The Causes and Progression of Desertification

Helmut Geist

• Publisher: Taylor & Francis
• Year: 2017
• Print ISBN: 9780754643234
• eBook ISBN: 9781351893299
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Geography
• Index: Geography

This book provides an examination into the causes and prospects of desertification through a systematic review of 132 sub national case studies. It uses a meta-analytical model to determine whether proximate causes and underlying driving forces fall into any patterns, to identify mediating factors, feedbacks, cross-scalar dynamics and typical pathways. It shows a limited set of recurrent core variables in varying combinations to drive desertification. Most prominent root causes are climatic factors, institutions, national policies, population growth and remote economic influences that lead to local cropland expansion, overgrazing and infrastructure extension, associated with desertification as a potential but not necessary outcome. Some factors are geographically robust; most of them are region and time specific.

Chapter 1

The Problem and Its Identification

Introduction

Studies located at the local- to national-scale demonstrate the importance and socio-ecological significance of desertification. Nonetheless, land-use/cover change in drylands remains poorly documented at the global scale, and causes are hardly understood (Puigdefábregas, 1995; Warren, 1996; Thomas, 1997; Reynolds and Stafford Smith, 2002; Lambin, Geist and Lepers, 2003). Consequently, the word ‘myth’ has been used (Forse, 1989; Helldén, 1991; Thomas and Middleton, 1994; Swift, 1996; Lambin, Turner, Geist, Agbola, Angelsen, Bruce, Coomes, Dirzo, Fischer, Folke, George, Homewood, Imbernon, Leemans, Li, Moran, Mortimore, Ramakrishnan, Richards, Skånes, Steffen, Stone, Svedin, Veldkamp, Vogel and Xu, 2001). The chapter presents what desertification is, why it is important, what studies have been carried out already, why there is still an information gap, and how a new approach like the one used in this book can contribute to fill the gap.

What is Desertification?

The process of desertification is thought to be widespread, such as tropical deforestation, but considerably less well documented and defined. More than one hundred formal definitions have been proposed so far, each emphasizing either an enormous breadth of the topic or focussing on unique issues, and most of them (often) displaying many particular spatial and temporal scales of interest, thus representing various disparate viewpoints in total. Identifying the differences of and distilling the commonalities from these definitions, Soulé (1991) and Reynolds (2001) state that desertification principally consists of three major components, i.e., the meteorological, ecological and human dimensions of desertification. The meteorological dimensions relate, for example, to drought, atmospheric dust, air temperature, elevated atmospheric CO₂, and intra- and interannual variability in precipitation. The ecological dimensions include, for example, nutrient cycling, plant growth, regeneration and mortality, microbial dynamics, plant cover, herbivory life cycles, and evapotranspiration. And, the socio-economic dimensions are often related to the loss of habitat, the fragmentation of crucial habitat, issues of overexploitation (such as overgrazing by domestic animals), the spread of exotic organisms (pests and weeds), air, soil and water pollution, and issues linked to climate change. Rather than proposing yet another definition, Reynolds and Stafford Smith (2002) select examples of definitions and classify them in terms of the emphasis given on the ecological, meteorological, and/or human or socioeconomic dimensions of the problem. For example, Graetz (1991) emphasizes mainly meteorological dimensions by stating that desertification means ‘the expansion of desert-like conditions and landscapes to areas where they should not occur climatically’. Others explore and define mainly the human dimensions of desertification, for example, in terms of ‘lower useful productivity’ for humans (Johnson, 1977), or by focussing on ‘land degradation … resulting from adverse human impact’ (Middleton and Thomas, 1997). Following Reynolds (2001), each of the components – be they ecological, meteorological, or human – is complex, difficult to predict, and highly interdependent, but a failure to recognize the simultaneous role of (and feedbacks between) these different components has led to many of the controversies and misconceptions alluded to previously.

Until today, the most authoritative definition of desertification remains that of the United Nations Convention to Combat Desertification (UNCCD): ‘land degradation in arid, semi-arid and dry sub-humid areas resulting from various factors, including climatic variations and human activities’ (UNEP, 1994). Thus, desertification refers to the degradation of land in dry zones. Conventionally, following the United Nations Conference on Desertification (UNCOD), held in Nairobi in 1977, desertification embraces ‘the diminution or destruction of the biological potential of the land [which] can lead ultimately to desert-like conditions’ (UNEP, 1977). According to the United Nations Environment Programme (UNEP), drylands climatically denote an area with rainfall up to 600 mm per year, and have a ratio of average annual precipitation to potential evapotranspiration (P/Etp; also referred to as the index of aridity) between 0.05 and 0.65. In other words, desertification is presumed to result in a reduction in the biological and, hence, economic potential of the land to support human populations, livestock, and wild herbivores in drylands of the world (Toulmin, 1998). While, by definition, desertification relates to drylands only, some scientists have expanded this definition to subsume the impoverishment of any terrestrial ecosystem which can be measured in reduced productivity of desirable plants, undesirable alterations in biomass and plant and fauna diversity, and accelerated erosion (Dregne, 1983; Dregne, Kassa and Rozanov, 1991; Watts, 2001; Dregne, 2002).

