The isolated effects of tsetse control on natural resources after successful implementation of control measures are hardly understood and controversially discussed. The natural resources are never affected by tsetse control alone but by a wide range of other factors occurring parallel thereto. These include socio-economic, sociological and demographic processes which are inter-dependent and act in combination on the landscape. Opinions as to the actual influence of tsetse control measures on the natural resources range from the view that the “wilderness” can only be protected by refraining from all control measures to the claim that the consumption and degradation of the natural resources within the tsetse belt continues anyway without any tsetse control measures (ref. Swynnerton 1936, Grzimek & Grzimek 1959, Ford 1971, Ormerod 1976, Jordan 1986, Nagel 1988, 1991). This problem was, for example, examined by Jordan (1986, 1992) founded on a partly different formulation. Based to a greater extent on general considerations and experience rather than on detailed studies, the view today tends mostly to the assumption that the “Grenzwildnisse” have been reclaimed, even if with delay due to the presence of the tsetse fly, and that, on the other hand, tsetse control measures facilitate possible adverse effects on natural resources.
Apart from the effects, such as on the economy, which are not directly relevant to the question being posed, possible primary effects of tsetse control, in part intentional, can be defined as being:
Possible secondary effects of tsetse control measures could, for example, be:
Only a few of these potential effects can be discussed herebelow. Reference to a concrete example is very important, in order to clearly demonstrate the variety of inter-dependences. As part of a GTZ project, the possible effects of tsetse control measures were studied from 1991 to 1993 in the North and Central Côte d'Ivoire. An excerpt of some of the results is presented below.
2. DIRECT SIDE EFFECTS OF TSETSE CONTROL MEASURES ON ECOSYSTEMS
With the exception of a few earlier ground-spraying operations, widespread control of the tsetse fly as a part of the control of animal trypanosomosis (nomenclature after Kassai et al. 1988), is, nowadays, in the Côte d'Ivoire, exclusively conducted by the use of stationary targets. The ecological side-effects (ecotoxicological side-effects included) of the residual and aerosol applications of the most important insecticides are today as well-known as those of the unbaited or odour-baited traps and targets (cf. Everts & Koeman 1987, Müller 1989, Semg 1987, 1993 a,b). The necessity of an environmental monitoring programme accompanying the control measures is nowadays beyond dispute. In the meantime, instructions on the execution of such monitoring programmes are available (SEMG 1993b, cf. FAO 1975). While, in the case of residual applications considerable negative effects on non-target organisms must partly be expected, the effects of aerosol applications are usually easily identifiable but tolerable. The implementation of stationary targets currently comprises the most environmentally-sound control method. To date, no or negligible side effects of this method have been proven and are only to be expected in exceptional cases as a result of the consequent cultivation of an area.
3. PRESENT STATE OF SELECTED NATURAL RESOURCES IN THE STUDY AREA
One possibility of analysing the effects of tsetse control is the comparison of the land-use dynamics in comparable areas, one with and one without tsetse control, but otherwise with almost identical conditions. As tsetse measures towards control of animal trypanosomosis are usually conducted over widespread areas, it is very difficult to find two such areas. In the Côte d'Ivoire, one area with a long history of tsetse control and two areas, in which tsetse control has only just begun, were, therefore, selected to conduct studies covering actual vegetation and land-use as well as vegetation and land-use dynamics.
The studies were made on the basis of aerial photos and field studies, whereby part-areas representative of the whole area were intensively examined (cf. Erdelen et al. 1991, 1992a, b, c, 1993).
3.1 Current Situation in the Tsetse Control Area (Région Korhogo)
The extensively-utilised grazing resources in the area examined, North of Korhogo, practically cover the whole area. Nevertheless, grazing degradation (over-grazing, formation of vegetation of compacted soil) could only be detected along the main routes of transhumance, as well as, occasionally, in the area of sedentary cattle farming (e.g. also in the bordering areas of settlements). Places more or less free of human impact also display a greatly increased proportion of annual grasses, including grasses with a low fodder value (e.g. Ctenium newtonii) and a greatly decreased proportion of overground biomass, compared to the Central Côte d'Ivoire. A clear indicator of excessive grazing is, in contrast, among others, the regionally untypical increase in the proportion of annual grasses and herbs. The grazing degradation is characterised by the establishment of annual secondary vegetation with typical indicator species, such as Tribulus terrestris (Zygophyllaceae), Indigofera congesta, Indigofera geminata (Papilionaceae) or Waltheria indica (Sterculiaceae).
