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Dryland Systems Chapter 22 Dryland Systems Coordinating Lead Authors: Uriel Safriel, Zafar Adeel Lead Authors: David Niemeijer, Juan Puigdefabregas, Robin White, Rattan Lal, Mark Winslow, Juliane Ziedler, Stephen Prince, Emma Archer, Caroline King Contributing Authors: Barry Shapiro, Konrad Wessels, Thomas Nielsen, Boris Portnov, Inbal Reshef, Jillian Thonell, Esther Lachman, Douglas McNab Review Editors: Mohammed El-Kassas, Exequiel Ezcurra Main Messages . ............................................ 625 22.1 Introduction ........................................... 625 22.1.1 Definition and Subtypes of Dryland Systems 22.1.2 Ecosystems in Drylands 22.2 Ecosystem Services ..................................... 626 22.2.1 Supporting Services 22.2.2 Regulating Services 22.2.3 Provisioning Services 22.2.4 Cultural Services 22.2.5 Biodiversity and the Provision of Dryland Services 22.2.6 Integration: Services, Biodiversity, Livelihoods, and Aridity 22.3 Condition and Trends in Dryland Systems .................... 636 22.3.1 Land Degradation 22.3.2 Condition and Trends of Rangelands 22.3.3 Condition and Trends of Cultivated Drylands 22.3.4 Condition and Trends of Alternative Livelihoods 22.3.5 Condition and Trends of Dryland Biodiversity 22.4 Drivers of Change . .................................... 645 22.4.1 Conceptual Framework of Dryland Drivers: The Desertification Paradigm and Its Counterpart 22.4.2 Socioeconomic and Policy Drivers 22.4.3 Biophysical Indirect and Direct Drivers 22.5 Trade-offs, Synergies, and Interventions . ..................... 651 22.5.1 Traditional Dryland Livelihoods 22.5.2 Drylands and Other Systems 22.5.3 Climate Change and Carbon Sequestration 22.6 Human Well-being in Dryland Systems ....................... 653 22.6.1 Indicators of Human Well-being in Drylands 22.6.2 Human Well-being Components in Drylands 22.6.3 The Relative Dependence of Human Well-being on Ecosystems and Socioeconomic Drivers 22.6.4 Responses to Improve Human Well-being in Drylands 22.6.5 Services, Degradation, and Human Well-being REFERENCES .............................................. 656 623 ................. 11432$ CH22 10-11-05 15:04:45 PS PAGE 623 624 Ecosystems and Human Well-being: Current State and Trends BOXES 22.8 Land Use, Human and Livestock Populations, and Water 22.1 Forests in Drylands Availability across the Aridity Gradient 22.2 Desertification as Land Degradation 22.9 Dryland Degradation across the Aridity Gradient 22.3 Satellite Remote Sensing and Desertification 22.10 Transition of Grassland to Shrubland due to Stockbreeding in Semiarid Rangelands 22.4 How Much of the Dryland Is Degraded? 22.11 Desertification Paradigm and Counter-paradigm FIGURES 22.12 Impacts of Urbanization and Population Density on Income 22.1 Dryland Systems and Subtypes Levels in Drylands 22.2 Dryland Subtypes and Socioeconomic–Political Status 22.13 Comparison of Infant Mortality Rates and GNP per Capita 22.3 Population of Developing and Industrial Countries in Different across the MA Systems in Asia Dryland Subtypes and Population of Industrial Countries in 22.14 Human Well-being Statistics by Dryland Subtypes each Dryland Subtype as Percentage of Total Global Dryland Population TABLES 22.4 Global Area Covered by Dryland Subtypes and Their Broad 22.1 Statistical Profile of the Dryland System Biomes 22.2 Land Uses in Drylands 22.5 The Service of Climate Regulation in Drylands 22.3 Primary Production Expressed in NPP of Rangelands and 22.6 Number of Species of Flowering Plants in Selected Countries Wheat Yield in Croplands across the Aridity Gradient 22.4 Estimates of Dryland Carbon Reserves 22.7 Linkages between Services, Biodiversity, Livelihoods, and 22.5 Endangerment of Vertebrate Species in Three Dryland Dryland Subtypes Countries ................. 11432$ CH22 10-11-05 15:04:45 PS PAGE 624 Dryland Systems 625 Main Messages global drylands. Most likely the true level of degradation lies somewhere be- tween the 10% and 20% figures. To identify precisely where the problems Drylands cover about 41% of Earth’s land surface and are inhabited by occur and the true extent of degradation will require a more in-depth follow-up more than 2 billion people (about one third of world population). Drylands to these exploratory studies. are limited by soil moisture, the result of low rainfall and high evaporation, and show a gradient of increasing primary productivity, ranging from hyper-arid, Desertification, which by definition occurs only in drylands, causes ad- arid, and semiarid to dry subhumid areas. Deserts, grasslands, and woodlands verse impacts on non-dryland ecosystems (high certainty). Desertification are the natural expression of this gradient. has both direct and indirect impacts on non-dryland ecosystems and peoples. For example, dust