Constraints in Managing Soils for Sustainable Land Use in Drylands

B.G. Rozanov

(Moscow State University) United Nations Environment
Programme, PO Box 30552, Nairobi, Kenya

Chapter 10 of Soil Resilience and Sustainable Land Use by D.J. Greenland and I. Szabolcs, CAB INTERNATIONAL, 1994, pp.145-153.

reprinted and adapted with permission from CAB INTERNATIONAL

Introduction

Two key words determine the major issues in this volume - sustainability and resilience - recently both getting more and more fashionable, particularly in mass media and international political or semitechnical documents, with the result that they are ill-defined and grossly misused in many cases.

There are some inherited uncertainties attached to both terms. As the concept of sustainability does not imply any change in itself, either regressive (degradation of natural resources, civil strife) or progressive (soil improvement, socioeconomic development), but rather presupposes a quasistationary equilibrium, the introduction of the combined term sustainable development without clearly defining ecological or socioeconomic implications of such a combination, led to further confusion.

Therefore, one has to be very careful when using either term. For instance, for many experts sustainability means 'the same forever'. The socioeconomic consequence of such an understanding includes vigorous promotion of so-called 'traditional technologies' in the developing countries at a time of unprecedented rates of population growth when such technologies cannot either satisfy basic human needs or protect the environment. They were very good and appropriate a hundred years ago, but are absolutely useless now leaving their users in poverty and misery forever. It is just pure misuse of terminology and attached concepts, although, naturally, certain elements of the traditional technologies can be utilized with success. At the same time, resilience is not the synonym of stability, although the term is too often used in this way.

Common sense often helps in such difficult situations. Therefore, it is better to agree from the very beginning on what we are talking about and proceed with the necessary work, while time may provide more accurate definition. This is precisely what happened with the definition of desertification. In spite of a rather vague definition provided by the United Nations Conference on Desertification in 1977 (United Nations, 1977), the world was engaged in combating this menace, experiencing both success and failure for 14 years until a new, more precise and operational definition was adopted in 1990 (Odingo, 1990), then refined in 1991 (UNEP, 1991). Now we are going to witness intergovernmental negotiations on the global convention on desertification and the specific Chapter 12 of Agenda 21 adopted in June 1992 by the United Nations Conference on Environment and Development elaborates six problem areas within this concept, slightly redefined once more for the purpose (UNCED, 1992).

World Drylands

According to the latest concept adopted by UNEP for environmental assessment purposes, drylands are the temperate, warm or hot areas with a P/PET ratio [ratio of annual precipitation to potential evapotranspiration] less than 0.65 (UNEP, 1991, 1992). They are subdivided into hyperarid, arid, semiarid and dry subhumid territories (UNEP, 1991, 1992). [See the Global Humidity Index Map, especially its Legend for more details.]

The data show that 64% of the global drylands and 97% of hyperarid deserts are concentrated in Africa and Asia, although Australia is the driest continent in respect of the percentage of its total land surface.

There are three closely interrelated but very different phenomena that determine specific problems of the drylands and their use: aridity, drought and desertification/land degradation. These parts are distinguished not only by their physical nature but also by the major human strategies available to cope with them.

Aridity is a permanent climatic characteristic of an area that is determined and maintained by general global atmospheric circulation with certain local specifics imposed by topography; this characteristic is mainly manifested in the lack of atmospheric precipitation to support biological productivity. The human strategy for coping with aridity is:

1. to adapt living standards, behaviour and technology to corresponding climatic characteristics in accordance with the degree of aridity; and

2. to provide fresh-water supply for both human and animal consumption as well as for technological needs by either tapping underground aquifers or water transfers from outside.

Drought is a deficit or too-late arrival of atmospheric precipitation. It is usually defined in relation to the degree of probability as regards the 'normal' or more or less usual amount/date for a given locality within this or that aridity zone. Drought affects negatively local biological productivity (as well as consumer's water supply or electricity production by hydrostations) for a specific year or a season when it occurs. The human strategy towards drought includes:

1. accurate and reliable forecasting in time and space;

2. utilization of flexible production systems that incorporate diversified land use and specific technologies to be applied in time of drought; and

3. maintaining insurance reserves at various levels of social organizations to cope with disastrous effects when drought does occur.

Desertification is land degradation in arid, semiarid and dry subhumid areas resulting mainly from adverse human impact (UNEP, 1991). The main human strategy to combat desertification is adoption of ecologically appropriate land use and general land care in a favorable socioeconomic, legislative and political environment.