TABLE 1 Comparison of the Three Areas Examined in the Côte d'Ivoire
|Région Korhogo||Région Tortiya||Région Bouaké|
|Vegetation||Sudanian Woodland||Sudanian Woodland/ Guinea Savanna/ Forest Transition||Guinea Savanna/ Forest Transition|
|Tsetse control||Since 1978||Since 1992||Since end of 1990|
In the whole Northern study area extensive, dense low-growing stands of Detarium microcarpum and Isoberlinia doka point to earlier agricultural use. Further indicator species of such former agricultural utilisation are to be found in the loose, but regular distribution of Vitellaria paradoxa and Parkia biglobosa, which, as shade-providers and fruit-trees, were usually not felled upon field cultivation, but were sometimes even deliberately planted. As in other African countries, cotton plantations are constantly taking up increasingly larger areas. In highly degradated, poor-quality fallow land, the Guiera senegalensis bush can often be found: a flora invading the South from the Sudan zone.
The woodland areas also displayed pastural degradation as a result of excessive grazing. The Forêt Classée de Badénou (forêt claire) is subject exclusively and to an above-average extent, to grazing. Peul are the semi-sedentary users. In October 1991 practically no areas without damage caused by grazing in the whole woodland could be located. This is obviously a recent development, as the flora displayed no essential differences to comparable areas examined. However, short-term changes in the fire pattern will result with an increase in bush formation and thus a long-term reduction in the grazing potential.
3.2 Current Situation of the Vegetation in the Central Côte d'Ivoire (Bouaké Area, where tsetse control has just begun)
In the area under particular examination on the River Nzi, extensive grazing utilisation still plays a subordinate role as an influencing factor, despite potentially good grazing land (cf. IFG 1982). In recent years there has been an increase in cattle farms, which are usually intensively used. On these extensive, fenced-in natural pastures there is already evidence after only a few years of use, and with a stock density in proportion to the total farming area, of severe degradation of the savanna, in particular in the vicinity of cattle shelters, trample-paths or watering areas. In extreme cases the perennial grass communities are replaced mainly by annual trample grass communities (e.g. the grasses Brachiaria stigmatisata, Panicum pansum, Eragrostis ciliaris), in which, in places, even sudano-sahelian flora such as Zornia glochidiata (Papilionaceae) and Tribulus terrestris (Zygophyllaceae) take hold. Once the grass surface has been grazed thin, the primarly neotropical Chromolaena odorata (formerly: Eupatorium odoratum) (Asteraceae) can be found in the form of extensive undergrowth in some places. Due to its content of aromatic Pyrrolizidin alkaloids, it is avoided by cattle. Incidentally: the stinking grasshopper, Zonocerus variegatus, a cassava, coffee and cotton pest, for example, protects itself from its enemies by deliberately consuming this plant substance. Thus, the damage potential of the stinking grasshopper in West Africa is increased by the spread of C. odorata. A further consequence of the excessive grazing in these areas is the increasing formation of bushes. However, in most of the places examined, where grazing was not excessive, no serious changes in flora structure could yet be determined. A reduction in the herb biomass was typical. Thus, within the grazing area of a cattle farm the overground herb biomass amounted to 7.9 t/ha (dry weight), whereas immediately outside in the non-pasture area it reached 9.5 t/ha. Even moderate grazing at this early stage results in an increase in germination of woody plants with consequent alteration in the fire pattern.
4. HISTORY OF LANDSCAPE PATTERNS
In the area with tsetse control since the end of the seventies (North of Korhogo) the area of settlement more than doubled in the twenty years prior to tsetse control and has trebled in the last twenty years. The agricultural areas grew in the pre-control period by almost three-times the size, however in the last twenty years by only 20% (figure 1).
As early as 1974 – 1978 an evaluation of the land showed an almost total cultivation (area under cultivation and fallow land) of the area direct South and East of Korhogo (IFG 1982). The areas covered by gallery forest were reduced during the periods shown in figure 1 by 42%, respectively 27%, and a corresponding reduction of dense woodland amounted to 47%, respectively 24%. The great reduction of the natural resources “gallery forest” and “dense woodland” had thus already commenced long before introduction of the tsetse control measures and slowed down after implementation thereof. Parallel hereto, the phase of main expansion of cultivated areas took place prior to commencement of tsetse control measures.
