Suchergebnisse

"Forests and Desertification" published on by Oxford University Press.

Abstract. Desertification is influenced by different factors that relate to climate, soil, topography, geology, vegetation, human pressure, and land and water management. The quantification of these factors into spatially explicit indicators and subsequent evaluation provides for a framework that allows us to identify areas currently at risk of desertification and to evaluate important contributing biophysical and socio-economic factors. Based on local knowledge of environmental contributing factors to the risk of desertification in the Binh Thuan Province of southeast Vietnam, a baseline 2010 map showed that 14.4 % of the area, mainly along the coast and in the northeast, is desertified with another 35.4 % at severe risk of desertification. The Vietnamese
Ministry of Natural Resource and Environment has defined the area with a ratio of rainfall to evapotranspiration smaller or equal to 0.65, which equals 1233 km2 or 15 % of the province, as desertified area, which corresponds well with the baseline 2010 map. The developed framework incorporates the important contributing factors and therefore allows for decision support in a "what if" structure and for the projection of potentially vulnerable areas under future scenarios. With projected climate change and population growth, the desertified area is expected to increase by 122 % (or 137 850 ha) towards 2050. The developed methodology can be extended to neighbouring provinces that experience similar sensitivities to desertification.

1. INTRODUCTION Geographers at the University of Lund have been active in research on desertification/ land degradation and environmental change monitoring of African drylands since the mid 1970'ies and of Asian drylands since the beginning of the 1990'ies. The results obtained so far do not confirm the concept of desertification as a mainly man made phenomena but indicate that the importance of climate variability and change has been underestimated (Helldén 1991). To learn about the importance of climatic fluctuations versus human impact on land degradation in arctic and sub-arctic environments, Iceland was selected for further studies. Iceland is not an arid, semi-arid or dry sub-humid region. Therefore the land degradation it is suffering cannot be called "desertification" in the strict sense as defined by the UN. On the other hand there is no doubt that land degradation has led to the creation of extensive desert like conditions in many areas of Iceland. In this sense, "desertification" is an Icelandic reality indicating the introduction and spread of desert like conditions in landscapes where there should not be any. 2. RESULTS There are few areas in Europe that have suffered such a severe and extensive land degradation as Iceland, leading to the creation of long lasting desert like conditions. It is estimated that when Iceland was settled, in 874 , at least 60% of the country was vegetated and that forests covered 15-25% of the country's area (Bergþórsson 1998, Þórarinsson 1961, Einarsson 1963, Þorsteinsson 1973). The vegetative cover is now about 27%. There is almost no forest (The Agricultural Ministry 1986, IGI/LMÍ 1993, Arnalds et al.1997). The scientific and political societies in Iceland often relate the land degradation problems to human over use of the rangelands, starting with the introduction of cattle and sheep rasing at the time of the settlement 874 AD. They consider overgrazing and overuse of the woodlands for fuelwood and charcoal production to be the most important processes opening and exposing the landscape for soil erosion with growing desert patches and deserts as a consequence. Most farmers, on the other hand, seem to believe that the desert patches and deserts are natural phenomena. The initiation and expansion of the phenomena is supposed to be related to climatic events possibly enhanced by the traditional winter grazing habit, no longer practiced. Our observations and preliminary results indicate that the importance of climate may have been underestimated as a possible and important cause of land degradation and desertification in Iceland. Cold and dry periods have probably favoured the development and expansion of desert patches and deserts. The Little Ice Age, especially during the second half of the last century, seems to have offered favourable conditions for frost processing and events of severe wind erosion. The second half of the last century is also characterized by an outstanding high population pressure and most likely a correspondingly high grazing pressure in the study area. Time series photos of erosion remnants development during a covering a 32 years period indicate that the erosion processes creating deserts may be supprisingly slow.

