Thorn forest

A thorn forest is a dense, scrublike vegetation characteristic of dry subtropical and warm temperate areas with a seasonal rainfall averaging 250 to 500 mm (9.8 to 19.7 in). This vegetation covers a large part of southwestern North America and southwestern Africa and smaller areas in Africa, South America, and Australia. In South America, thorn forest is sometimes called Caatinga, and consists primarily of small, thorny trees that shed their leaves seasonally. Trees typically do not exceed 10 metres (33 ft) in height, usually averaging between 7 and 8 metres (23 and 26 ft) tall. Thorn forest grades into savanna woodland as the rainfall increases and into desert as the climate becomes drier.

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Deserts and xeric shrublands

Deserts and xeric shrublands also called xerófila are a biome characterized by, relating to, or requiring only a small amount of moisture, usually defined as less than 250 mm of annual precipitation. It is the largest terrestrial biome, covering 19% of the earth's land surface area. They may be further characterized as hyperxerófila (very dry) and hypoxerófila (less dry).

Character of the biome

Biodiversity: Deserts and xeric shrublands may have a very diverse and rich flora. Reptile fauna may also be very diverse with pronounced local endemism in some regions.

Minimum resources: Many species track seasonally variable and patchy resources and require large natural landscapes to persist. Available water sources and riparian habitats are critical for the persistence of many species.

Poor soils: Because biomass productivity is low, the litter layer is almost nonexistent and the organic content of surface soil layers is very low. Also, evaporation tends to concentrate salts at the soil surface.