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Global change | |||||||||
Desertification: identifying the symptoms to administer the cure | ||||||||||
The Mediterranean countries are under threat from a creeping desertification. Urgent policies are needed to protect and restore the most seriously affected areas. But what are the criteria to adopt as a basis for drawing up an objective list of priorities for action by the regional land use managers? It is in this area that the complex and detailed research carried out under the wide-ranging European project MEDALUS (Mediterranean Desertification and Land Use) is leading to a useful transfer of results by developing a set of desertification indicators. These are providing a precise diagnosis of the present state of the environment to formulate effective recovery strategies. MEDALUS was launched in 1991 and its third phase will end this year. During these eight and a half years, some 50 different research groups have been supported by the EU to investigate a huge range of problems relating to the physical causes and consequences of desertification, degradation and recovery in Mediterranean Europe. At field sites from Portugal to Greece, MEDALUS has monitored physical processes and properties in soil, water and vegetation. Simulation models have been developed to look at scenarios of further degradation and recovery, coupling these with models forecasting long-term climate change. In four regional target areas - Alentejo in Portugal, the Guadalentín basin in south-east Spain, the Agri basin in southern Italy and on the Greek island of Lesvos - the researchers have also combined physical monitoring and modelling with investigations of past and present land uses. Finally, they have been active on a Mediterranean-wide scale using remote sensing, general circulation models and large-scale physical process models.
A tool for land use management "A constant theme running through the project has been the reduction of the many processes and properties of the semi-arid landscape, which govern its sensitivity to change or indicate its state of degradation, into a handful of the most important ones, the desertification indicators," explains Dr Jane Brandt from King's College, London, project manager of MEDALUS. "The long-term intention in doing this, from the start of the project in 1991, has been to provide the land use managers with tools they might use for exploring the consequences of different land use changes on their environment." Underpinning all the work on indicators has been the field research programme. A total of 55 different parameters relating to atmospheric, vegetation and land use, soil and surface processes have been routinely monitored at the various sites. This work has been supported in two ways. First, there was the attempt to standardise field methods in these semi-arid, stony environments, by producing a manual of experimental protocols. This manual has since been used at all the field sites, thereby ensuring comparable results. A second handbook was also produced which discusses the identification of the critical thresholds of each of the parameters or processes and the derivation of the desertification indicators. "From this huge base of observations, which in some cases contains seven years of data, we have been able to identify a first set of those parameters which provide the best indicators together with their critical thresholds," says Jane Brandt. "For example, we can say that a soil depth of more than 15 cm is generally essential for the maintenance of perennial vegetation. Vegetation cover is another useful indicator and a cover of more than 40% will virtually eliminate the risk of soil erosion.
"This work does need to be taken further still. We are currently engaged in a major review of all the field protocols with a view to further refining the experimental techniques and removing those which have not been shown to be particularly useful. We also need to continue the work on the critical thresholds, because some have been shown to be variable across the Mediterranean region. For example, while a critical threshold for annual rainfall of 280 mm is a good indicator for desertification on Lesvos, it needs to be lower for the Guadalentín." Sub-regional approach The second area in which MEDALUS has contributed to desertification indicators is on a sub-regional scale thanks to pilot studies of the technique conducted in the four target areas. Here, a reduced set of parameters, derived from the field programme, were combined using a system of differential weighting to derive four quality indicators relating to soil, climate, vegetation and management. From these, the researchers produced maps of environmental degradation for the Agri basin, the Guadalentín basin, the Alentejo region and for Lesvos. "In the future, it is our hope to repeat this exercise, a number of times, in other areas of Portugal, Spain, Italy and Greece. In doing so we hope to find out which of the indicators we have developed can be universally applied across the Mediterranean region, and which need to be adapted to suit local conditions. Once this is done they can be used both for long-term monitoring of desertification (or recovery) at key research stations, or used in the management of affected areas."
Finally, MEDALUS has been active on a Mediterranean-wide scale. In this case, the project aimed to produce a regional degradation index for the whole Mediterranean basin. The index finally chosen is the potential for soil erosion, calculated from a physics-based simulation model with inputs of climate, vegetation cover, topography, and soils and geology. This has been used to identify areas with unacceptably high current rates of erosion and also areas with high sensitivity to increased erosion rates given potential changes in climate or land uses. Further research In the immediate future the work is likely to remain in the research domain because there are a number of elements that need addressing in order to improve its spatial resolution. There is also a need to look at the much closer integration of bio-physical and socio-economic indicators. "One way of doing this is to develop function performance indicators," says Jane Brandt. "All parts of the landscape perform a function, be it wheat production, soil and water conservation, or bio-diversity maintenance. The desertification of a landscape can be quantitatively measured in terms of its loss of function. For example, should erosion reduce the soil depth to such an extent that cereals can no longer be cultivated, its loss of function can be quantified. Similarly, the sensitivity to loss of function can be quantified. A functional approach also enables areas which are physically or socio-economically dissimilar to be compared."
Indicators of desertification have been the subject of much recent debate world-wide since the new United Nations Convention toCombat Desertification was ratified by more than a hundred countries and entered in force in 1996. "This really is an important starting point," concludes Dr Brandt. "The major limitation to current research on indicators has been the absence of a forum within which to work with managers and to test whether the tools work. However, things are now changing rapidly in the desertification world with the emergence of new bodies specifically charged with controlling Mediterranean degradation and restoring the ecosystem. The way is becoming open for the further transfer of research results into effective environmental management." Contact
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