The above three phenomena and related human strategies to survive and develop constitute a unity, of which none of the parts can be treated separately in any programme designed to amend or mitigate either the environmental or the socioeconomic conditions of the drylands. These three characteristics of the drylands can be regarded as natural constraints to managing soils to achieve sustainable land use in these areas.

Present Status of World Drylands

By definition, all 6.1 bha (billion hectares) of the world's drylands are naturally subjected to aridity, to different degrees. However, there is no drought or desertification in 0.9 bha of hyperarid deserts like the Sahara. On the other hand, 5.2 bha of potentially productive drylands, 84% of the world's drylands, are prone to drought and desertification, usually in proportion to the degree of aridity, although with many important exceptions. It is not the arid but rather the semiarid areas which have the highest rate of land degradation mostly due to the differences in population pressure and patterns of land use.

It is estimated (UNEP, 1991) that about 3.6 bha, or 70% of potentially productive drylands, are currently threatened by the various forms of land degradation known as desertification.

1. Degradation of vegetation and sometimes soil in 3.3 bha or about 73% of the total area of dry rangelands, including all uncultivated non-forest lands and bushlands whether used at present as rangeland or not.

2. Decline in fertility and soil structure leading gradually to soil loss in 216 mha of rain-fed croplands, or nearly half of their total area in the drylands.

3. Degradation by waterlogging, salinization and/or alkalinization of 43 mha of irrigated croplands amounting to nearly 30% of the total area in the drylands.

As for the current human-induced soil degradation, it affects about 1 bha within the area of productive drylands, that is almost one-fifth of their total area (UNEP, 1992a). This includes mainly soil erosion by wind and water, and salinization of irrigated croplands. Soil erosion affects severely both rain-fed croplands and rangelands which are over-exploited and often left without protective plant cover. The situation is particularly serious on marginal lands in semiarid areas where cultivators encroach on the rangelands during occasional rainy years, and leave them bare during dry ones thus accelerating soil erosion. In places where the soil cover is thin enough, a few such cycles will result in hard rock coming to the surface thus transforming semidesertic dry steppe into true stony desert (Hammada, Gobi).

Drylands in almost 90 developing countries represent the largest global area of extreme and persistent poverty of the rural population. The poverty of people in these areas grows with the advance of desertification accentuated by a fast growth of population or alternatively, in some cases by migration. Degradation and ultimate loss of natural resources lead often to civil strife as evidenced by the present situation in the Horn of Africa.

People in the drylands, struggling daily with almost universal poverty, have no means to maintain or to improve their lands and have only one choice - to degrade them further. The sustainability of traditional technologies has not been able to match the present rate of population growth. Moreover, the growth of consumption demands now requires much greater norms of production in comparison with the not so distant past. In case of prolonged drought in certain areas, global food security is already in a precarious state. It will become much worse if desertification continues unabated.

Concept of Soil Resilience in Drylands

The above background characteristics of the world drylands seem to give little hope for appreciable benefit from soil resilience in these areas. However, this is not true. The most striking fact is that in spite of unprecedented growth of human pressure throughout the world drylands, both in qualitative and quantitative terms, the comparison of soil maps composed now and several decades ago, at least at a small scale, does not reveal a substantial soil change even in those areas where soil degradation processes were reported to be particularly active. This is a paradox which requires special investigation.

The most probable explanation of this situation can be found in the spatial pattern of soil degradation, particularly soil erosion. In the latter case, apparently, the major process is that of redistribution of the material within the catchment area without much outflow either by wind or water. Some of the material naturally, goes out of the area, but its major part is redistributed along the slope in the process of planation which could be active both in meso- and macroscales.

The present-day figure of soil loss in the world is estimated as 25.4 billion tonnes per year (UNEP, 1992b); this is the total removal of material from land surface to the ocean. Some time ago geologists estimated this at 24 billion tonnes, which is practically the same. On the basis of the total area of the global land surface, this is something like 1.9 t ha-l year-l as an average. This removal is certainly matched by the process of soil formation.

On the other hand, this is an average value which cannot actually be found anywhere. The actual rate of soil erosion varies from zero to more than 1000 tonnes per ha per year depending on a complex of local characteristics, the pattern of land use being one of the important ones. In certain areas there is accumulation of new material brought from the surrounding territories.

