Bernard N. Kigomo 1
The African dry forests and woodlands cry for attention as they continue to degrade and desertification to set and intensify. Africa is the driest of the world continents with 45% of its landmass falling under dry lands. Furthermore 38% of this land is occupied by hyper-arid or desert land. About 50% of the African population lives in the arid, semi-arid, dry sub-humid and hyper-arid areas.
A total of 340 million ha of woody vegetation in dryland zones of Africa have become degraded through human activities like; overgrazing, agricultural expansion, overexploitation, and deforestation, in the order of importance. Small-scale farming activities in the dry areas have, in particular, caused the greatest impact on vegetation degradation. Frequent fires and droughts have continued to accelerate degradation of woodlands and dry forests.
About 482 million ha of drylands in Africa have suffered desertification through several physical factors. Such physical agents of desertification includes, in the order of importance; wind erosion, water erosion, loss of nutrients, salinisation, land compaction and water-logging.
Very few case studies have been followed for enough time to provide adequate data to enable effective interventions. Methodologies for monitoring extent and impacts of agents of degradation and desertification also vary greatly. Regional and local initiatives geared towards rehabilitation of the degraded vegetations need to be urgently identified and focused support by partners provided.
Degradation of natural resources eventually leading to desertification is more pronounced in Africa than any of the other contents of the world. Africa is dominated by the Sahara Desert in the north and the Namibian and Kalahari Deserts in the south, contains a preponderance of hyper-arid and arid lands, which are mostly unsuitable for agricultural activities. About 45% of the landmass in Africa is dry land and is comparable only with Asia, which has 39% of its landmass as dry land indicating that Africa is the driest of the world continents. Aridity zones for Africa have been calculated using the high-resolution climate data (Corbett at al. 1996; UNSO/UNDP, 1997). The regional level statistics are summarized in Table 1 below.
|Table 1: Area per aridity zone by sub-region for Africa (Area numbers are in thousands of km 2 )|
|Source of data: Corbett, 1996; UNSO/UNDP, 1997|
The total African aridity cover according to high-resolution assessment used to produce Table 1 is about 21.2 million ha. 38% of this area is, however, occupied by the hyper-arid category, which is largely located in the Northern region. The second in importance of the aridity categories is Semi-arid which takes up 29% of the total aridity area of Africa. With the exceptional of the Central African region and slightly ragging behind, the Southern Africa, the other three regions, i.e. Northern, Western and Eastern regions have almost equal total cover of aridity areas (Table 1). Central Africa is largely forested and contributes to only 1% of the total aridity zone of Africa.
Northern African countries considered in the aridity computations includes; Algeria, Egypt, Libya, Morocco, Tunisia and Western Sahara. Western Sahara is 100% hyper-arid, Egypt 95% hyper-arid, while Algeria and Libya are each over 80% hyper-arid.
Western African countries with substantial covers of aridity zones include; Chad, Mali, Mauritania and Niger. Cote d'Ivoire, Guinea-Bissau, Liberia, Sierra Leone and Togo, also in Western region have none or very little cover occupied by the arid zones. Benin, Gambia, Ghana, Nigeria and Senegal have some of their areas covered by Semi-arid and Dry Sub-humid aridity categories.
Central African countries include; Cameroon, Central Africa Republic (CAR), Congo, Equatorial Guinea, Gabon and Central Republic of Congo. Cameroon is 1% arid, 8% semi-arid and 8% dry sub-humid. CAR is 5% semi arid and 7% dry sub-humid. Only 3% of the CRC has dry sub-humid aridity category. The other three countries of Central African region have no aridity zones.
The Eastern African countries include; Burundi, Djibouti, Ethiopia, Kenya, Rwanda, Somalia, Sudan, Tanzania and Uganda. Hyper-arid, Arid and Semi-arid zones largely occupy Sudan, Djibouti and Somalia. Kenya and Ethiopia have large areas occupied by the arid and semi-arid zones while Tanzania and Uganda have largely semi-arid and dry sub-humid dry land zones. Burundi has only 5% of its land area covered by dry sub-humid zone. About 51% of Tanzania is relatively dry while over two thirds of Kenya falls within arid and semi-arid zones where 33.3%, 51.8% and 12.3% of this land experience slight, moderate and severe hazard levels of land degradation respectively (UNEP, 1997).
