IUCN considers drylands as tropical and temperate landscapes and regions with an aridity index value of less than 0.65, which includes the following dryland sub-types: dry sub-humid, semi-arid, arid, and hyperarid (deserts) (IUCN, 2008b). Such drylands constitute approximately 40% of the terrestrial surface of the planet, and can be found in both developing and developed countries. At least 30% of the world's cultivated plants originated in drylands, and drylands are home to 47% of endemic bird areas and 26% of protected areas worldwide.
IUCN has an inclusive approach to mosaic where temperature rather than water availability dryland landscapes, and so includes urban limits biological productivity. In addition, IUCN and wetland areas within dryland regions and also includes seasonal drylands in the scope of its landscapes. However, for the purposes of IUCN's drylands work, specifically grasslands where their programmes of work on drylands, Arctic and range and species composition are determined by Antarctic dry areas are excluded, as these are areas water scarcity.
Figure 18.1 Distribution of the world's drylands (MA, 2005a)
Biodiversity in drylands is well adapted to harsh conditions and drylands are significant locations for endemism around the world. Species' adaptive strategies range from the architectural wonder of termite mounds which insulate the colonies from extreme temperatures to the desert amphibians which burrow into the sand and remain dormant until rains come. Indeed, some of these strategies have been the source of important discoveries in support of improving human livelihoods. Nevertheless, with changing climate and increasing human demands on these dryland systems, the special biodiversity living here is under increasing threat.
Drylands are home to some of the most charismatic species, support high species endemism and comprise many unique ecosystems and biomes, including Mediterranean-type ecosystems, grasslands, savannahs, dry forest, coastal areas, deserts, fynbos and the succulent Karoo (the latter two being highly distinctive vegetation types unique to southern Africa) (Zeidler and Mulongoy, 2003; White et al., 2000; Bonkoungou and Niamir-Fuller, 2001). Furthermore, many other ecosystems, such as riparian or forest ecosystems are located within the drylands landscapes and are at risk from drylands degradation.
Functioning dryland ecosystems provide many ecosystem services including crops for food and medicines, forage for animals, genetic resources, water for both people and animals, and materials for housing and clothing. In addition, they can be important sources of income (e.g. tourism) or cultural and spiritual support. The potential value of some of these services can be expressed in terms of percentage of agricultural output in countries that are largely dryland. For example, agriculture accounts for more than 30% of GDP in Afghanistan, Kenya and Sudan. The dryland portions of India contribute 45% of the country's agricultural output. Chinese drylands are home to 78 million cashmere goats that supply 65–75% of the global market, and Mongolia generates 30% of GDP from dryland pastoralism.
Pastoralism, which is usually most profitable on lands marginal for crops, is an important source of livelihoods in drylands. Mobile herding allows better use of grazing land that is subject to variations in rainfall and temperature. Crop farming or sedentary herds of livestock do not have the flexibility to move when conditions are no longer suitable. However, some traditional practices support crop farming through tree planting and other mechanisms to support natural regeneration.
Dryland-adapted species tend to be ecologically resilient and able to cope with extremes of environment. Nevertheless, according to the Millennium Ecosystem Assessment (MA), 10–20% of drylands are being degraded, threatening billions of hectares of rangelands and croplands with subsequent impacts on the more than 2 billion people living in these ecosystems (2000 data).
Desertification is increasingly a topic of discussion beyond its “homeland” venue of the United Nations Convention to Combat Desertification (UNCCD). While desertification is an important issue for drylands, most drylands are not desertified. Desertification has been defined, through the UNCCD, as “land degradation in arid, semi-arid, and dry sub-humid lands”. In turn, that degradation is expressed as a persistent reduction of biological and economic productivity and can be measured by monitoring outputs of ecosystem services including crops and water supplies.
The causes of desertification include:
Social and economic policies
Forcing nomadic pastoralists to pursue sedentary cultivation lifestyles
Promoting or imposing land tenure practices that result in overexploitation of resources
Unsustainable land management practices, often resulting from the three previous points.
Desertification occurs on all continents except Antarctica and has particular impacts on the poor in drylands where they depend heavily on the ecosystem services that these systems provide.
While many impacts of desertification on drylands are local, there are also regional and global consequences. From an environmental perspective, loss of vegetation leads to soil loss, erosion, and downstream flooding. From the social perspective, people living in degraded drylands may be forced to migrate to other areas that are already crowded and unable to cope with increasing demands.
Other impacts of dryland degradation on associated lifestyles include:
Loss of indigenous (native) knowledge and traditional know-how;
Increased vulnerability of communities unable to adapt to variations and changes in conditions;
Marginalization of indigenous (native) peoples;
Conflicts in arid and semi-arid lands; and
Disappearance of traditional management institutions that have proven effective over many generations.
