It may seem like drylands are just barren spaces, but they are actually ecosystems teeming with biodiversity.
The United Nations Environment Programme (UNEP) defines drylands according to an aridity index (AI), which is the ratio between average annual precipitation and potential evapotranspiration; drylands are lands with an AI of less than 0.65. Drylands are further divided, on the basis of AI, into hyper-arid lands, arid lands, semi-arid lands and dry sub-humid lands.
Drylands are found in most of the world’s biomes and climatic zones and constitute 41 percent of the global land area.
More than a quarter of the world’s forests are located in drylands. Trees are present on almost a third of the world’s dryland regions, equalling 1.1 billion hectares of forest, according to FAO’s Dryland Assessment. These trees and forests are hugely important for the planet. They provide habitats for biodiversity, protect land against wind erosion and desertification, provide shade for crops, animals and people, help water penetrate soils and contribute to soil fertility.
The rest of drylands aren’t just desert either: 25 percent of global drylands are grassland and 14 percent is cropland.
The soil environment is a principal component of the global carbon cycle where key interactions between biotic and abiotic components take place to regulate the flow of materials to and from the pedosphere, atmosphere and hydrosphere. There is general agreement that although soil is part of the climate change problem, it is also an integral part of the solution.
Carbon dioxide is removed from the atmosphere and converted to organic carbon through the process of photosynthesis. As organic carbon decomposes, it is converted back to carbon dioxide through the process of respiration. The quantity of organic carbon in soils is spatially and temporally variable, depending on the balance of inputs versus outputs. The inputs are due to the absorption of carbon dioxide from the atmosphere in the process of photosynthesis and its incorporation into the soil by the residues of plants and animals. Some of the dead plant matter is incorporated into the soil in humus, thereby enhancing the soil organic carbon pool. Decomposition of soil organic matter, releases carbon dioxide under aerobic conditions and methane under anaerobic conditions.
Drylands play an important role in both local and global climate regulation. It absorbs excess carbon from the atmosphere into the soil. Drylands account for about 46 percent of global carbon storage. Dryland soils contain 53% of global soil carbon storage, while dryland plants contain 14% of global biological carbon storage. Land reconstruction practices such as mulching, composting, fertilization, mixed planting and reforestation can increase soil carbon content and contribute directly to soil carbon sink.