The second explanation of the above paradoxical situation can be connected with the methodology of assessing soil degradation and resilience. In estimating the degree of soil degradation and resilience in the drylands, and maybe elsewhere, the most common procedure is to measure how many tonnes of soil have been lost per hectare per year. In drylands this index has no meaningful value or practical importance: the most important point is what remains as a result of the erosion. Losses of the top 20 cm of some Aridisols on 50 m thick loess and of the same top 20 cm of some Luvisols, or Alfisols in African dry savanna have very different ultimate consequences. In the first case there will be no appreciable change in land capability, whereas in the second no capability will be left to support plant life whatsoever. The general concept of so-called allowable soil loss is total nonsense if the remaining soil is not considered. What is allowable in one area, may be considered catastrophic in another.

Furthermore, while considering the remaining posterosional soil we may come across very different situations determined by the nature of the exposed material. One such situation may be where the exposed material will be potentially more fertile than the removed topsoil. Naturally, the opposite case also occurs, and probably more often.

In any case it is no less important to assess the result of soil degradation than the process when soil resilience is estimated.

The need to define resilience introduces a new area of fundamental and adaptive research for the near future, in view of the growing human impact on the environment including soil. Till now we have not developed a full concept of soil resilience. At least, we do not know how to measure it or how to compare two soils in respect of this characteristic. Just qualitatively or conceptually it might be said that dryland soils appear more resilient than was previously thought.

Taking into account the above considerations, there is a need to distinguish very clearly between the resilience of land and that of soil. This distinction is particularly important for the drylands where all natural phenomena are accentuated by aridity. The resilience and relatively quick recuperation of dryland ecosystems after severe droughts is too often considered by ecologists in terms of a two-part subsystem of plants and animals completely forgetting the third component - soil. If the soil is not destroyed during the drought, as by wind erosion for example, the ecosystem might recover very quickly indeed, particularly in case of a decrease in human and animal pressure as a result of emigration or massive cattle loss (Olsson and Rapp, 1991). Otherwise the result may be quite different.

Constraints on Sustainable Land Use in Drylands

The constraints on sustainable land use in drylands originate from two sources. First, they are connected with the natural conditions of these areas as described above. Second, they are closely related to socioeconomic and political conditions, which are usually not very favourable in the developing countries in general and in the areas affected by desertification in particular.

The development of irrigated agriculture is limited by the availability of fresh water and by the use of backward technologies leading eventually to soil degradation. With 30% of the irrigated land already affected by degradation processes to some degree, any new irrigation project will bring about additional soil salinization because lands of lower and lower quality are being developed for irrigation. Where an irrigation project is constructed with modern sophisticated technology, including adequate water quality control and artificial drainage, the cost becomes so high that the investment is hardly profitable. Governments are providing certain subsidies for the development of irrigated agriculture, but that is not always paying under the existing trade climate.

As regards rain-fed agriculture and the pastoral use of extensive rangelands, they both have rather limited potential for large-scale production and both are very vulnerable to recurrent drought. At the same time for many developing countries affected by desertification, nomadic or seminomadic pastoralism or a combination of pastoralism with rain-fed agriculture are the only way of life and constitute the backbone of their economies.

It is the economic situation which constitutes the main constraint to managing soils for sustainable land use because any additional investment in the protection or rehabilitation of drylands should come from outside, whereas the investments have no immediate return and have long periods of gestation. Thus they are not attractive for the holders of capital. At present the major emphasis is on foreign aid, both bilateral and multilateral. However, governments, both local and national, do not always attach sufficient priority to land problems in their long lists of needs, and the major part of foreign aid goes to other areas.

Conclusions

The constraints on managing soils for sustainable land use in drylands are different in nature. Some are connected with the specificity of the natural conditions including soils, others with the prevailing socioeconomic conditions. Appropriate management of soils is the prerequisite of sustainable land use in the drylands, but this requires substantial investment which is not available from local sources and can only be achieved through international cooperation. Certain problems still require extensive research, e.g. soil resilience, particularly in view of the diversity of dryland soils in different ecological conditions. Another area of research in the drylands is the relationship between the processes of soil degradation and results in different ecological situations; to answer the question whether soil erosion is always harmful or whether it may be beneficial in certain cases depending on the nature of the soil parent material and soil formation. The above problems concerning the soils of drylands are recommended as priorities for fundamental and adaptive research by the appropriate scientific institutions.

References

UNCED (1992) AGENDA-21. United Nations, Rio de Janeiro.

UNEP (1991) Status of Desertification and Implementation of the United Nations Plan of Action to Combat Desertification UNEP, Nairobi.

UNEP (1992a) World Atlas of Desertification. Edward Arnold, London.

UNEP (1992b) Saving Our Planet: Challenges and Hopes. UNEP, Nairobi.

United Nations (1977) Desertification Its Causes and Consequences. Pergamon Press, Oxford.

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