FIGURE 1 Dynamics of Land-Use and Landscape Structure in the Study Area of the Korhogo Region with Tsetse Control since 1978 (based on aerial photos and field studies, size of the area examined: approx. 100–150km2)
The development of the landscape changes in the area around Tortiya (tsetse control measures since 1992) was, in principle, similar (figure 2). Here, too, the gallery forest area was reduced by 34% between the mid-60's and the end of the 70's, however, since then, to date, by a further 56%. The reason in this area is not so much the agricultural cultivation of these resources as in the area around Korhogo, but is related more to the diamond mining. The dense woodland was reduced during both periods by 52%, res-pectively 36%. Parallel hereto, the cultivated area increased by more than 11 times, respectively by almost three times as much.
During these 40 years there has been, not only in Korhogo city, but also in the rural areas under study, a considerable increase in population, with now approx. 13 inhabitants per km2 in the latter. At the same time, a far-reaching change in structure has taken place within the agricultural sector. The main ethnic group of the Sénoufo was, originally, a subsistence-orientated agricultural community, but they have - similarly to neighbouring ethnic groups of the sub-Sudan zone - converted their farms, for the most part, into more intensively-farmed cotton plantations. An essential characteristic is the greater stage of mechanisation on the farms, reached through the introduction of draught oxen. In addition to the breeding of draught animals, the usually extensive cattle breeding represents the production sector gaining most in importance. The ethnic group of the Peul comprises, primarily, large-scale pasturalisers, who, as in almost the whole sub-Sudan zone, are increasingly operating as semi-sedentary agro-pasturalisers.
Since 1960 an increase in animal-breeding has been registered in the Northern Côte d'Ivoire, developing at different places. Up to the 70's this was almost exclusively sedentary cattle stocks, which grew parallel to the population. At this time the population drift from the North increased, parallel to an increase in sedentary cattle, with a rate of growth well above that which would be expected from the growth of the population. Up to the mid-80's this caused more serious conflicts between the two main ethnic groups. Since then the increase in cattle stock has re-adjusted to the general population growth in the rural area (Kientz 1991).
This change within the two ethnic groups from complementary to competitive production already results today in increased com-petition for the natural resources agriculture land and pasture-areas. Typical for this area is, therefore, a shortage of pastoral resources as a result of the conversion from pasture to agriculture land, at the same time, however, also a shortage of areas available for plant production.
Independently of the existence of endemic diseases such as onchocercosis and trypanosomosis, settlements always developed in areas with high-yield land, good pasture land and sufficient water supplies during the dry season. Outside of these well-endowed areas, extensive woodlands usually remained intact. However, there are indications that, in the meantime, as a result of increased demand, woodland previously not used, is being integrated into the pasture areas (see above). It is possible that this development is being facilitated by tsetse control measures.
The decisive change and the pressure on the natural resources started prior to commencement of tsetse control. The current further increase in the total cattle stock can most probably also be attributed to the tsetse control measures, however, other factors (socio-economic, sociological) would seem to prevail in importance. There is no doubt that tsetse control causes not only an increase in agricultural but also in pastural productivity.
However, there is no proof of a general decivisive influence of these control measures on the utilisation of the land. That the natural resources are endangered is beyond dispute, regardless of the presence of tsetse control (compare Korhogo and Tortiya areas). This applies in particular to the gallery forests and the dense woodland.
FIGURE 2 Dynamics of Land-Use and Landscape Structure in the Study Area of the Tortiya Region with Tsetse Control since 1992 (based on aerial photos and field studies, size of the area examined: approx. 100–150km2)
In the region of Bouaké where tsetse control started in 1990 no drastic changes in land use or vegetation cover took place between the 50's and 90's (figure 3). The density of the rural population is currently stagnating and it is rather low in comparison to the two areas in the North and North-Central region.
