Angrist
09-04-2002, 09:40 AM
Hey, can anyone help me get some info on desertification?? We're supposed to make some kind of report about it, but it's kinda hard to find informative sites. So does anyone of you where to find??
Xantar perhaps??
Thanks!! :D
Xantar
09-04-2002, 12:34 PM
Originally posted by Angrist
Xantar perhaps??
Sorry. I don't know anything about environmental science. sdtPikachu might know, but he seems to be MIA. :unsure:
I guess the best thing to do would be to look for a website on environmental issues (the kind that will give information about the global warming, air pollution etc.) because desertification is one of those issues.
It took me nearly a minute to find all this information, if people would just apply themselves:
de·sert·i·fi·ca·tion Pronunciation Key (d-zûrt-f-kshn)
n.
The transformation of arable or habitable land to desert, as by a change in climate or destructive land use.
Desertification is generally viewed as an advanced stage of land degradation. At the United Nations Conference on Desertification (UNCOD), desertification was defined as a "diminution or destruction of the biological potential of the land which can lead ultimately to desert-like conditions" (1978).
The processes of land degradation and desertification are not new. In "Prehistoric Farming Caused Devastating Soil Erosion," Bunney (1990) offers evidence of land degradation from early human history. Olson (1981) provides examples of ancient civilizations disrupted as a result of abusive land exploitation in "Archeology: Lessons on Future Soil Use." Only recently, however, have degradation processes commanded attention from policymakers at the regional and global levels.
The 1972 Stockholm Conference on the Human Environment was a milestone in concern over environmental preservation. In 1974, the United Nations called for global action on desertification with the passage of Resolution 3337 (XXIX) recommending a Conference on Desertification (UNCOD) in 1977. Appendix 1 of UNCOD (1978) includes the Plan of Action to Combat Desertification (PACD), consisting of 26 recommendations covering three main domains of intervention.
The United Nations Environment Programme and the International Soil Reference and Information Center (ISRIC) sponsored the Global Assessment of Soil Degradation (GLASOD), a baseline study that estimates global soil degradation. World Resources 1992-1993 includes a number of global maps from GLASOD and discusses causes of land degradation (World Resources Institute 1992).
Kyle W. Danish gives an analysis of the Desertification Convention of April 1995 and discusses the Convention's efforts to address the environmental degradation with a "bottom-up" approach. The article's analysis is based on international environmental legal norms.
The United Nations Conference on Environment and Development (UNCED) in 1992 specifically addressed land degradation and desertification in Chapter 12 of Agenda 21. Chapter 12 emphasizes the global nature of desertification and details recommendations for action at national, regional, and international levels. The implementation of adequate strategies requires further understanding of the following:
The Nature and Causes of Land Degradation and Desertification;
Human Factors of Land Degradation and Desertification;
The Status and Extent of Land Degradation and Desertification;
Costs Associated with Land Degradation and Desertification; and
Policies for Controlling Land Degradation and Desertification.
"Desertification" is defined in this web site, and in this research program as the reduction or spatial reorganization of net primary production in arid and semi-arid lands. As early as 1949, the scientist Aubreville noticed land degradation that seemed to be extending north into semi-arid and sub-humid regions of North Africa from the more arid zones of the Sahara (Aubreville, 1949). The term Aubreville coined for this process was "desertification". The problem had been observed in the Mediterranean World nearly two millennia before by the Roman senator Cicero who spoke of the destruction of the north African forests and their replacement by barren, desert-like areas. The devastating Sahel droughts of 1968-73 and the apparent accelerated southward advance of the Sahara Desert led to extensive international discussion of the problem and the formation of the United Nations Conference on Desertification (UNCOD).
At a meeting convened during 1977 in Nairobi, Kenya, UNCOD defined desertification as follows:
"Desertification is the diminution or destruction of the biological potential of land, and can lead ultimately to desert-like conditions. It is an aspect of the widespread deterioration of ecosystems, and has diminished or destroyed the biological potential, i.e. plant and animal production, for multiple use purposes at a time when increased productivity is needed to support growing populations in quest of development." (UNEP, 1978)
During the following years various agencies, scientific institutions and individual scientists found the above definition to be inadequate (UNEP, 1992). In response various groups developed their own definition, which, not unexpectedly, led to a significant amount of confusion. Additionally, cyclic oscillations of vegetation productivity related to climate fluctuations had been observed in satellite data, and there was a need to differentiate between desertification and these cyclic climatic oscillations (UNEP, 1992). In 1992 UNCOD settled upon the following definition of desertification:
"Desertification is land degradation in arid, semi-arid, and dry sub-humid areas resulting mainly from adverse human impact." (UNEP, 1992)
Perhaps the most significant aspect of this definition of desertification is its focus on "human impact." This differentiates the issue of desertification from simple climatic fluctuations such as drought, but it should be noted that drought can cause an exacerbation of damage derived from human activities. The definition of desertification offered by Mainguet (1994) states that desertification is "revealed by drought," but "caused by human activities." Nearly one-quarter of the vegetated land area of the Earth has been highly disturbed by human activity and an additional 28 percent has been moderately disturbed (World Resources Institute [WRI], 1993). This massive level of human disturbance suggests that there are large areas of the Earth's surface that have either been degraded through human activity or have a significant potential of being degraded through human activity.
