|United Nations University - Work in Progress Newsletter - Volume 12, Number 1, 1989 (UNU, 1989, 12 pages)|
By Festus D.K. Bagoora
In the highlands of Uganda - a rugged terrain characterized by sharply pitched slopes and deep valleys - are found some of the greatest population densities in East Africa. This is due to historical factors going back over some centuries, as well as to the favourable climate and soils of this tropical, humid and fragile environment. But human activities in recent years - chiefly increased cultivation on steep mountainsides - have denuded the land and triggered an inevitable process of erosion, landslides and other deterioration of one of the globe's most precious resources: top soil. This is a sad and familiar story that research on highland-lowland interactions, by UNU and others, has been recording, with only minor variations, in many parts of the world.
Repeatedly stressed in these investigations is the need for improved scientific understanding of the world's highland ecosystems (and their interactions with lowland systems). The situation in the Ugandan highlands, as described here by Festus D.K. Bagoora, further demonstrates just how seriously lacking we are in institutional capacities to monitor the changes that human activities are imposing on the environment, let alone deal with them on the basis of a sustainable approach. Many Third World countries can only make the crudest kind of guesses about the extent of deterioration of their natural resources - and without this their ability to develop appropriate resource management policies is severely limited. In the following selection, Professor Bagoora, who is on the faculty of the Department of Geography, Makerere University, Kampala, Uganda, examines some of the implications of human-induced environmental degradation in the highland regions of his country. It is excerpted from his contribution to a special issue of the UNU journal, Mountain Research and Development which focused on the African highlands. - Editor
Human interference on steep slopes prompts accelerated erosion which, in time, may become catastrophic. Accelerated erosion, particularly on steep slopes, is a world-wide problem. Conservation and management of soil and water resources in the tropical highlands have become central issues to many planning problems concerned with natural and altered environments. In the highlands of Uganda, the problem has been dominated by denudation of vegetation and cultivation on extremely steep slopes, both of which are a response to increased population pressure on land.
The climate of much of the Ugandan highlands could be described as cool humid. Rainfall and humidity are particularly important parameters in determining erosion processes in the highlands. Storm intensities and duration are important measures of erosivity. Rainfall in the highlands is generally lighter and more prolonged than that which falls on the surrounding plateau regions. But occasionally heavy and erosive storms do occur, particularly after a dry season or the hottest period.
Such storms have become of great concern as they often cause serious erosion during periods of least vegetation cover when the peasant plots are freshly cultivated. Furthermore, the wet season peaks are associated with mass wasting in soils. Besides increasing rainfall incidence, high humidity means that, throughout the year, soils have a high water content which leads to high rates of runoff, soil erosion and mass wasting.
History of the Highlands
History indicates that - while some tribes in the mountain regions were forcefully driven there in fairly recent historical times by war-like tribes in the plains below - the inhabitants of major hilly districts have been resident there for over five centuries. Except in the dryer north-eastern highlands, the tribes of these highland environments are peasant cultivators practising a system of agriculture, typical of high, moist uplands, which is conditioned by both altitude and topography. This form of land use has done indelible damage to nature in some parts of the highlands.
Other than certain areas of the north-east, the highlands are inhabited by Bantu tribes. These contain the highest rural population densities of Uganda, with favourable climate and soils a major contributing factor. Population densities continue to intensify, and this has led to severe pressure on land and vegetation - and thus to serious environmental degradation in a naturally sensitive environment.
Increased population in areas of limited arable land has led to expansion of cultivation into rangelands or onto steeper slopes, which are normally areas of highest sensitivity to degradation. This causes destruction of vegetation, initially through shifting cultivation and later through a complex of other forms of vegetation denudation - such as the collection of firewood, cutting of building materials, charcoal burning, and indiscriminate bush burning.
Thus, all the highlands are experiencing destructive land-use practices and have, by implication, become endangered areas for future generations. As early as 1938, the Bakonjo tribe was described (by Wayland) as "experts in environmental destruction through their shifting cultivation." In Muhavura, cultivation is rapidly extending into the upper slopes as land shortage on the Kisoro plain intensifies. To the north-east, certain tribes are becoming more permanent settlers in the mountains, in contrast to their nomadic practices of the past. They have gone up with their animals to escape raids by the tribes on the plains below. The habit of bush burning and overgrazing has invaded the area and soon the already noted adverse consequences, such as intensive gullying on steep slopes, will reach alarming proportions.