Namibia and South Africa have large areas of arid and semi-arid categories but also have 8% and 1% occupied by hyper-arid zones respectively. Also covered by the two arid categories are Angola and Botswana. South Africa has 12% of its land area covered by the dry sub-humid zone. Lesotho, Malawi and Mozambique have between 50 -55% of their land covered by the semiarid and dry sub-humid zones. Zambia and Zimbabwe are largely covered by semi-arid and dry sub-humid dry land categories.
Removal and degradation of vegetation cover is common in the dry areas of Africa and this directly leads to soil degradation after exposure. Deforestation and removal of natural vegetation is increasingly caused by various human activities. The extent of such woody vegetation degradation as a result of human activities is shown in Table 2.
|Table 2: Extent of land Degradation due to Deforestation and de-vegetation in Africa (million ha)|
|Source: World Atlas of Desertification, 1997|
Overgrazing is the most notable factor in causing de-vegetation and hence degradation. The heaviest impact of overgrazing takes place in the Sahel countries especially areas falling within the Arid and Semi-arid zones (Table 2). Overgrazing is concentrated around settlements and is often related to recent sedentarisation of nomadic herders. The extent of degradation in semi-arid zones is more influenced by agricultural activities than in Arid and Dry sub-humid zones while over exploitation in Arid zone is more important in natural resource degradation. Agricultural and deforestation activities are also important factors of soil degradation in dry sub-humid zones. A total of about 332.3 million ha of land in dryland zones has its soils eventually degraded through the four human activities (Table 2). Human activities in forest areas surrounding the drylands help to extend areas that become more vulnerable to soil erosion. Table 3 better illustrates the role of deforestation, especially for purposes of agricultural activities and new settlements.
|Table 3: Net Forest Area changes (1990-2000) in Africa by Sub-regions (area in `000)|
|Data source: FAO 2001|
Except in North Africa, all the other sub-regions of Africa suffered net losses of forestland during the last decade. The countries in the North Africa gained the small net forest cover through tree planting with Egypt having the highest increase of 3.3%, Algeria 1.3% and only Morocco had a non-significant net decrease of its forest cover. During the decade North African sub-region planted a total of 1,693,000 ha, which is 27% of the total forest cover in the sub-region (FAO, 2001). In Western Africa only Gambia had a net forest cover gain of 1.0% during the decade. This sub-region experience one of the highest growth of urban population and this has caused deforestation in the immediate vicinity because of increased forest exploitation for fuel wood and building materials while settlements continue to increase (Bellefontaine et al. 2000; FAO 2001). Swaziland in the Southern Africa region had a net forest gain of 6000 ha or 1.2% during the decade. Countries in the south lost much land through deforestation and few efforts were made to compensate the losses through afforestation programmes. A country like Tanzania has continued to loose about 500,000 ha annually through deforestation (Munyanziza, 2001). In 1980s the annual deforestation in Burkina Faso was 50,000 ha for the purpose of expanding agricultural land (Middleton and Thomas 1997). Deforestation in Niger has been so high that this has contributed to serious threat on the population of giraffe, which numbered only 100 individuals in mid 1990s from a much high population (Ciofolo, 1995).
