Contents - Previous - Next

This is the old United Nations University website. Visit the new site at http://unu.edu

III. Wood resources and their use in the Nuba mountains

III.1. Energy and wood resources in Sudan and the Nuba mountains area
III.2. Physical characteristics of the Nuba mountains area
III.3. Wood resources and their use
III.4. Conservation policy
References

A. A. Babiker, H. A. Musnad, and M. Z. Shaddad

The first study - of aura and its parasite buds - was concerned with a national problem, that of the supply of the staple food for most Sudanese, and also a problem most acute in the arid and semi-arid parts of the country. The theme was the interrelation of humans, livestock, cropping, and a plant parasite within the context of nature/ resources In the second study - of the impact of improved water supplies in eastern Kordafan - the interrelationship was between humans, water supply, and land use As a result of the nomadic traditions of the area, not always now expressed in actual long-distance movement but still expressed in the social significance of livestock, the overriding interest in relation to natural resources has become pasture.

The three basic material needs of humans (and their animals are food, clothing, and shelter. The first two studies were concerned with food, but clothing is also included in crop growing (cotton) and animal rearing {wool and hair). The third study deals with shelter. Tents may be made of wool and hair and huts of sorghum straw, but wood products are the most important in Sudan for house construction, as well as for furniture making and fuel (either directly as firewood or as charcoal).

In arid and semi-arid regions with a rapidly rising population experiencing movement to the towns, the demands for wood fuel rapidly escalate. Locally available supplies are necessarily limited and are often soon exhausted. High prices caused by a high urban demand means that wood supplies may be brought in from increasing distances, with potentially serious effects on the environment In periods of unusually severe drought, as from 190-8 to 1973, large numbers of rural cultivators and workers became destitute because of crop failure and loss of animals. Such people look to the natural environment first of all for an alternative source of subsistence. Chopping down trees for sale is one possible temporary solution to urban migration, especially for the destitute nomad. Such a situation has been experienced in North Kordofan Province (Digernes 1977 and 1978). South Kordafan is damper and has a reasonable forest cover in the Nuba Mountains, but its wood resources too have come under an increasingly severe strain in recent years.

The first paper showed that the reasons for the nonacceptance of known methods of buds control were related to a lack of know-how, severe doubts about the economic viability of control methods, and the high risk of famine involved with their implementation. The second paper pointed out the problem posed by different outlooks and attitudes to water and development on the part of planners on the one hand and the resource users in the other. This paper now investigates the interplay of economic, social, and environmental factors which inhibit "rational"use of wood resources in the Nuba Mountains.

- H. R. J. Davies

III.1. Energy and wood resources in Sudan and the Nuba Mountains area

The problem reviewed
Wood resources and the demand for energy in Sudan
The study

The Problem reviewed

The interaction between human beings and the natural environment is a highly complex one. Changes in the level of human technology or in economic and social organization have important impacts on the natural environment. Similarly, changes in the natural environment will in turn have their impact on human economic and social life and institutions. In areas where rapid change takes place in one of the elements but not in the other, a dangerous imbalance may occur with potentially disastrous results for people and/or the natural environment. This is a problem for both "developed" and "developing" societies. However, the greatest potential for disaster lies in "developing" areas with rural societies in marginal environments. The result of a downward fluctuation in the rainfall of the savanna lands of Africa during the Sahel drought of 1968 to 1973 was famine and human hardship and the loss of large numbers of livestock. For such an environmental change there were clearly too many people and too many animals occupying the affected lands. The solutions available to the rural cultivator and herder were either to try to hang on until things improved, to migrate to another rural area capable of supporting the same way of life, to adopt a new way of life in the rural area, or finally to move to a town.

In the Sudan all solutions were attempted, but each of them has potentially deleterious environmental effects. Either hanging on or adopting some alternative form of rural life under such circumstances is likely to increasingly seriously deplete the local natural resources, while migration to another rural area merely raises the possibility of over use of natural resources elsewhere. Even moving to an urban area creates environmental problems, because increasing urban populations make heavier demands on the food and wood fuel supplies of locally small areas around them and an ever-increasing, outward-spreading circle of rural resource depletion develops.

FIG. 1. Resource use in rural Sudan

Though environmental fluctuation may be an important phenomenon, other factors can have equally, or even more, disastrous results. These include increasing pressure on the land from an increasing population of people and animals and imbalances created by the introduction of modern forms of mechanized agriculture which may either be unsuited to the natural environment or be introduced without the necessary accompanying changes in economic and social life and institutions.