Extent of the Problem
"In fact, so devastating seems the occupation of man that, with a few striking exceptions, a desert or near-desert condition is often associated with his long habitation of a region. Two major factors are believed to account for the growth of man-made deserts. In the first place, semi-arid to semi-humid regions proved the most favorable sites for the early development of human culture. Such areas, however, stand in a condition of delicate ecological balance between humid and true desert climates. In the second place, processes of soil erosion are accelerated by the exposure of soil surfaces hitherto protected by complete mantles of vegetation, whether grass or forest, by heavy grazing and cultivation. It is only within the past decade that experimental studies of these processes have been made. So enormous have been the differences in soil wastage and superficial runoff of rain waters from bared sloping lands, as compared with similar surfaces protected by a complete coverage of vegetation, that new light is thrown on the problem of the decadence of former civilizations." (Lowdermilk, 1935)
The World Resources Institute (1992) reports that "over the past 45 years, about 11 percent of the Earth’s vegetated soils became degraded to the point that their original biotic functions are damaged, and reclamation may be costly or in some cases impossible." UNCOD stated that as of 1992 desertification affects 70 percent of the world's drylands (3.6 billion hectares) or nearly one-fourth of the total land area of the planet (UNEP, 1992). However, UNCOD estimates have been questioned by workers such as Warren and Agnew (1988) who pointed out that about half of the arid area being used for the estimates is too arid for any form of agriculture. In fact, the UNEP (1992) definition of "rangeland" includes "non-agricultural, largely unoccupied drylands that are unused or used only occasionally by nomadic pastoralists," which suggests that the estimated area of degraded rangeland may be inflated, but, since the estimate of total rangeland would also be inflated, this may not change the fraction of usable arid lands that has been degraded. Even if the area of usable arid lands is only half of the value quoted by UNCOD, the region at risk represents one-sixth of the Earth's surface, and the reduced area of arid lands still included are those most used by humans.
The second important aspect of the extent of land degradation is the question of the potential for reversing the degradation. Nelson (1988) expressed the view that "the extent of desertification as an irreversible state has probably been exaggerated, although it is correct to classify it as a serious problem." Topsoil lost to erosion can usually be rebuilt given time, and the well-known process of biological succession shows that a forest ecosystem can replace an abandoned field in a few centuries. However, on the scale of people's need to use the land for sustenance, a few centuries is forever. Human effort can accelerate the regeneration of topsoil or ecosystems, shortening the time need for regeneration, but this may require considerable economic expense. In extreme cases of degradation where the clay fraction of the soil is nearly completely lost or invading flora becomes too firmly entrenched, natural recovery to the original ecosystem will not occur. Warren and Agnew (1988) point out lack of the knowledge needed to assess the resilience or recoverability of soils and plant communities.
Although the effects of land degradation have been less severe in the United States than they have been in areas such as the Sahel or Western Rajasthan (India), the United States itself has a great potential for the degradation of drylands. The historian Walter Prescott Webb once said of the Western United States:
"Draw a line anywhere from the region’s eastern boundary to the Pacific, stand on its mid-point and you will find yourself either in the desert or near it. If we do not understand the West it is because we perversely refuse to recognize this fact.. When the desert pokes a hot finger into the border regions, the people speak of a drought; when it pulls the finger back, they say 'the country is getting more seasonable.' At the heart of the desert there is no drought, there is only an occasional mitigation of dryness." (Webb, 1957)
The Western U.S. has been one of the most rapidly growing regions of the country over the last 100 years (Sheridan, 1981). Agricultural output from this region comprised more than 18 percent of the total agricultural output of the United States in 1977 (Sheridan, 1981).
That year the arid lands produced 66 percent of the nation's cotton, 39 percent of US barley, and 21 percent of the total wheat production (Sheridan, 1981). The annual rainfall in much of the West averages less than 51 cm (20 inches). This has long been considered to be below the threshold of successful agriculture without irrigation, and it was predicted that "these lands will maintain but a scanty population" (Powell, 1879). In order to support the large population and agricultural output of the West groundwater has been pumped out of the ground faster than it can be recharged, most of the region's rivers have been dammed to make water available on demand, and water has been transported over long distances from where it is more plentiful to where it is scarce (Sheridan, 1981). In 1893, John Wesley Powell told the International Irrigation Congress in Los Angeles, (Stegner, 1954) "you are piling up a heritage of conflict and litigation over water rights for there is not sufficient water to supply the land." This prophecy has been borne out as witnessed by the conflicts over water that have increased in intensity over the last few decades.