Africa's closed canopy forests were being cleared at a rate of 0.8 per cent, with West Africa, West Sahel and East Sahel recording rates of 2.1, 0.9, 0.8 per cent respectively (Rasheed, 1996). The fastest rate of deforestation is occurring in West Africa where 4% of the closed forests is being cut down every year. Between 1900 and 1980 Cote d'Ivoire closed forests dropped from 14.5 million ha to 4 million ha, indicating an annual rate of deforestation of 300,000 ha. Uganda had 40% of its land covered by tropical forests by 1900 but this had dropped to only 3% by 1993. It is estimated that Burkina Faso, Burundi, Chad, Ethiopia, Gambia, Ghana, Guinea-Bissau, Liberia Mauritania, Niger, Rwanda, Senegal and Sierra Leone have already lost over 80% of their total forest land. Countries that have lost between 50 to 80 % of their forest cover since the turn of 20 th century includes, Benin, Botswana, Cameroon, Central Africa Republic, Cote d'Ivoire, Equatorial Guinea Guinea Bissau, Kenya Lesotho, Madagascar, Malawi, Mozambique, Nigeria, Somalia, Sudan, Swaziland, Togo, Uganda, Republic of Congo and Zimbabwe (Rasheed, 1996).
The extent of deforestation of forests, and therefore initiation of land degradation to the extent described above, has been largely attributed to the rising need for agricultural land especially around the fridges of dry areas. Analysis by FAO (2001) revealed that 4% of forests were deforested for shifting cultivation into undisturbed forests, 8% through intensification of agriculture in already shifting agricultural areas, 60% as direct conversion of forest area to small-scale permanent agriculture, 12% as direct conversion of forest area to large-scale permanent agriculture and 17% for other purposes like settlements etc. In the whole African continent only 8% is considered as gain in forest area during the last decade and this included also open areas that gained in canopy cover as reflected by satellites images analysis (FAO 2001). It is apparent from this analysis that the so common small-scale farming activities in the sub-humid, dry sub-humid and dryland areas has a serious impact in initiating and accelerating land degradation and to the extents shown in Tables 2 and 3 above.
In general and in addition, the combination of overgrazing, droughts, human population and choice of land use have been argued to play an important role in the extent of degradation of vegetation and soil conditions (Middleton, 1997; Middleton and Thomas, 1997). The contribution of population in degradation of natural resources is more apparent when the effects of drought incidences and various types of land uses reported in Tables 2 and 3 above are taken into consideration.
Data on fire incidences and intensities in Africa is inadequate to facilitate useful and comprehensive analysis of its contribution to land degradation (FAO 2001). Information on forests, woodlands and grasslands fires is therefore grossly missing yet fire is an important factor in the maintenance of vegetation cover and degradation in drylands. Although areas burnt by fire may sometimes recover after the onset of rains, a combination of fire and drought, which is a common phenomena in drylands of Africa will usually lead to serious degradation of vegetation and eventually to land degradation. Fire incidences, some of them very bad, are common in the entire African continent but more so in the dryland zones. During the 1986-87 dry season, for example 120,000 ha of forest and woodlands (which is 30% of total area of Burkina Faso) was burnt in Burkina Faso and such a disaster causes a heavy loss in terms of plant and animal resources and, induces land degradation.
Degradation of vegetation exposes soil mantle to further degradation. The major soil degradation agents in the African dry zones are wind erosion (52%) followed by water erosion (30%), then by loss of chemical nutrients and salinisation (10%) and physical compaction (8%) (Middleton and Thomas, 1997). Water logging play only a small role in soil degradation of the semi-arid and dry sub-humid zones. Erosion by wind is more prominent in the arid areas but has about the same effect in the semi-arid zone. Water erosion is the more important agent of soil erosion in the dry sub-humid zone. Due to high population of livestock in the semi-arid zone, soil compaction is greatest here than in the other dry zones. Some 480.5 million ha of drylands in Africa are thus exposed to degradation by wind and water erosion in addition to loss of nutrients, physical compaction and to a less extent water logging. Soil erosion will inevitably lead to desertification.
In very few cases are annual rates of land degradation in Africa been reported with certainty. This is mainly because only a few case studies have been followed for sufficient number of years that would allow evening out of the annual variations in records. In most of the cases reported gaps of information have been pointed out and more data and improvement of methodologies have been urged (UNEP, 1992; Middleton and Thomas, 1997; FAO, 2001).