FIGURE 3 Dynamics of Land-Use and Landscape Structure in the Study Area of the Bouaké Region with Tsetse Control since End of 1990 (based on aerial photos and field studies, size of the area examined: approx. 100–150km2)
4. EVALUATION AND FORECASTS FOR THIS AREA
The change in lifestyle of the two main ethnic groups in the Northern area under study, combined with the constantly in-creasing population density, is leading to a continuous expansion of arable agriculture and rangeland with simultaneous reduction in the fallow periods and overstocking. The most important human impacts in the Bouaké and Tortiya areas are the savanna fires and the deliberate fire clearings of the existing remaining forests. In the Korhogo area the fire factor is of secondary importance compared to agriculture and pasture-farming, due to the existence of less flammable grass biomass and the fact that the rejuvenation of the forests is generally not prevented to the same extent. Here, the increase in the size of the cattle stocks, com-bined with a reduction in the fallow cycles is leading to local degradation, with rising tendency. This development towards increasing degradation of the savanna through excessive utilisation of these natural resources could only, if at all, be stopped with appropriately adapted land-use planning and implementation control. This also involves the continuing destruction of the denser woodland and, above all, of the gallery forests. Thus, not only the full exploitation of the remaining natural areas, but also the increased utilisation of the marginal areas must be classified as ecologically questionable. In the area of the sub-optimal agriculturally-used areas within the area under study near Bouaké this process will take much longer to develope - also due to the current stagnation in population growth. However, without appropriate planning and the effective enforcement of corresponding measures, a similar development will be inevitable even in this marginal area. It is, however, well-known, and clearly confirmed by this study, that controlled pasturisation can, through the consequent change in the fire pattern, lead to an increase in woody plants and thus prevent a degradation of the savanna. But it is only a small step to excessive utilisation with overproportional cattle breeding and thus to long-term destruction of these biotopes as well.
5. INDICATORS OF THE RISK TO NATURAL RESOURCES
An evaluation of the ecological consequences of the documented changes in the land-use in the area under study should not only take nature and species protection into account but also the sustainability of the agricultural farming systems. Utilisation and nature protection can, depending on the angle of con-sideration, pursue opposite interests, but they can also form interest alliances. Opposite interests become apparent, for example, with regard to the enormous areas required for plant production, from which the natural forests mainly suffer, thus endangering the existence of forest-dependent animal and plant communities, already relegated to relict survival areas. However, at the same time, it can also be regarded as a reviving of natural resources which need not from the very beginning exclude the possibility of sustainable utilisation. On the other hand, support given to sustainable agricultural production is a direct contribution towards relieving colonisation pressure on the natural relict areas. This applies not only to agricultural but also to pastural production, whose sustainability is being endangered by bush-growth and regressive successions of grass cover.
These processes can be recognised and described in the forefront of visible changes through the observation of certain indicators. Ecosystem indicators of such anthropogenic changes could be:
Regular investigations on the ground and large-scale monitoring with the aid of aerial photos or satellite photos, permit effective ecological control using the above indicators.
6. IDENTIFICATION OF ENDANGERED ECOSYSTEMS
The term endangered or sensitive ecosystems is taken to mean those ecosystems which are either a priori especially susceptible to human impacts or those whose further existence would appear to be in danger through human influence. This can, in extreme cases, involve the destruction of a certain ecosystem or the reduction of such systems to more or less isolated habitat fragments. Sufficient size and continuity of certain habitats are the pre-requisite for long-term preservation of many species, in particular in the case of tropical ecosystems with the highest biodiversity. Particular importance must hereby be attributed to those types of ecosystem with a very restricted local distribution. In the Côte d'Ivoire this applies in particular to the savanna ecosystems which already have a long history of human impacts, especially with regard to the factor fire. Consequently, they are quite rightly often referred to as fire climax communities (cf. Cesar 1992).
From South to North the riverine gallery forests gain increased importance as relict areas. This is partly due to their high biodiversity, and partly due to the fact that, as a result of current human impacts, there are no longer any other comparable dense forest formations in these areas, which would be able to fulfill their function as refuge areas for forest-dependent species. Gallery forests are favoured for and thus especially endangered by the expansion of agropasturally-used areas (e.g. for the expanding rice plantations, or in the vicinity of fords and watering places but also (with Tortiya as an example) as a result of diamond-mining. The gallery forests have already been subject to considerable damage in many areas.