Desertification is about biophysical and socio-economic linkages, and how they affect human welfare (Blaikie and Brookfield, 1987; Puigdefábregas, 1995; Vogel and Smith, 2002; Mooney, Cropper and Reid, 2003; Turner, Kasperson, Matson, McCarthy, Corell, Christensen, Eckley, Kasperson, Luers, Martello, Polsky, Pulsipher and Schiller, 2003). It is a multidimensional issue, and several other concepts are important to this definition such as capability (or the quality of land to satisfy a particular use), sustainability (or the ability of the land to continue to produce over two generations, at least), vulnerability (or the exposure to hazards such as perturbations and stresses, and the sensitivity of the coupled human-environmental system experiencing hazards such as drought), resilience (or that quality of a resource that makes it sustainable or resistant to land degradation), and carrying capacity (or the number of people and animals the land can normally support without being significantly stressed). For example, responses and adaptation to land degradation are part of what desertification constitutes, or, in other words, the determinate political, economic and institutional capabilities of people in specific places at specific times (Watts and Bohle, 1993; Vogel, 1995). This implies that desertification is also about the social resilience of groups in dryland areas that are most vulnerable (Bohle, Downing, Field and Ibrahim, 1993; Vogel and Smith, 2002; Downing and Lüdeke, 2002).

The point has to be made here that different segments of society, or ‘stakeholders’, will view the issue with differing degrees of concern and interest (Stafford Smith and Reynolds, 2002). This poses a particular problem of how to research desertification as an outcome of dryland degradation. Reynolds, Stafford Smith and Lambin (2003) make the point that ‘what superficially appears straightforward may in fact be multifaceted, eschewing overly simplistic answers’, and Shi and Shao (2000) provide some exemplification of this in terms of soil and water losses from the Loess Plateau in China. Nonetheless, in terms of values implied, desertification is about endangerment in both social and environmental terms, and the term degradation needs to be clearly defined (Lohnert and Geist, 1999). A still very helpful example is the definition as put forward by Blaikie and Brookfield in their seminal work on land degradation and society (1987, p. 6).

[D]egradation is defined as a reduction in the capability of land to satisfy a particular use. If land is transferred from one system of production or use to another, say, from hunter-gathering to agriculture, or from agricultural to urban use, a different set of its intrinsic qualities become relevant and provide the physical basis of capability. Land may be more or less capable in the new context […] Socially, degradation must relate to capability.

In other words, desertification is not only about biogeophysical processes such as soil crusting and compaction, loss of soil structure and cohesion, gullying, sheet erosion, soil erosion by ablation, dune formation, local deposition in outwash fans, addition of sediment to water bodies, loss of productivity of croplands, pastures and woodlands, dust storms, increased atmospheric aerosol loadings, loss of surface roughness, increased albedo, decreased convection, reduced rainfall, and changed atmospheric conditions. By definition, desertification is about dryland ecology and capability. At the heart of desertification lies ecology, including the meteorological dimensions, grounded in the web of social relations that ties, for example, pastoral and/or farming households together, and links them to larger economic and political entities, namely, the market, the access to assets, land tenure, and the state (Swift, 1996; Turner, 2003). It has long been known that this ‘demands a careful study of local-level processes and demonstrates that environmental change needs to be carried out not in vague terms but at specific locations and among specific segments of … society’ (Watts, 1985).

Why is it Important?

Desertification is often seen as one of the most serious environmental problems confronting the world from at least the 1920s onwards. The process, however, is not confined to this period of time. Processes of desertification are of great antiquity, and the study of ancient desertification can be important per se, for example, to potentially derive generic principles for the co-evolution of human societies with their natural environments. Ancient or pre-historic desertification led to the collapse of civilizations and empires, and historic desertification led to the localized collapse of farming communities and population displacements. Clearly, the importance of these processes relate to ‘land degradation … resulting from various factors, including climatic variations and human activities’ (UNEP, 1994), and they do not include the formation of deserts per se, i.e., decoupled from human impacts such as the ‘browning of the Sahara’. The latter example of a purely biophysical process means the rapid conversion about 5,500 years ago of the Sahara, with a vegetation cover resembling that of a modern African savanna and carrying significant populations of large animals and humans, into its present desert condition. The ultimate cause was a small, subtle change in the Earth’s orbit, leading to a small change in the distribution of solar radiation on Earth’s surface, but triggering deleterious vegetation cover changes (Steffen, Sanderson, Tyson, Jäger, Matson, Moore, Oldfield, Richardson, Schellnhuber, Turner and Wasson, 2004).