As a result of variability of methodologies used and prevailing conditions of natural resources, estimates of rates of degradation are generally very different even in areas close together. Table 4 attempts to summarize reported estimates of desertification/degradation rates for several countries and areas.
|Table 4: Estimates of Annual Degradation/Desertification Rates in Several Countries of Africa|
|Country||Site/Locality||Aridity zone||Rate %||Remarks|
|Two study sites using the same methodology|
|Two study sites using the same methodology|
|Mauritania, Mali, Niger||Sahel||Sahel||0.6||2 million ha was the collective annual rate of degradation for the three Sahel countries between 1961-1987|
|Tunisia||Drylands||Dryland||10||Annual loss of productive land to desert, mainly through grazing|
|Source of data: UNEP 1992; Middleton and Thomas 1997; FAO 2001|
As observed briefly in Table 4, the rates of degradation vary greatly, from 0.03 to 10%. What is more apparent from the results is that the more arid the area the higher the rate of desertification.
In a more general study conducted in 50 countries affected by desertification, in 1989, by UNSO through a questionnaire, half of the countries reported to have experienced significant worsening situations - falling ground water levels, evaporation of surface waters, rangelands degradation, rain fed and irrigated crop deterioration and deforestation. 17% of the countries rated the desertification situation as being slightly worse. A similar study by UNEP in Southern Africa in 1989 concluded that the situation is worsening through out the entire Southern Africa region (UNEP, 1992). In both situations it is more likely that the situation is presently even much worse, one decade later.
The dryland woodlands and forests in Africa are seriously degraded and desertification has intensified more widely and at fast rates. The information synthesized above indicates serious extent of degradation and desertification for the various regions of Africa. It is necessary therefore that focused initiatives be embarked on to mitigate the ever-worsening levels of dry forests and woodlands degradation. Such efforts need to be implemented at regional and local levels and international communities and partners need to be more sensitive to the present situation and come to the support of the African governments and the affected people.
Bellefontaine R. Gaston, A. & Petrucci, Y. (2000). Management of natural forests of dry tropical zones. FAO Conservation Guide No.32, Rome.
Ciofolo I. (1995). West Africa's last giraffes: the conflict between development and conservation. Journal of Tropical Ecology 11, 577-88.
Corbett J. D., R.F. O'Brien, E. I. Muchugu and R. L. Kruska (1996). Data exploration tool: a tool for spatial characterization. CD-ROM and User's Guide.
FAO (2001). Global Forest Resources Assessment 2000. FAO Forest Paper, No. 140. FAO, Rome.
Horstmann B. (2002). Desertification - a worldwide problem. In: Agriculture and Rural Development: Volume 9 No. 1/2002. Eschborner, Germany.
Middleton N. J. and D. Thomas (1997). World Atlas of Desertification. UNEP, Arnold, London. UK.
Middleton N. J. (1997). Desert dust. In Thomas D.S.G. (Ed): Arid zone geomorphology: process, form and change in drylands. 2 nd edit, Chichester: Wiley, New York.
Munyanziza E. (2001). Afforestation of semi arid areas of Tanzania: focusing on the root compartment. In: Combating desertification with plants. Kluwer Academic publishers, New York.
Rasheed, S. (1996). The challeges of sustainable development in 1990s and beyond. In: Sustainable development beyond rhetoric- Africa environment. Environment Studies and regional planning Bulletin. Vol X, 1-2. Dakar 1996.
UNEP (1992). Status of desertification and implementation of the UN Plan of Action to combat desertification. UNEP/GCSS.III/3.
UNEP (1997). National Land degradation assessment and mapping in Kenya. Kenya Government, Royal Netherlands Government and UNEP. United Nations Office, Nairobi.
UNDP/UNSO (1997). Aridity zones and dryland populations: an assessment of population levels in the World's drylands. UNSO/UNDP, New York.
1 Kenya Forestry Research Institute,
P. O. Box 20412, Nairobi.
e-mail: [email protected]