Drylands (arid and semi-arid areas) cover approximately 40 per cent of the Earth's land surface. Although they are not as species-rich as more temperate or humid regions, they are home to many endemic species uniquely adapted to arid conditions. But much of this natural biodiversity is fragile, and held in a delicate balance that is easily affected by natural and human-induced environmental changes. This policy brief examines the current threats to biodiversity in dryland areas and suggests what we need to do to protect them. It concludes with a set of recommendations for policy makers working to conserve biodiversity in drylands.
Where are the world's drylands?
Drylands (arid and semi-arid areas) cover approximately 40 per cent of the Earth's land area and include diverse habitats such as deserts, forests and woodlands, savannas and steppes, wetlands, ponds, lakes and rivers. The most expansive areas of drylands can be found in Africa and Asia (see Figure 1).
|Figure 1. Global distribution of drylands |
The proportion of Africans and Asians living within drylands is also high, at about 42 per cent in each region — over 1.4 billion people in Asia, and 270 million people in Africa. Some of the highest population densities in drylands occur in sub-humid zones in China, India, the Middle East and West Africa. For example, in Burundi, Cape Verde, Egypt, The Gambia and Togo, there are over 100 people per square kilometre of dryland, yet the average population density in African drylands is only about 25 per square kilometre. 
Biodiversity in drylands
The total number of species in the world is estimated to be between 30 – 100 million, of which about 1.4 million have been formally described. Although the number of species in drylands is not well documented, it is generally accepted that species diversity is not as rich here as in more temperate or humid regions. But drylands are home to a relatively high number of endemic species — plants and animals uniquely adapted to the variable and extreme conditions of these areas.
Each such species has its own way of coping with variable water availability and temperature extremes. For example, some cacti have few or no leaves to reduce water loss through transpiration, while others have succulent tissues that store water. Other desert plants, such as some members of the lily family, remain dormant for long periods of time until sufficient water becomes available for growth and reproduction.
Animals in drylands are equally well adapted. Stenocara beetles, found in Namibia, do "headstands" on the ridges of sand dunes frequently blanketed by coastal fogs to catch droplets of water on their carapace. And kangaroo rats in the drylands of Central and North America obtain virtually all of their water by the oxidation of fats in dry seeds (metabolic water).
The International Union for the Conservation of Nature (IUCN) and the World Wildlife Fund (WWF) identify 234 Centres of Plant Diversity (CPD) worldwide, of which 42 are within drylands.  To qualify as a CPD, a mainland area must contain at least 1000 vascular plants over a diverse range of habitats, and at least 10 per cent of these must be endemic species. The plants and their gene pools must also be highly valued by indigenous and other people for their contributions to human subsistence, economic welfare, religious and cultural practices, and ecological importance.
Why conserving biodiversity in drylands is important
There is a growing recognition of the need to conserve dryland biodiversity not only for its own sake but also because biodiversity helps provide 'ecosystem services' on which people depend (see Box 1). For example, the WWF' has identified 138 regions around the world as "outstanding examples of the world's diverse ecosystems and priority targets for conservation actions", and of these, 31 are within drylands.  Similarly, the IUCN has identified about 1300 areas within drylands where the protection and maintenance of biodiversity is seen as essential.
Box 1. Ecosystem services in drylands
Processes through which the natural environment provides resources useful to people are known as 'ecosystem services' and are integral to life in drylands. These can be categorised into:
The importance of conserving dryland biodiversity is more apparent when we consider that half the approximately two billion people living in drylands are mired in poverty, and that all of them are directly and indirectly affected by the 'wellbeing' of local biodiversity.  For example, people living in drylands can only sustain their livestock if the biodiversity on which the animals depend is adequately protected. For some species, hardy natural fodder might need protection, while for others upstream watershed quality might need conserving to protect pasturelands downstream from flooding and erosion.
Another example of the need to protect dryland biodiversity stems from the fact that agricultural production in drylands is a significant fraction of the worldwide total. Further, people living in drylands make wide and wise use of traditional and endemic species for food, fibre and medicine. For example, they have domesticated indigenous trees for sustainable land use in Africa; sustainably used indigenous plants as forage for livestock and medicine for people in the dry northeast of Brazil; and both used and conserved mammals and other Andean wildlife in Bolivia, Chile, and Peru.