Collapse of Ancient Societies

There are abundant examples of ancient societies which collapsed due to factors related to land use and dryland degradation (Runnels, 1995; Redman, 1999). For example, Bunney (1990) offers evidence of land degradation from early human history in the area surrounding Lake Patzcuaro in Mexico, and McAuliffe, Sundt, Valiente-Banuet, Casas and Viveros (2001) demonstrate how a very severe episode of erosion of cultivated uplands further south had turned, approximately 900 years ago, drainage basins of the Tehuacán Valley, the ‘cradle of maize’, into today’s degraded and impoverished areas. Olson (1981) examines clues from the collapse of ancient civilizations such as the Sardis in Turkey which suggest that over-exploitation of land resources played a significant role. In the following, two detailed examples are given of the pre-historic importance of desertification for human development and civilizations.

The ‘Fertile Crescent’ in Southwestern Asia, or today’s Near East, is probably the most intensively studied and best understood part of the globe as regards the rise and collapse of agricultural land use in what is now a fragile and widely degraded ecological dryland setting. The region appears to have been the earliest site for a whole string of developments, including animal as well as plant domestication and innovative food production, cities, states, writing, metallurgy, wheels, and what is termed civilization. However, the Sumerian civilization which exploited the Tigris and Euphrates river basin, for example, suffered the consequences of poor irrigation and salinity-induced desertification 6,000 years ago, and deforestation went hand in hand with the proliferation of desert-like conditions in Attica, which was noted by Plato some 2,500 years ago. Diamond (1999) provides some arguments on why domesticated plants and animals in Southwestern Asia and the eastern Mediterranean region gave the regions such a ‘potent head start’ with view upon modern world development, including the favourable Mediterranean climate, large stands of already highly productive wild ancestors of crops, etc. Turning to the ultimate causes why the region lost its enormous lead of thousands of years to late-starting Europe, proximate factors need to be addressed such as the development of a merchant class, capitalism, patent protection for inventions, failure to develop crushing taxation, tradition of critical empirical enquiry, etc.: why did they arise in Europe rather than Mesopotamia? Diamond (1999, pp. 410–11) identifies a westward shift of ‘civilization’, at the heart of which lies desertification. Actually, Europe received crops, livestock, technology, and writing systems from the Fertile Crescent, which then gradually eliminated itself as a major center of power and innovation.

After the rise of Fertile Crescent states in the fourth millennium B.C., the center of power initially remained in the Fertile Crescent (…). With the Greek conquest of all advanced societies from Greece east to India … in the late fourth century B.C., power finally made its first shift westward. It shifted farther west with Rome’s conquest of Greece in the second century B.C., and after the fall of the Roman Empire it eventually moved again, to western and northern Europe. (…) Today, the expressions ‘Fertile Crescent’ and ‘world leader in food production’ are absurd. Large areas of the former Fertile Crescent are now desert, semi-desert, steppe, or heavily eroded or salinized terrain unsuited for agriculture. (…) In ancient times, however, much of the Fertile Crescent and eastern Mediterranean region, including Greece, was covered with forest. (…) Its woodlands were cleared for agriculture, or cut to obtain construction timber, or burned as firewood or for manufacturing plaster. Because of low rainfall and hence low primary productivity (…), regrowth of vegetation could not keep pace with its destruction, especially in the presence of overgrazing by abundant goats. With the tree and grass cover removed, erosion proceeded and valleys silted up, while irrigation agriculture in the low-rainfall environment led to salt accumulation. These processes, which began in the Neolithic era, continued into modern times. (…) Thus, Fertile Crescent and eastern Mediterranean societies had the misfortune to arise in an ecologically fragile environment. They committed ecological suicide by destroying their own resource base.