Given the large potential area of the United States in which degradation of drylands can occur and the unprecedented stresses due to its large population and vast agricultural output, it should not be a surprise to find that significant desertification has occurred in North America. Dregne (1983) reported that nearly 1.3 million square kilometers of North American drylands have been "severel" or "very severely" degraded. Over the last 100 years the Sonoran and Chihuahuan deserts have become perceptibly more barren, even though these areas have been deserts for a very long time (Sheridan, 1981). This problem is likely to get worse, not better: "The introduction of sprinkler irrigation systems, especially the center pivot systems, has enabled previously unsuitable rolling sandy lands to be cropped successfully. If and when those soils are abandoned, for reasons of economy or shortage of water, the United States will face an even greater wind erosion threat than it has had to cope with in the past" (Dregne 1983).
We can see the double-edged nature of the water problem here. The rate at which the water is being used in these arid regions around the world for irrigated agriculture is not sustainable, and for that reason the environmentally prudent thing would seem to be to severely curtail irrigation in these areas. When the irrigation is stopped, the area that had been under cultivation may become a source of blowing sand which further damages the environment of the drylands.
The Processes of Desertification
Another significant item in the current UNCOD definition of desertification listed above is the idea of "land degradation." UNCOD defined land degradation as follows:
"Degradation implies reduction of resource potential by one or a combination of processes acting on the land. These processes include water erosion, wind erosion and sedimentation by those agents, long-term reduction in the amount or diversity of natural vegetation, where relevant, and salinization and sodication." (UNEP, 1992)
Sheridan (1981) characterized the affliction of land degradation as having the following symptoms: declining groundwater tables, salinization of topsoil and water, reduction of surface waters, unnaturally high soil erosion, and the desolation of native vegetation. Dregne (1983) indicates the major processes of desertification in arid regions as: water erosion, wind erosion, salinization, waterlogging, and soil compaction. Additionally, the mechanical destruction of desert pavements and calcrete (caliche) makes the soil more vulnerable to erosion. Through these different processes, the land is made more barren, and it may become effectively like a desert, even without climate changes. Before continuing further to consider how to assess and monitor land degradation, we should look briefly at some of these processes.
The Challenge of Monitoring Desertification
"The image created has too often been of inexorably advancing sands, as opposed to more subtle, more complex, pulsating deteriorations, sometimes with reversals, but at least, with substantial periodic remissions, radiating out from centers of excessive population pressure." Nelson (1988)
Desertification is not, as sometimes envisioned, an invasion of non-desert areas from a desert core. Sheridan (1981) compares desertification to guerrilla warfare with no real "front line". Dregne (1983) describes desertification as a patch of land degraded through human abuse that then spreads outward if the abuse continues. A United Nations report (UNEP, 1978) describes the spread of desertification as follows: "These degraded patches, like a skin disease, link up to carry the process over extended areas." Mainguet (1994) clearly states, "The theory of the encroaching desert, which has now been scientifically rejected, is still a fixed idea in the minds of governments, donors, and journalists; this must change."
The extent of this “subtle and insidious process” (UNEP, 1978) of land degradation can be difficult to assess from observations on the ground. Ground observations may quickly show that soil is blowing from a farmer's field or the salinization is beginning in the soil; however, this single observation does not indicate the state of degradation a few miles away. Each site requires manpower-intensive biomass surveys and soil sampling. Furthermore, as indicated by the quotation from Nelson (1988) above, the desertification processes fluctuate over time, so repeated and ongoing observations are required to determine if progressive degradation is actually occurring and to track its progress. Warren and Agnew (1988) stated that one of the main problems in our understanding of land degradation was "the ignorance in establishing trends and speeds, because trends and speeds require sequential surveys." In addition, sequential surveys are of limited use if baselines for comparison are not established (Nelson, 1988; Rodenberg, 1991; Murray et al., 1994).
Remote sensing from satellites offers a potential means to survey all arid regions of the globe. However, remote sensing can not entirely supplant the use of ground observations as was widely believed in the 1970's and early 1980's (Mainguet, 1994). Still, satellite remote sensing can provide a powerful adjunct to ground observations by extending in time and space field observations made at a single point in a given region. Satellite remote sensing thus can monitor much larger areas than ground surveys and aid in targeting key ground observations. In this way, ground observation anchors satellite observations, with the satellite remote sensing effectively multiplying the value of the data acquired on the ground and identifying the specific localities where additional and repeat ground surveys are most needed.
Mainguet (1994) cites the importance of "remote sensing supported by verifications on the ground for a better perception of the extent and processes of degradation." Dregne and Tucker (1988) indicate that 30 to 40 years of observation by satellites and ground studies will be required to confidently determine any permanent changes in the boundaries of the Sahel.
sdtPikachu
09-12-2002, 10:07 PM
Makes sense to me :D
Long and short of desertifications is that if you chop down a rainforest (which have very fertile but very thin soil), it turns to desert. If you overfarm an arid area it turns to desert.
See, the environmentalists do have a point about many things kids.
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