Dry and sub-humid lands, including arid and semi-arid regions, grasslands, savannahs, and Mediterranean landscapes, encompass approximately 47% of the Earth's terrestrial area, with the largest areas found in Australia, China, Russia, the United States, and Kazakhstan. There are six countries with at least 99% of their area classified as dry and sub-humid lands: Botswana, Burkina Faso, Iraq, Kazakhstan, the Republic of Moldova, and Turkmenistan.
Dry and sub-humid lands include many fragile environments that may warrant priority attention to avoid irreversible loss of biological diversity. Wetland areas in dry and sub-humid lands, for instance, are often of crucial importance in supporting migratory bird species. Dry and sub-humid lands also include important areas of extraordinary endemism, such as the Mediterranean Basin, which is home to more than 11,700 endemic plant species.
The biodiversity of dry and sub-humid lands is well adapted to the harsh conditions typified by inconsistent rainfall patterns, and, in many cases, high temperatures. The sociable weaver of southern Africa, for example builds communal nests which can weigh up to 1,000 kg in order to maximize insulation from extreme temperatures. Many species of desert toads burrow into the sand and lie dormant for months until the return of the rains.