Over the past thirty years or so there has been a considerable general decrease in forest-covered areas in the whole of the Savanna zone. Of a former areas of approx. 47% of the Savanna Zone, which, after all, makes up almost 60% of the whole area of the Côte d'Ivoire, only about 9.5% are now covered with forests (Sayer et al. 1992) (cf. figure 4). In view of this trend, the protected areas already defined in the Savanna zone such as, for example, the National Parks, Fauna and Flora Reserves and Permanent Forest Domains (formerly “Forêts Classés”) gain great importance (ref. maps in Staurt et al. 1990, Sayer et al. 1992, IUCN/UNEP 1987, IUCN 1992). This also applies to smaller fragments of natural forest areas still existing outside of these protected areas, which from habitat islands for numerous animal and plant species. Up-to-date mapping of these forests with an ecological evaluation thereof, based for example on satellite photo interpretation, is still outstanding. Management plans for the protected areas which have already been created are, if at all, only at draft stage (Stuart et al. 1990, Sayer et al. 1992, FGU-Kronberg 1979 a,b) as is the case with the infrastructure required for their long-term maintenance. In most of these areas, similar to the above-mentioned example of the Forêt Classée de Badénou, there is already evidence of considerable anthropogenic changes which, at least in the Northern part-area, are directly or indirectly linked to changes in the transhumance pattern.
FIGURE 4 Estimates of total woodland, Permanent Forest Domains and conservation areas in the savanna zone of the Côte d'Ivoire (data from Sayer et al. 1992) (NB: conservation areas in the savanna zone exist only since 1968; estimates of total woodland in 1974 and of Permanent Forest Domains in 1990 are not available)
Seen as a whole, the only other protected areas within the areas under study are, apart from the Permanent Forest Domains, the Fauna and Flora Reserve “Haut Bandama” and - further away -the Comoe National Park. The fact that there is no extensive and, above all, connected system of protected areas in the Savanna zone of the Côte d'Ivoire, underlines the necessity for preservation of Permanent Forest Reserves and of the still remaining fragments of unprotected natural savanna and forest formations as elements towards the development of a connected system of protected areas. Detailed general monitoring advice can be found for example in McNeely et al. (1990).
7. CONCLUSIONS / RISK REDUCTION STRATEGIES
Sustainable use and preservation of the biodiversity are aims of equal standing, which can only be achieved jointly and not isolated from each other. The example of the Côte d'Ivoire demonstrates that, in the partly observable negative ecological developments, tsetse control is at the most a subordinate factor compared to the general social and economic development. It is therefore, sufficient to take the factor tsetse control into consideration within the scope of general environment monitoring in connection with the planning of land-use and its implementation. This may not apply to other areas of Africa. The reason for this is not to be found in elementary differences, but merely in the fact that the importance of tsetse control with regard to its influence on the natural resources is more dominant than other factors such as demographic, economic or sociological (ref. Jordan 1986, Stevenson 1988).
The tsetse control technique using odour-baited, insecticide-imporegnated traps/targets implemented in the Côte d'Ivoire represents, at present, an environmentally safe technique with low or negligible effects on non-target organisms. As a result of the new utilisation and settlement possibilities for new areas which thereby arise and consequent anthropogenic influences on the ecosystem, indirect negative effects on the environment cannot be excluded. It is, therefore, important to implement measures which enable early recognition of such negative impacts and thus avoidance thereof or which, at least, reduce them to an acceptable extent. The basis of such a risk minimisation strategy is a knowledge of the distribution, structure and dynamics of the ecosystems in the affected area, within the context of the relevant demographic, sociological and economic (including agricultural) determining factors.
An instrument well suited for the compiling, evaluation and influencing of agricultural/ecological changes is a long-term monitoring programme. This represents orientation to the actual dynamics and enables prompt realisation of knowledge gained in an ecologically-orientated development plan. Above all, developments with delayed effect can be recognised in good time with the help of indicators, thus enabling control measures at an early stage.
One of the most important components of long-term monitoring is the establishement of areas of constant observation. By means of simple data assessment methods (indicators) it is possible to document relevant changes in structure and extent of affected ecosystems and - upon determination of negative development trends - to introduce appropriate counter-measures in good time.
Such monitoring within the scope of tsetse control measures could make direct use of the optimal infrastructure of the Captureur system. In view of the almost total area-coverage of the campaigns carried out in Central and Northern Côte d'Ivoire, this would involve nearly full coverage of all important woodland and riverine forest areas. With the aid of simple evaluation sheets on the basis of easily-assessable indicators it is possible to maintain continuing data on the ecological status of the affected ecosystems. This would, for example, enable documentation of changes in settlement patterns within control areas as well as direct and indirect impact on forest and savanna ecosystems.
Land-use planning must include measures towards the protection and rehabilitation of endangered ecosystems as well as possible compensation measures.
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