An understanding of some of these difficulties and interactions is a prerequisite for sound planning. A pattern of interaction for rural Sudan is shown in figure 1. From the model it is clear that the environment provides certain components to be used by the rural population. Imbalance between the degree of use and the rate of regeneration of resources can lead to one or more of the following ecological impacts: deforestation, over-grazing, and soil erosion, which in turn also have socio-economic ramifications.

Different kinds of lines are used in the model to indicate major female or male activity. It is clear that women in the rural areas, through their many and varied activities, have more contact with the natural resources than do men. This alone is an important point for planners to consider. It is apparent that, if more attention is paid to rural women, it is more likely that conservation of our national resources will result, especially in the more arid environments.

In relation to wood resource use, the subject of this paper, figure 2 shows rural energy use and its probable impact on the environment. Input into the system is the demand of the household, which is governed by family size and income. Depending on the availability of resources and access to them, the individual may have certain alternatives to choose. The choice of one or another or more than one source of energy has in turn certain different effects on the environment. These could be negative, such as deforestation or soil erosion, and will have an effect on the regrowth or rate of regeneration of the vegetation. This in the end would have its effect on the choice again. The general pattern of use and the degree of pressure on the resources are again affected by the environment and the socioeconomic level of the society.

FIG. 2. Rural energy use and its environmental impacts

This system is entirely dominated by women, since they are the only gatherers and users of energy at the same time. This is again an important point to consider for environmental planning.

Wood resources and the demand for energy in Sudan

Sudan is essentially poor in energy. The energy consumption figure for Sudan in 1980 (including all forms of energy used) was estimated to be 5.1 million tons of oil equivalent. In international terms this is low, but it represents more than a sevenfold increase over the last 20 years. During the 1960s the average annual rate of growth of energy demand was about 10 percent, while that of the GNP for the same period was only 3.6 per cent (Shulli 1978).

At present the main sources of energy are wood fuel, imported fossil fuels, and to a much smaller extent hydroelectric power. According to a recent report (Sudan Government 1981):

- wood fuel (firewood and charcoal) accounted for 75.1 per cent of the energy consumed in Sudan in 1979/80;
- fossil fuels, 21.6 per cent; electricity, 1.0 per cent;
- crop residues and animal refuse,1.4 per cent;
- animate energy, 0.9 per cent.

More details about the quantities, costs, and the share of each source are found in table 1. Fossil fuels and electricity generated thermally or hydro-electrically constitute the only commercial sources of energy. Petroleum products are consumed mainly as energy input in the modern sector of the economy, such as transport systems, mechanized and irrigated agriculture, and industry.

The increase in the consumption of oil products during the 1970s was 6.3 per cent per year, but a much higher rate of increase is expected during the 1980s. Since the official domestic demand estimation for 1985 gives a figure of 3 million metric tons of oil, to supply this increasing demand with rising oil prices will lay even heavier pressure on the balance of payments. In 1981 the oil bill accounted for about 90 per cent of the total value of export earnings.

Electricity is used largely in association with the larger urban areas for residential use and manufacturing but also to some extent in rural electrification, and along the Niles in Khartoum Province in particular for irrigation. Of the total power generated, about 26 per cent was thermally produced from 17 isolated stations and about 74 per cent was produced from three hydro-electric power stations (table 2). The Blue Nile Grid System alone distributes more than 80 per cent of the total generated electrical power. It links the two major hydro-electric stations of Roseires and Sennar with the major load centres in the provinces of Khartoum, Gezira, and White Nile.

TABLE 1. Energy consumption in Sudan, 1979/80

Source: Sudan Government 1981

TABLE 2. Electricity generation in Sudan, 1979/80

Source: Sudan Government 1981

A serious inadequacy exists between the current demand and supply of electricity. Whereas the annual growth of demand between1974/175 and 1979/80 was 13.8 per cent, that of the overall electricity generation was only 10.5 per cent. Such an imbalance represents a major constraint in productivity and growth, especially for the industrial sector.

Wood-based energy sources are mainly used in the rural areas. More than 90 per cent of the households in Sudan use wood as a primary source of energy for cooking and other household purposes. The most significant feature is that wood-based sources of energy provide 75 per cent of the total energy consumed in the country (table 1). From the total amount of 10.65 million tons of firewood consumed in 1979/80, 98 per cent was utilized as household fuels and in domestic services and bakeries, mostly in rural areas. The remaining 2 per cent was the only available fuel for rural industries such as brick-burning, pottery, tobaccocuring, and the production of steam for processing vegetable oils (Sudan Government 1981).