Why dryland biodiversity is under threat
The extreme conditions found in drylands mean that natural biodiversity is often fragile, easily affected by local human-induced habitat conversion, overgrazing or over-harvesting, the introduction of exotic species or changes in water availability, to name only a few sources of disruption. One result is the acceleration of soil erosion and nutrient loss leading to land degradation in major dryland areas. Although a precise estimate of land degradation in drylands is not known, major studies in the past 15 years suggest that up to 20 per cent of drylands are degraded (affecting over 250 million people), with a much larger fraction at future risk. [2,7,8]
Land degradation is further affected by demographic trends, a lack of adequate social and economic wellbeing, an absence of innovative technologies that enable people to live more sustainably, cultural factors and belief systems, and unresponsive institutions and policies. For example, the dry Seridó of northeast Brazil is becoming degraded through deforestation and forest fires set by local poor people to clear land, which result in uncontrolled withdrawal of water and the discharge of pollutants into reservoirs. 
Drylands are also under threat from irreversible human-induced global climate change. This threatens dryland biodiversity through changes in precipitation patterns and in local or regional temperatures, and through increases in the incidence of diseases like malaria or dengue fever. Unfortunately, scientific methods that can accurately predict these kinds of changes are limited.
Another major problem confronting drylands is the fact that the threats facing them are typically transboundary in nature, crossing local, national or regional jurisdictional lines as well as ecological boundaries like watersheds. For instance, some areas in India have adopted measures to protect water resources, only to see their water degraded by activities in other areas that also use the water but have not implemented water protection.  At the international level, protection of drylands that cross international boundaries requires agreement between respective countries. One example of where this has been achieved is the Vicuna Convention — signed by Argentina, Bolivia, Chile and Peru — which protects vicuñas in national parks and private lands in these countries.
Numerous policy recommendations exist for protecting drylands and their biodiversity — created by, for example, the United Nations Convention to Combat Desertification (UNCCD), the UN Convention on Biodiversity (CBD), the IUCN and the Millennium Ecosystem Assessment. All aim to improve drylands science and close the gap between science and policy. The following examples are representative of the types of recommendation needed to protect drylands biodiversity.
First, cross-disciplinary approaches are needed that include not only provisions for scientists with different disciplinary backgrounds to collaborate, but also for scientists and public policymakers to work together. Further, there is a need to include representative stakeholders in drylands biodiversity policy and decision making — for example, local indigenous peoples, farmers and pastoralists. This would enable local people to better understand and support scientific research, and ensure that it addresses their needs.
Fostering cross-disciplinary approaches is necessary because there are many complex links between biodiversity and the wellbeing of local populations. For example, in southern Africa, climate change is predicted to lead to a long-term drop in soil moisture, an associated loss of vegetation and stronger winds. This in turn will affect the stability of sand dunes, which are likely to become mobile, and the livelihoods of pastoral farmers, whose livestock depend on plants for grazing. 
Secondly, biodiversity needs to be brought into broader development strategies, as required by the CBD, to achieve sustainable development and poverty reduction. For example, there is no question that biophysical processes and natural phenomena are major factors in the degradation of drylands and biodiversity loss. But often, the underlying causes of the degradation and loss stem from conditions of poverty that force people to overuse fragile lands out of desperation, from unsustainable trade policies and subsidies, or from problematic land tenure systems that encourage the use of land for short-term gains at the expense of long-term sustainability. And, again, development strategies also must take into greater account the participation of the local population, especially women, as without their involvement conservation strategies are less effective.
Thirdly, most research supported by governments and funding institutions is carried out over a two to five-year period. But many biodiversity questions cannot be answered by this kind of short-term study, and more long-term research is needed if we are to fully understand the impact of biodiversity loss in drylands.
Last, scientists and policy makers need to develop their respective agendas in concert with international instruments such as the CBD, the UNCCD, and the United Nations Framework to Combat Climate Change.
John Lemons is professor of biology and environmental science in the Department of Environmental Studies at the University of New England in Maine, USA. (email@example.com)
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