storms resulting from wind soil erosion, driven by degrada- Dryland populations on average lag far behind the rest of the world on tion of the dryland vegetation cover, may affect people and ecosystems else- human well-being and development indicators (high certainty). The current where. Similarly, transport of sediments, pesticides, and nutrients from dryland socioeconomic condition of dryland peoples, about 90% of whom are in devel- agricultural activities affects coastal ecosystems. Droughts and loss of land oping countries, lags significantly behind that of people in other areas. productivity are considered predominant factors in the migration of people from drylands to other areas (medium certainty). Existing water shortages in drylands are projected to increase over time due to population increase, land cover change, and global climate Traditional and other current management practices contribute to the change. From 1960 to 2000, global use of fresh water (drylands included) sustainable use of ecosystem services. Many existing practices help pre- expanded at a mean rate of 25% per decade. The availability in drylands is vent desertification. These include enhanced and traditional water harvesting projected to decline further from the current average of 1,300 cubic meters per techniques, water storage and conservation measures, reuse of safe and person per year (in 2000), which is already below the threshold of 2,000 cubic treated wastewater for irrigation, afforestation for arresting soil erosion and meters required for minimum human well-being and sustainable development. improving ground water recharge, conservation of agrobiodiversity through di- This increased water stress will lead to reduced productivity of croplands and versification of crop patterns, and intensification of agriculture using technolo- availability of fresh water, resulting in further adverse impacts on human well- gies that do not increase pressure on dryland services. Policies that involve being in drylands. There is a high degree of certainty that global climate local participation and community institutions, improve access to transport and change, land use developments, and land cover changes will lead to an accel- market infrastructures, and enable land users to innovate are essential to the erated decline in water availability and biological production in drylands. success of these practices. Transformation of rangelands and other silvipastoral systems to culti- Alternative livelihoods have a lower impact on dryland ecosystem ser- vated croplands is leading to significant, persistent decrease in overall vices. These livelihoods still depend on the condition of drylands services but dryland plant productivity. Extreme reduction of rangeland vegetation cover rely less on vulnerable services and make use of the competitive advantages through grazing of forage and collection of fuelwood exposes the soil to ero- drylands can offer over other systems. They can include dryland aquaculture for sion. Transformation of rangelands to cultivated systems (approximately 15% production of high-value food and industrial compounds, controlled-environment of dryland grasslands, the most valuable dryland range, were converted be- agriculture (such as greenhouses) that requires relatively little land, and tourism- tween 1950 and 2000), in combination with inappropriate dryland irrigation and related activities. cultivation practices has led to soil salinization and erosion. These processes reduce the provision of water-related services, which affects the provision of Depending on the level of aridity, dryland biodiversity is relatively rich, many other significant dryland services and goods, culminating in persistent still relatively secure, and is critical for the provision of dryland services. reduction of primary production. Of 25 global ‘‘biodiversity hotspots’’ identified by Conservation International, 8 are in drylands. The proportion of drylands designated as protected areas is Among dryland subtypes, ecosystems and populations of semiarid areas close to the global average, but the proportion of dryland threatened species are the most vulnerable to loss of ecosystem services (medium certainty). is lower than average. At least 30% of the world’s cultivated plants originated Population density within drylands decreases with increasing aridity from 10 in drylands and have progenitors and relatives in these areas. A high species persons per square kilometer in the hyper-arid drylands to 71 persons in dry diversity of large mammals in semiarid drylands supports cultural services subhumid drylands. Conversely, the sensitivity of dryland ecosystems to (mainly tourism); a high functional diversity of invertebrate decomposers in arid human impacts that contribute to
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