Charcoal, on the other hand, represents the main household fuel in urban areas. The amount consumed in 1979/80 was 550,000 tons, produced mainly by primitive methods with a very low recovery rate.

Almost all the firewood and charcoal was obtained from natural forests, which occur in the Sudan under different ecological conditions. The total volume of naturally growing stock is estimated at 1,333 million m, while that of man-made forest plantations is 8 million m³. The estimated annual increment of the whole growing stock is 5 per cent, which would allow a total removal of about 67.05 million m³ per year. This figure is subject annually to losses from bush fires, drought, grazing, and the expansion of mechanized agriculture amounting to about 4.75 million m³. From the remainder some 8.7 million m³ are used for sawn timber, round timber, and poles. This leaves 53.6 million m³ for wood fuel.

The available wood resources are unevenly distributed within the country. Mukhtar (1978) reported the following distribution of wood fuel resources by region:

- region A (Red Sea, Kassala, Northern, Nile, and Khartoum provinces), 5.0 per cent;
- region B (Blue Nile, Gezira, and White Nile provinces), 22.4 per cent;
- region C (Northern and Southern Kordofan and Darfur provinces), 29.3 per cent;
- region D (Eastern and Western Equatoria, Bahr el Ghazal, Lakes, Upper Nile, and Jonglei provinces), 43.3 per cent.

If this distribution is compared with that of the population and the distribution of Sudan's rapidly expanding urban areas, it is evident that there is an inverse relationship between population distribution and the rate of urbanization on the one hand and the distribution of wood resources on the other: the regions with most population and highest rates of urbanization (regions A and B) lack enough wood resources to satisfy their growing demands.

This in turn means that more pressure will be exerted on the resources of the two other regions, especially those of region C because of its relative accessibility to areas of greater demand. The largest per capita consumption of energy comes from Khartoum Province. Southern Kordofan, including the Nuba Mountains, lies in region C.

The study

Although the wood resource supply in many areas of Sudan may perhaps seem sufficient to satisfy the needs of local rural communities, the combined demand of both rural and urban households seems to be beyond the capacity of the available accessible natural forests. With increased urbanization more wood fuel would be used, especially converted to charcoal with a very low recovery rate (less than 15 per cent). Moreover rural people, faced with energy shortfalls and high fossil fuel costs, will rely more and more on forestry resources to meet their energy needs for domestic use and to satisfy their need for shelter, raw material for home industries, etc. With declining forestry resources and an inability to find access to other fuels, rural households will increasingly rely on an expanded production and consumption of various other organic materials such as crop and animal residues to meet their energy needs. In the absence of forestry conservation and development policies, environmental deterioration is inevitable (Babiker and Abdou 1981). This study attempts to analyse the crucial components of the relationship between rural wood resource use and the environment. In particular it focuses on the use of wood by rural households for energy, to determine the actual potential available for local use while maintaining ecological stability. Its main objectives are:

a. to study the existing forest resources and suggest possible measures for conservation with the aim of maintaining the tree cover;
b. to map the distribution of forest types and economically useful individual tree species and, if possible, determine their productivity under various management regimes;
c. to identify the major problems of wood resource use, especially the maintenance of wood fuel supplies; d. to examine the current forest management strategies and to identify the obstacles to the application of proper forest management procedures.

The area chosen for analysis is that part of Southern Kordofan Province Iying approximately between latitudes 11 and 12° N and longitudes 28° 30' and 31° E (figs. 3-5). A variety of kinds of data were gathered. The biomass was identified using aerial photographs, satellite imagery, and ground checks to distinguish and classify vegetation patterns and to identify areas of solid rock outcrops, semilaterized soils (gardud), and clay plains. A detailed survey of household consumption of wood and fuel availability (by quantity, quality, and price) was carried out to under stand the socio-economic situation. The survey used 396 questionnaires, completed in March 1980, distributed in three smaller areas within the overall Nuba Mountains study area (fig. 3), as follows:

- area A, Kalkada-Heiban (a "remote" area), 153 respondents;
- area 8, Lagawa-Berdab (an "intermediate" area), 129 respondents;
- area C, Habila-Delami (an "inaccessible" area), 115 respondents.

FIG. 3. Location of the study areas

Other data were collected from sources such as the Ministry of Agriculture, especially the Forest Department, and from regional government offices in the study area. Without this basic information sound ameliorative planning cannot take place.