Case Study: The South-West Highlands
To examine more scientifically the magnitude of the erosion risk in the densely populated Ugandan highlands, a case study focused on the Rukiga highlands in the south-western part of the country, near the border with Rwanda and Zaire. A carefully prepared questionnaire was administered to 53 randomly selected tax payers, from a district tax record, who were presumed to be responsible members of families and hence concerned about erosion.
The study indicated that conservation practices in the area have some antiquity, and were possibly initiated as soon as the farmers realized their predicament. By 1930, soil erosion and soil degradation had reached alarming proportions; by about 1935, the colonial government had become involved in enforcing conservation policies and practices.
Highland Areas of Uganda
A. above 3,000 m
B. 2,000-3,000 m
C. 1,500 -2,000 m
D. below 1,500 m
The south-western highlands were given special attention because they were considered to be at highest risk. The policies and practices that were adopted are similar to those normally adopted in other countries. They include legislation, continual expansion of forest reserves, and enforcement of tree planting on slopes. Also, the farmers were encouraged to use conservation techniques on their farms and public education about conservation was intensified.
Notable, however, was that the policies and practices were not based on any body of information data. The south-western highlands are said to have reached an advanced stage in the application of conservation measures by 1949. Unfortunately, this has since rapidly declined to the present dangerous situation of soil erosion, landslides and related phenomena. In one district alone, over 627 easily identifiable landslide scars were mapped, giving a density of 10 such scars per square kilometre. And these are only recent slide scars - if old scars masked by vegetation were to be included, the density would obviously be much higher.
Landslides were studied in relation to slope angle and land-use practices. Of a total of 27 landslides and debris slumps which were studied, 66.7 per cent originated in areas that have been cultivated, and 33.3 per cent in bushland and grassland. None were found in the woodlands of the particular study area.
Trees as Stabilizers
The results emphasize both the important role that tree vegetation plays in slope stabilization and the dangers of cultivation on steep slopes. Most landslides (over 90 per cent) were observed to occur during the peak rainy season of March-April. Probably landsliding is triggered by both gradual and sudden rises in pore water pressure caused by the heavy rains, which then reduce the shear strength of materials that begin to slide under the influence of gravity due to slope steepness.
Recommendations: Improve Data Base
Technical solutions to erosion problems are well known and have been outlined by various authors. However, to determine specific solutions suitable for local environments, further investigation must be taken on site. Conservation policies and practices once flourished in the highlands of Uganda, but later they declined and the area now faces rapid environmental deterioration. Moreover, there was no data base at that time, and hence it is difficult to evaluate the efficiency of these earlier policies for future replication.
Research is needed particularly on erosion plots on steep slopes. Studies also should be undertaken on rainfall intensities and erosivity in the highlands. Information on rainfall intensity/duration is non-existent and it will take time for such data to be compiled.
Some studies have indicated that storms in the highlands are less erosive than those on the plateau in and around the capital city, Kampala. But taking into account the nature of the topography in the highlands, the erosion risk is greater there than on the plateau. Moreover, the data we do have here were compiled at only a few stations and for only a few years; they should be used with caution.
Research is rather a long-term process. In the short term, the conservation policies of the past should be resumed promptly, and underwritten by reafforestation of badly damaged slopes. To discourage further deforestation, attempts should be made to provide alternative sources of fuel and building materials, such as hydropower, solar energy, biogas for energy, and tiles and bricks for building.
Finally, since population pressure is the major cause of soil erosion and landslides in the highlands, resettlement schemes should be set up to relocate people to the lower areas where population densities are lower. This is essentially a government undertaking, and it will require goodwill and significant financing. These early measures should be seen as temporary responses, however. Efforts need to be initiated so that the actual processes, both physical and social, can be more fully understood.
In conclusion, it must be re-emphasized that the settled highlands of Uganda are at a high risk of permanent damage by accelerated erosion. Urgent measures must be employed to alleviate this dangerous threat that continues to haunt the highland inhabitants.