The widespread fear that the Earth's deserts are spreading was reawakened by the major 1968–73 drought in Sahelian West Africa, Sudan, Ethiopia, and parts of Kenya. There appears, however, to be no firm evidence that a permanent desiccation of the arid zone is in progress. Instead, the evidence suggests that ‘desertification’—defined as the spread of desert surfaces, regardless of cause—results more immediately from faulty land-use practices and their interaction with prolonged natural drought episodes.

Desertification appears to be a process of degradation of grassland, scrub, or savanna, ecosystems under the impact of overstocking or excessive cultivation. During periods of desiccation there is widespread destruction of perennial vegetation, compaction of soil (especially near watering places), and deflation of fine materials (wind erosion).

Such surfaces are lighter-coloured than native vegetation, and reflect more sunlight. This may enhance atmospheric subsidence, and hence intensify drought. Loss of surface organic litter may also act as a positive feedback for drought.

Prediction of such episodes is at least some years away, but three possibilities exist for such prediction: use of cyclical variations, where present; time-lagged teleconnections; and general circulation modelling.

Reduced infiltration in some arid areas, combined with excessive withdrawals in others, have lowered both shallow alluvial and deep fossil ground-water tables—in some areas to the point at which stock water-supply can no longer be maintained.

Natural and semi-natural ecosystems in many parts of the world are in the most serious danger of being degraded or lost through Man's mistaking short-term economic gains under temporarily favourable conditions for long-term stability. This is particularly obvious in arid and semi-arid regions where ill-advised land-use methods have led to profound and often irreversible changes. Under the austere conditions prevailing in such regions, the dynamic ecological equilibrium is fragile: minor changes in the physical environment entail dramatic changes in plant and animal life. These circumstances lead easily to desertification. Due to overexploitation of natural resources by Man (especially overgrazing, and overcutting of shrubs) in North Africa, desertification has proceeded at a rate of more than 100 square kilometres per year. There is a great need to establish scientific bases for the conservation and rational use of the resources of natural and semi-natural ecosystems, especially in regions fringing the deserts where these resources continue to disappear regularly and all too rapidly.

The western Mediterranean desert of Egypt provides clear examples of such losses. As a result of the misuse of its resources, the region is producing at a rate that is probably far below its real potential. Agriculture (mainly barley cultivation) provides the livelihood for 74% of the population between Alexandria and Daba'a; this agriculture is either rain-fed (along most of the coastal strip), supplied by Nile and drainage-water mixed (Mariut Project, 500,000 feddan = 210,000 ha), or fed by irrigation and rainfall where Nile water is used as a supplementary source (Mariut Extension Project, 18,000 feddan). The most important land-use in terms of area, however, is animal husbandry (very largely sheep and goats, whose herding becomes more important and farming less important passing from the sea towards the interior). Actually there is overstocking, so that range vegetation is seriously depleted due to overgrazing and poor management.

Various land-use policies have been tried in the past decades with varying degrees of success, though fig and olive cultivations, which act within the framework of the natural ecosystem and with minimum human intervention, have a remarkable record of viability.

The Samdene Project (Systems Analysis of Mediterranean Desert Ecosystems of Northern Egypt) was conceived to bring together information on the Mediterranean desert ecosystems of northern Egypt. The Project involves the construction of predictive models simulating the major ecosystems of the region interms of energy flow and circulation of matter, and of spatial and temporal changes in plants and animals aswell as in soil features in relation to environmental variations.

So he preliminary results are already offered on soil moisture, vegetation, effects of fencing, phenology, litter production, and soil fauna.

Changes in land-use can have an important effect on rates of erosion and denudation. In order to avoid accelerating erosion rates, decision makers in land-use planning require adequate information on the contemporary geomorphological processes and hydrology of areas where modifications in the land-use pattern are envisaged. The first phase in the acquisition of the information is the reconnaissance survey, which shows where and how the erosional status of an area is likely to be affected, and also acts as a foundation on which to base more detailed work in the future.

The Solitude area is an active erosional system, dominated by mass movement and fluvial processes. The rate of removal of material is likely to be increased by modifications in land-use which, from other points of view, would be considered entirely suitable for the area. Therefore, if accelerated denudation is to be avoided, projects involving land-use changes should be implemented only by those having an adequate understanding of the mechanism of geomorphological processes operating in the area.

Rapid achievement of energy independence has become an urgent national goal in the United States. However public opinion, reinforced by general environmental legislation and specific energy-related legislation, demands that the development of energy alternatives will not be at the expense of the environment. One area of strong concern regards landscape restoration.

This subject is highly controversial, and responsibility for research and regulation is currently scattered among a number of Federal and state agencies and bureaux. Examination at the programme level indicates that many groups are working in closely related scientific areas. The Energy Research and Development Administration (ERDA) is making a detailed project and task analysis to determine whether true duplication rather than complementation of effort exists. From this analysis and a subsequent interagency effort, an integrated and fully coordinated restoration research programme can be designed. The size of this programme will need to be commensurate with the size of the problem. Hence, reclamation activities must be geared to the great diversity of ecological systems that are present in the United States, with due consideration of the full array of alternative energy-development possibilities.