III.2. Physical characteristics of the Nuba mountains area

Geomorphology
Climate
Soils and vegetation

Geomorphology

The Nuba Mountains area is an uplifted part of the crystal line basement complex composed mainly of gneisses with some crystalline schists, marbles, and mete-volcanics. It is surrounded to the east, north-east, and south by the Umm Ruwaba graben (fig. 4). The latter is filled with unconsoli dated Plio-Pleistocene sediments of riverine and lacustrine origin. To the west the area is bounded by a large north-east south-west-trending fault marked by the valley of Wadi el Ghalla, while on the north it is bounded by a system of structures with north-east south-west, east-northeast west-south-west, and south-east south-west trends which determine the location of Khor Abu Habl and its tributaries (fig. 4). On the east the area is bounded by a plain gently sloping towards the White Nile. On the south the faulted contact with Nubian sandstones and Umm Ruwaba sediments is marked by marshlands and lakes, including the Sudd and Lakes Keilak and Abyad.

The geomorphologic features of the Nuba Mountains area itself have been formed under two influences: the block faulted structure of the basement and the repeated differential movement of earth blocks, due to the processes of tectonic activity responsible for the formation of the Umm Ruwaba graben and the East African Rift System. This differential movement together with subsequent erosion is responsible for the present appearance of the land surface with its attendant soils and vegetation.

The Nuba Mountains area can be subdivided into four geomorphic units: (1) the mountainous areas, (2) inselbergs, (3) the clay plains, and (4) the drainage system and related neotectonic phenomena.

The Mountainous Areas

The mountainous areas are regions of rugged, highly dissected terrain including the Rashad and Heiban massifs, the Gulud Hills, and the Botha massif. The first two are elevated areas with relief reaching up to 500-600 m above the plain (about 700-800 m above sea level). The high hills are mostly ridges separated by narrow V-shaped valleys controlled by rock structure, lithologic variations, and faulting. In the Rashad massif a broad plateau occurs in the centre with an average height of 300 m above sea level. The Botha massif is an area of only slight uplift, leading to very subdued contrasts in relief between the narrow ridges separated by shallow V-shaped parallel depressions. The ridges are partly buried rocky outcrops, and the troughs are filled with partly transported colluvial clays.

FIG. 4. Geomorphology of the Nuba Mountains

FIG. 5. Soils and vegetation of the Nuba Mountains (potential vegetation and soil units described in text)

The Gulud Hills are different from the other mountainous areas since they consist solely of granites. The geomorphology is dominated by numerous conical hills, often with imposing domed landforms. They are rather low, having heights not exceeding 100 m above the surrounding plain.

Inselbergs

Inselbergs are isolated hills, ranging from individual small hills to large compact massifs covering areas in excess of 450 sq km. Most of the inselbergs, such as the younger granite and syenite masses, were formed by a process of differential erosion, since they are usually much more resistant than the surrounding gneisses. Smaller inselbergs such as those of Keiga Luban halfway between Kadugli and Dilling are simply remnants of the largely peneplain surface.

The most important group of inselbergs are those extending in a west-north-west belt from Talodi through Kadugli to Lagawa. These are mostly composed of syenite and granite, often with ring structures and sometimes consisting of multiple granitic and syenitic intrusions, as at Masakin, Tira, Limon, Miri, and Sileichi.

The external form of these inselbergs is dominated by imposing steep sides, often with typical domed forms. The overall profiles of inselbergs fall into three categories: simple cone shapes; caldera-like shapes conditioned by the occurrence of resistant rings around less resistant rocks, as for instance Jebel Kinderma in the eastern part of the Tira-Limon group, Jebel Talodi, and Jebel Sileichi near Lagawa, and those with more or less table-like tops, such as Jebel Tabag and Jebel Kakada north of Lagawa and Jebel Doro.

The steep drop on the sides of the hills has considerably influenced the character of deposition of stream sediments. They facilitated the formation of narrow pediments of ill-sorted material surrounding the hills. These pediments, which were later weathered in situ, are an excellent source of near-surface ground water and have thus considerably influenced the pattern of human settlement and vegetation growth.

The Clay Plains

The clay plains occupy a considerable part of the Nuba Mountains area. Most of them are covered by fertile black clays known locally as cotton soil. The plains may be subdivided into peripheral and inter-montane plains. The peripheral plains surround the area from all sides and are characterized by weak denudation, as on the gardud plains north of Khor Abu Habl or the sands west of Wadi el Ghalla, and partial stabilization of materials, as on the plains to the south-west and west of the Nuba Mountains. A large area of deposition occurs in the Abu Habl delta, where wind-blown sands have encroached on the parts of the peripheral plains across Abu Habl and to the west of Wadi el Ghalla. Intermontane plains are largely clay plains forming the surfaces of tectonic blocks, some of which are experiencing neotectonic movements. Despite their relative low position the intermontane plains are being actively eroded from all sides. This is why these plains are not as flat as those to be seen in similar situations elsewhere in Sudan. Their surface is usually undulating with slope angles varying from 0 to 15 degrees. The greatest local undulations are encountered in areas of active differential movement of blocks.