The loss of biodiversity, critically important in these challenging environments, is felt particularly keenly by dryland inhabitants. Dryland biodiversity, though, provides support not only for local inhabitants but is also the source of many services for wealthier parts of the world. Consider medicinal plants such as Harpagophytum sp., or Hoodia sp. used to treat common “Western” ailments such as arthritis and obesity. Without sound dryland management, solutions to today's and tomorrow's health problems could disappear before we discover them (Box 18.1).
Desertification is being driven by a suite of factors including water scarcity, intensive use of ecosystem services, and climate change. These factors are strongly linked as climate change will likely result in increasing water scarcity in many drylands with resulting decreases in services in spite of increasing demand. Such changes also tend to increase the risks of conflict.
Intensive use of ecosystem services, especially water
Continuing population growth and the consequent increase in food demand is likely to increase pressure to make land available for cultivation and could result in further degradation and conflict among ethnic groups. Dryland regions undergo cyclical episodes of water scarcity during which local people are more vulnerable to its effects, namely food shortages and health crises from lack of water.
Climate change impacts present a complex picture of possibilities for drylands. For some, more intense and extended drought could eliminate any productivity from a dryland landscape. For others, significant increases in precipitation (and in intensity in volume and temporal distribution) could transform drylands into more humid systems. This could potentially be beneficial but may also lead to conflicts between farmers and pastoralists.
Desertification contributes to climate change through soil and vegetation loss which decrease the land's carbon storage capacity. An estimated 300 million tonnes of carbon are lost to the atmosphere from drylands as a result of desertification each year (about 4% of the total global emissions from all sources combined) (MA, 2005a).
One of the most important efforts needed is increased understanding of drylands, factors involved and resulting vulnerability of local people. Decision makers and technicians charged with conservation and devising livelihood alternatives need appropriate knowledge on the potentials, limitations and ecological opportunities presented by arid and semi-arid lands and a better understanding of urban and external impacts on arid and semi-arid lands. In response, the Food and Agriculture Organization (FAO), along with many partners, has developed the Land Degradation Assessment of Drylands that includes mapping, indicators and country-level pilot studies to help increase our knowledge of drylands. The UNCCD and the World Meteorological Organization (WMO) are collaborating on a project to help with prevention, warning and monitoring of drought.
The value of drylands and dryland services also needs to be better understood. To date, drylands have been characterized by under-investment as potential opportunities are overlooked in favour of agricultural lands, tropical forests or marine ecosystems.
Water resource management
Integrated water resource management is a key means by which to prevent desertification by ensuring that land management policies are adapted to local traditions and needs. Such policies should support existing pastoralist lifestyles and maintenance of the traditional knowledge, avoiding unnecessary transition to more water-intensive cultivation. Dryland management involves water management and requires inter-sectoral cooperation to be effective. Reducing stress on dryland areas may sometimes require development and promotion of alternative livelihoods, including livelihoods in nearby non-dryland areas.
Restoration of degraded drylands
As with other degraded ecosystems, dryland restoration should be undertaken at a landscape scale, utilizing the principles of ecosystem approaches.
Drylands policy and governance
Dogmatic definitions of what a dryland is are not helpful in policy terms. In fact, the definition of drylands in the UNCCD differs from that in the Convention on Biological Diversity (CBD) with the former being more precise in terms of precipitation levels and the latter including a larger area through inclusion of specific vegetation types (Box 14.1). The result is a potential challenge for parties trying to implement drylands programmes of work in both conventions and this is a typical issue that underpins the need for harmonization across multilateral environmental agreements (MEAs).
However, no matter what the definition, the governance issues facing drylands management remain the same, namely:
Correcting the disenfranchisement of drylands people, including securing local land rights as well as related issues of self-determination, education, and health;
Decentralizing natural resource management including establishment of “local conventions” (community-based agreements) and enabling local people to be compensated for the nationally and globally-enjoyed benefits (through payments for ecosystem services provided by drylands); and
Strengthening the resilience of dryland residents, including pastoralists in drylands, through relevant policy frameworks and action.
As highlighted in earlier chapters, these governance issues will also need to bring in concerns relating to climate change (Chapter 5) and poverty reduction (Chapter 1).
Drylands are productive ecosystems supporting large numbers of people but these people are vulnerable to changing climates, markets and rights (Mortimore et al., 2008). Effectively managing drylands – and thereby preventing desertification – will be a major step towards poverty reduction and biodiversity conservation in a significant portion of our world.
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