Saguaro National Park in Arizona, part of the Sonoran Desert

Physical Environment: Temperatures are variable, from below freezing at night to as much as 50°C in the day. Rainfall is less than 30 cm per year.  Location: Hot deserts are found around latitudes of 30° north and south. Prominent deserts include the Sahara of North Africa, the Kalahari of southern Africa, the Atacama of Chile, the Sonoran of northern Mexico and the southwest U.S., and the Simpson of Australia.  Plant Life: Three forms of plant life are adapted to deserts: annuals, succulents, and desert shrubs. Annuals circumvent drought by growing only when there is rain. Succulents, such as the saguaro cactus and other barrel cacti of the southwestern deserts, store water. Desert shrubs, such as the spraylike ocotillo, have short trunks, numerous branches, and small, thick leaves that can be shed in prolonged dry periods. In many plants, spines or volatile chemical compounds serve as a defence against water-seeking herbivores.  Animal Life: To conserve water, desert plants produce many small seeds, and animals that eat those seeds, such as ants, birds, and rodents, are common. Reptiles are numerous because high temperatures permit these ectothermic animals to maintain a warm body temperature. Lizards and snakes are important predators of seed-eating mammals.  Effects of Humans: Ambitious irrigation schemes and the prolific use of underground water have allowed humans to colonize deserts and grow crops there. However, salinization of soils is prevalent. Off-road vehicles can disturb the fragile desert communities.