Clearly, energy development involves a process of trade-offs. Thus it is the responsibility of ERDA to ensure that energy options, proposed for the future, are accompanied by a complete assessment of environmental costs—so that energy-environmental tradeoff decisions can be made early in the development of the technology, and can be based on a solid foundation of ecological knowledge. In order to carry out this mandate we shall need to establish sites for longterm energy impact research (in every major ecosystem), help design a coherent national land-reclamation programme, support an adequate amount of basic and imaginative applied research, and develop public demonstration areas where citizens, industrialists, and professional specialists, can observe longterm results of energy-environmental effects.

Prompt action demands that we capitalize upon past studies and develop a programme to learn as rapidly as possible about basic reclamation processes, so as to provide the best available knowledge to society's decision-makers. Follow-on studies must be conducted to validate and improve our reclamation predictions and management activities. The Argonne National Laboratory, which will provide a central focus for the ERDA land-reclamation research, will gather and collate all pertinent data, so that models and generic statements regarding reclamation techniques can be developed to guide us.

In order to have an adequate supply of clean, safe, and environmentally accepted energy, we will need the full cooperation of all. Only by moving together can we ensure for posterity an environmental heritage as rich as that which we ourselves have enjoyed.

Arab oil money is currently being invested in agricultural development of the Sudan. To halt desert expansion and to develop arid regions are different problems, however. The former could not be achieved without stronger political and sociological measures than would be acceptable to the inhabitants. The latter may be financially rewarding, but agricultural schemes may be attended by considerable risks that are often overlooked until too late.

It is argued that small improvements may prove to be sounder investments than grandiose schemes, and that the latter, if adopted, should always be tested by experimental pilot projects prior to any wide implementation.

Large areas of Papua New Guinea are covered by tropical rain-forest, but national and local pressures for development are causing increasing areas to be cleared for agriculture or logged for timber. Despite concern by conservation-minded land managers, a number of constraints make planning for the rational use of these resources rather difficult.

The problems encountered are mainly sociological rather than ecological. Thus while landowners are willing or eager to sell the rights to harvest the timber on their land, they are unwilling to commit the land to any long-term land-use, whether this be as managed forest, national park, or wildlife reserve. The problem is compounded by the complicated system of land tenure and the fact that several language-groups may commonly be found within even a small area.

The Gogol Timber Project at Madang illustrates some of these difficulties and the attempts that are being made to overcome them.

The suggestion, made in two earlier papers, that the use of a standard discount rate is not appropriate the planning of the environment, is considered further. It is concluded that the approach suggested in those papers may be of general validity in investment and cost/benefit decisions of all types. This approach involves an assessment of risks, together with an assessment of the expected ratio of investment: income.

Wetlands represent significant reservoirs of wildlife and natural diversity, in addition to any role which they may play in underpinning the productivity of river, estuarine, and offshore, fisheries. Various campaigns have been mounted to publicize their value and plight, but it is argued that the pressures for development and economic growth are often such that the ecological issues are obscured.

The biology of the estuarine environment is discussed as a first step to evaluating the impact of pollution and land-use policies. The impacts of urban, agricultural, and recreational, uses of wetland areas are reviewed, with particular reference to wetland ecosystems in Third World countries.

The paper concludes by arguing that the estuarine environment needs to be considered as a single ecosystem, and that an understanding of the carrying capacity of a given environment is a necessary precondition for sound management policies. The destruction of natural resources in the process of development planning effectively inflates the costs of that development, emphasizing the need for an ecological basis for planning decisions. The importance of experiment in evaluating alternative land-use options (such as intensive fish-farming) is stressed, and a simple model for ecologically sound development is proposed which could apply to Lake Manzala, in the Arab Republic of Egypt's Northern Wetlands.

Very precise measurements of the movement of coarse-textured, unconsolidated materials may be meaningless. Therefore the study of individual processes operating on footpaths may require a different approach. However, for identification of changes of reasonable dimensions, methods such as those described above are inexpensive, quick, and require no technical expertise. It may be argued that, for path management, erosion that is too limited to be measured by these methods is too limited to be a problem. It can certainly be argued that the problem of spatial correlation implies a large number of measurements. What is lost in lack of precision may be more than compensated for by the gain in data from the larger area and wider variation in site-types that it is possible to monitor with such simple techniques.

To monitor the effects of recreation in mountain areas, it is desirable to be able to measure any change in path-state and relate this to recreation factors at different seasons and under different sit; -conditions. Three methods of measurement have been considered in this paper, corresponding to three time-scales. Aerial photography has been used to demonstrate trends over the long term, and has proved adequate to differentiate between path sections with differing resistance to erosion.

Short-term measurement has been carried out relative to known fixed positions. Two methods are suggested. One is less precise, but simple and widely applicable, and can be used for measurement intervals of six months to one year. The other is more detailed and can be used for measurement intervals of a few days, but is limited in its application by practical considerations.

It is suggested that simple techniques used at a large number of different types of site may be more effective than detailed measurements at a few sites.