Though drylands are less diverse than other ecosystems, they contain thousands of species that are highly adapted to the dryland environment yet often neglected in conservation efforts. Arid and semi-arid rangeland ecosystems have seasonal climatic extremes and unpredictable rainfall patterns, but dryland species have evolved to be highly resilient by recovering quickly from drought, fire and herbivore pressure. Desertification (also known as land degradation in drylands) is a worldwide phenomenon (see Section 8.4.2).
Dryland degradation has many causes, including human conflicts. Large amounts of waste, garbage and toxic material were dumped and burned in desert ecosystems due to the Islamic Republic of Iran-Iraq war (UNEP 2016f). Drought, overgrazing, overuse of groundwater and unsustainable agricultural practices impose additional pressures (O’Connor and Ford 2014; Southern Africa Development Community 2014), though the extent of human versus natural causes are often difficult to disentangle.
The degradation of semi-arid and arid landscapes reduces capacity in terms of freshwater supply and food production, decreases wild food availability, and presents a threat to emblematic species and genetic resources (Low ed. 2013). Desertification has a damaging effect on soil health and vegetation, leading to adverse impacts that cascade through the food chain (Assan, Caminade and Obeng 2009). Salinization, mostly due to unsustainable irrigation systems, irrigated areas with poor drainage and poor quality of irrigation water, is a major problem in arid and semi-arid regions (see Section 9.5.6). The almost complete desiccation of the Aral Sea has led to the creation of the Aral Kum desert, which has caused degradation of riparian forests, pastures and other vegetation cover (Kulmatov 2008).