The peneplain blocks are rectangular (Habila), isometric (east of Delami), or elongated side by side in the manner of piano keys (north and east of Dilling, south of Jebel Umm Heitan) (figs. 3, 4, and 5).

The Drainage System

The drainage system is closely related to the original fault pattern of the area, the tilt of the land, and the neotectonic movements affecting the area. The major water divide, that between the White Nile and Bahr el Arab, crosses the area diagonally, passing a little south of Dilling, through the Habila Scheme, and along the northern slope of the Heiban massif to the area of Kalogi in the south-east. Generally speaking, the drainage system related to Bahr el Arab is denser than that of the White Nile, which is intensified only locally along the upper reaches of Khor Abu Habl. Thus it appears that the general tilt of the land surface is greatest in the direction of Bahr el Arab. Higher-order streams in the plains are characterized by their linear appearance and parallelism, being directly controlled by the fault pattern. The drainage system along the upper reaches of Khor Abu Habl is angular.

The linear and angular patterns are more pronounced in areas of later neotectonic movements where the superficial cover is just being eroded. Under these conditions dendritic and trellis patterns are developed within low-order streams, particularly second- and first-order streams. In areas of earlier developed neotectonic movements where the superficial cover is largely removed and basement rocks have been well dissected, as in the north part of Wadi el Ghalla, a dendritic pattern is developed even among higher-order streams (fig. 4). This peculiarity of the drainage system is well expressed in satellite images of various scales. Thus the linear and angular pattern of the Abu Habl is prominent, while that of Wadi el Ghalla is masked by the extremely dense dendritic pattern of high-order streams. The dendritic pattern and incipient gully formation in the Abu Habl system are observable only in aerial photographs.

The effects of neotectonic movements are well expressed in topography. Differential uplift leads to the formation of very gently undulating topography in the relatively lower blocks, where the ground slopes gently towards the khors, normally with between 5 and 10 degrees of slope. Relatively elevated blocks are characterized by more sharply undulating relief with a range of 10 to 15 degrees of slope. Naturally such blocks are eroded to some degree, and this is expressed in the character of the superficial deposits.

Any account of the drainage system is incomplete without mention of the broad fault-controlled valleys. Such valleys are particularly important in the eastern Nuba Mountains- e.g. Khor Shwai, Khor Agab, and Khor Umm Abdalla. These khors are usually exceptionally wide, with Khor Shwai for instance reaching about one kilometre in width. They are important areas for horticulture and form the natural habitat of doleib and dom palms.

Of the areas chosen for detailed study, areas A (Kalkada-Heiban) and B (Lagawa-Berdab) are essentially hill massif areas with associated inselbergs and clay plains, while area C (Habila-Delami) is one of clay plains with inselbergs.

The geomorphological and geological characteristics of the Nuba Mountains area-differences in Ethology, slope structure, stream patterns, and the occurrence of neotectonic movements-play an important part in the erosional processes determining the nature of the soils and their potential for supporting various kinds of vegetation, including tree species, the primary concern of this study.

Climate

A further basic element in the process of soil formation and destruction is the climate.

The plains are hot throughout the year, with daily minima rarely falling much below 15°C and daily maxima frequently exceeding 35 C. With altitude on the hills, these figures are somewhat reduced. In the south the lowest monthly means temperatures occur in January during the dry season and in August at the height of the rains. Further north the tendency is for the lowest means to occur in January and February.

Rainfall varies considerably from year to year, with a mean annual variability of about 15 per cent overall, tending to rise somewhat towards the north. At Kadugli the average rainfall, 1941-1970, was 731 mm per year, with six months exceeding 25 mm. Further north, at El Obeid, the average annual total for the same period was 386 mm, with only four months averaging more than 25 mm (fig. 6). The difference between north and south is also reflected in the wind directions, with northerly and southerly winds dominating for six months each at Kadugli but with northerly winds dominating increasingly towards the north.

FIG. 6. Temperature and rainfall at Kadugli and El Obeid

Under such conditions it is not surprising that transpiration rates are high, exceeding precipitation for some 10 months of the year, and the relative humidity rates are low. At El Obeid the mean humidity at 2 p.m. exceeds 50 per cent only in August and at Kadugli only in July, August, and September.

Contents - Previous - Next