Iran has different climatic and geographical zones (mountainous and desert areas), mostly arid and semi-arid, which are suffering from land degradation. Desertification as a land degradation process in Iran is created by natural and anthropogenic driving forces. Meteorological drought is a major natural driving force of desertification and occurs due to the extended periods of low precipitation. Scarcity of water, as well as the excessive use of water resources, mainly for agriculture, creates negative water balances and changes in plant cover, and accelerates desertification. Despite various political measures having been taken in the past, desertification is still a serious environmental problem in many regions in Iran. In this study, drought and aridity indices derived from long-term temperature and precipitation data were used in order to show long-term drought occurrence in different climatic zones in Iran. The results indicated the occurrence of severe and extremely severe meteorological droughts in recent decades in the areas studied. Moreover, the De Martonne Aridity Index (IDM) and precipitation variability index (PVI) showed an ongoing negative trend on the basis of long-term data and the conducted regression analysis. Rapid population growth, soil salinization, and poor water resource management are also considered as the main anthropogenic drivers. The percentage of the rural population in Iran is decreasing and the urban area is growing fast. Since the 1970s, the usage of groundwater in Iran has increased around fourfold and the average annual decrease in the groundwater table has been around 0.51 m. The results of the study provide a better ex-post and ex-ante understanding of the occurrence of droughts as key driving forces of the desertification in Iran. Additionally, they can enable policymakers to prepare proper regional-based strategic planning in the future. Desertification cannot be stopped or managed completely, but could be mitigated by the adoption of some proposed sustainable land management strategies.

In the Indian context; contributed papers presented at the 22nd Conference of the Institute of Indian Geographers, and International Geographical Union Commission Meeting on Land Degradation and Desertification, held at the Dept. of Geography, Visva-Bharati University, on January 9-11, 2001

The word "desertification" was introduced in 1949 by the French scientist Aubreville in his report "Climats, forêts et désertification de l´Afrique tropicale". The concept, however, was discussed earlier by European and American scientists in terms of increased sand movements, desiccation, desert and Sahara encroachment and man made deserts. Desertification, at the beginning of last century, meant the spreading (expansion) of deserts or desert-like (non productive or very low productive) conditions from existing deserts into non-desert areas close to the desert margins. The symptoms of the phenomena were often related to sand movement and encroachment into oasis and desert margins. Aubreville also stated in 1949 that there are real deserts being born, under our very eyes, in the 700-1500 mm annual rainfall areas. One school favored the idea of a postglacial long term climate change (desiccation) as a major driving force causing desertification. Others stressed the importance of human impact. The human impact was expressed in terms of bad management of the natural resources including over cutting, overgrazing, over cultivation and misuse of water. Since then, different concepts of desertification have developed and been discussed over and over again by scientists, politicians and the international aid and development society. Important international events were UNCOD in Nairobi 1977, UNCED in Rio de Janeiro 1992 followed up by the UNCCD adopted in 1994 and entering into force in 1996. Mitigation approaches and control success or failure varies with concepts of causes and consequences. This is exemplified through a discussion of recent and relict desertification and mitigation cases in Europe, China and Africa. Conclusion: The causes, consequences and methods of control of desertification cannot be generalized but are site specific. Every site and case needs its own diagnosis, based on an integrated and systemic research approach, before the right cure can be identified and implemented.

"Desertification and Its Control in China" comprehensively discusses desertification from the views of formation, distribution, development and control models. This book truly elucidates basic theory and control models of desertification, especially the numerous results from research carried out for the UN Convention to Combat Desertification. This book will provide a theoretical and practical basis for ecological and environmental planning and design as well as guidelines for prevention/restoration for desertification projects. It will also provide practical examples."--Publisher description

Desertification offers a comprehensive overview of the subject and clearly emphasizes the link between local and global desertification processes and how past and current policy has affected arid environments and their populations. This text adequately applies the research undertaken during the last 15 years on the topic. Desertification has become increasingly politicized and there is a need to present and explain the facts from a global perspective. This book tackles the issues surrounding desertification in a number of ways from differing scales (local to global), processes (physical to hum