COAST Forest of Tai

Forest of Banco

Forest of Dabou

Anaerobic site (4) 6082 (5810-9700) Aerobic site (1 1) 656 (1 60-2888) Anaerobic site (1) 5800 -

- II) 4020 - Aerobic site (60) 800 (200-1200)

Lagoon of Ebrie Center of Lagdo’n (4) 103 (20-150) Lagoon shore (4) 515 (380-820)

Savanna of Lamto Aerobic site (4) 465 (450-500) San Pedro Anaerobic site (1) 1400 -

FRANCE City of Toulouse Urban area (39)

Residential area Residential area

Val de Loire Rural area (5) Landes Rural area (IO)

Pine forest (3) Languedoc (coastal Continental air (24) area) Marine air (24) Pic du Midi Free atmosphere (IO) (3000 m altitude) Continental (21)

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94 41 110 80 91 63 70 335 7

106 -

(0-174) (20-71)

(39-173) (33-227) (55-73)

(52-21 6)

(43-1 15)

(2-1 8) (1 1-357)

(71-884)

13. R Delmas, J Baudet, J Servant, Tellus, 30, pp 158-168 (1978).

14. R Delmas, J Éaudet, J Servant, Y Baziard. Emis- sions and concentrations of hydrogen sulfide in the air of the tropical forest of the Ivory Coast and of temperate regions of France. Paper presented to the Fourth International Conference of the Commission on Atmospheric Chemistry and Global Pollution (12-19 August 1979. University of Colorado, Boulder).

15. Two forthcoming SCOPE publications are rele- vant to the general problems of acid rain and sulfur cycling: Some perspectives on major biogeo- chemical cycles (SCOPE 17); The global sulfur cycle (SCOPE 20). (Wiley, Chichester, New York, Brisbane, Toronto, in press).

16. Trainees included young scientists from Benin, Burundi, Central African Republic, Congo, Ga- bon, Ivory Coast, Rwanda, Togo, Zaire.

Henri Dosso was one of the first re- search workers to take part in the Tai Project, as a specialist in forest ro- dents. He is scientific secretary of the Ivory Coast MAB National Commit- tee, and has, since 1979, been Di- rector of the Ivory Coast University Institute of Tropical Ecology. In his present capacity, he is responsible for the general supervision of the Tai Project. His address: Institut Uni- versitaire d‘Ecologie Tropicale, B.P. 8109, Abidjan, Ivory Coast.

Jean-Louis Guillaumet, a botanist, is research director with the French Of- fice for Overseas Scientific and Tech- nical Research (ORSTOM). He work- ed mainly in the Ivory Coast and Madagascar before being appointed by the Ivory Coast Minister of Sci- entific Research to take charge of the scientific coordination of the Tai Pro- ject and to direct the University Insti- tute of Tropical Ecology, which he did from 1975 to 1979. His address: Instituto Nacional de Pesquisas da Amazonia, Estrada do Aleixo, 1756. 69000 Manaus (AM). Brazil.

Malcolm Hadley is Program Specialist in the MAB Secretariat in UNESCO, where one of his tasks is to promote integrated pilot projects linked to land development in the humid and sub-humid tropics. A zoologist by training, he received his Ph.D. on the population dynamics of dipteran flies from the University of Durham, United Kingdom, in 1967. Prior to joining UNESCO in 1972, he worked for some five years with the International Biological Program (IBP), where he had a special interest in terrestrial productivity and the ecology of tropical savannas. His address: Division of Ecological Sci- ences, Unesco, 7, place de Fontenoy, 75700 Paris, France.

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