Another prominent example of ancient (to historical) desertification outcomes linked to coupled human activities and climatic variations stem from the upland steppe plateaus of northern China (Sheehy, 1992; Zhou, Dodson, Head, Li, Hou, Lu, Donahue and Jull, 2002; Lin and Tang, 2002; Jiang, 2002). The zone has supported century, if not millennia-old nomadic or semi-nomadic grazing, and parts of it have now turned into the most desertified areas of China. During the Quaternary, the climate had changed several times, and the last episode of these climatic changes, the dry interval dating back to ca. 7,000 years before present, has been the current arid climate. Reinforcing climate predisposement was a change in the Quaternary geological environment, sometimes even called decisive for desertification in northern China. This had been the uplifting of the Tibet (Qinghai-Xizang) Plateau from 1,000 m (in the Pliocene) to the current 5,000 m, mainly during the past 10,000 years. The event strenghtened the Mongolian higher pressure zone and makes the climate drier and less rainy in northwest and north China. The uplifting impacted directly upon vegetation and surface soil cover, and thus became an immediate cause leading to present desertification. Mainly at locations in northwestern China such as the Ordos Plateau, pre-historic predisposement is reinforced by oscillating desert margins due to the coupled human-environmental impacts in ancient times. These had been both drastic climatic variations in the 11^th/1 3^th centuries, and again in the 17^th century, and destructive land uses under several dynasties, but especially in the Tang period (618–907 AD). What had previously been the Mu Us grasslands or meadows were located at the juncture of the Inner Mongolia, Shanxi and Ningxia provinces in northern China, which delineate the transitional zone between the sub-humid core areas of Chinese civilization, based on irrigated and sedentary agriculture, and the northern (semi)arid grasslands, best suited for nomadic and extensive pastoralism. Inappropriate land use in concomitance with biophysical changes has influenced the position of the desert margin. Desert ecosystems shifted southward by about three degrees of latitude to the present. Archaeological record proves that the natural vegetation of the semi-arid transitional zone was severely affected by the combined effects of human population increases, dry farming activities, forest clearance, and frequent warfares at around 3000–2000 ¹⁴C yr BP. Wind and water erosion became intense, and grassland ecology in some places changed to semi-desert or desert conditions, with mobile sand dunes starting to develop. The Xia Imperial Dynasty, for example, established in Shanxi Province in AD 413, was exterminated by wind-drift sand, and chaos was caused by subsequent war for 400 years. Nonetheless, at the beginning of the 5^th century AD, the natural environment at most locations had still fertile land with plenty of available freshwater and vast meadows with well-developed animal husbandry. Under the Tang Dynasty (established in AD 618), natural undergrowth was cleared, and grain was planted. Following frequent warfare during which forests and forage got burned (to destroy resources required by nomadic pastoralists) and natural grasslands trodden by warhorses, agricultural land was abandoned. Farmland, including irrigation ditches, became covered with sand transported by the winter monsoons. The western part of the Mu Us grasslands were reclaimed and cultivated during the Tang and the following Song dynasties (AD 960–1126) in succession, which again triggered desertification. By AD 822, high sand dunes had been created, with the Great Wall buried by sand in places at the middle of the 16^th century. Over this time period, alternations between livestock and grain farming caused the opening of more land for farming, more wood required for fuel, and more livestock for grazing. Further land reclamation was carried out during the Ming (AD 1368–1644) and Qing (AD 1661–1911) dynasties, exploiting what had been called ‘Mongolian uncultivated land’. The goals were to build a strong military and to boost the economy, which is why the Qing government strongly exploited the grasslands. It resulted in the complete desertification of an area previously called Mu Us meadow. It caused deserts to expand southeast towards the remaining grasslands, and made the active sand dunes move southwards. Within a period of 1,000 years, the desert had annexed land from the northwest to the southeast by as much as 150 km. The Mu Us meadow is now called Mu Us desert, the most seriously desertified area in China at present.

Dooming Prospects of Contemporary Desertification

Not the collapse of a whole society, but localized economic collapse, farm foreclosures and population displacements characterized a prolonged drought in the 1930s in the US-American Midwest. The historical case is typical for some features of contemporary desertification. First, it shows that land degradation relates to market systems which had not been characteristic for ancient societies (Polanyi, 1944). Second, it indicates that desertification occurs in some areas undergoing rapid land cover change (at changing times). Third, ‘hot spots’ appear to be spread over more than one hundred countries around the globe, thus constituting a truly global phenomenon (Lepers, Lambin, Janetos, DeFries, Achard, Ramankutty and Scholes, 2003). And, fourth, dryland degradation potentially triggers ‘crisis’ conditions. Henceforth, the interest in the historical ‘dust bowl’ case in the Great Plains of the United States of America, as described by Puigdefabregas (1995, p. 311).

[F]armers, encouraged by the high prices of cereals, after the shortage caused by World War I, plowed up large surfaces of marginal land and grasslands. By 1920, the cropping area on the southern plains was double that of 1910 (…), and during the widespread drought that arrived in the 1930s, the wind blew up enormous quantities of soil. This ‘dust bowl’ led to a mass exod...

Table of contents

• Cover
• Half Title
• Dedication
• Title Page
• Copyright Page
• Table of Contents
• List of Figures
• List of Tables
• Acknowledgements
• 1 The Problem and Its Identification
• 2 Research Design
• 3 Initial Conditions
• 4 Causes and System Properties
• 5 Syndromes and Process Rates
• 6 Pathways
• 7 Indicators
• 8 Discussion
• 9 Conclusions
• Bibliography
• Index