II.

Stable Shrub Lands

Naturally stable shrub-land ecosystems cover large portions of the semiarid and arid parts of the earth. The most extensive shrub lands are found in a zone between 32° and 40° latitude north and south of the equator. These shrub lands include parts of semiarid southwestern North America, the Mediterranean region, central Chile, parts of Brazil, the Cape region of South Africa, and southern and southwestern Australia. For the most part the climate is characterized either by hot, dry summers and cool, moist winters or by pronounced wet and dry seasons. The shrub vegetation is dominated either by small-leafed evergreen shrubs able to survive fire and limited nutrients, or by shrubs that lose their leaves during the dry season. Among these shrub lands are the Mediterranean-type chaparral (see Chaparral), the caatinga of northeastern Brazil, and the mallee of Australia, which is dominated by low-growing eucalyptus. The cool, semiarid Great Basin of North America (see Desert) supports a northern desert shrub community dominated by sagebrush (Artemisia) and shad scale (Atriplex).

Other stable shrub communities result from the degradation of forest or grassland ecosystems due to overgrazing or deforestation. Among such shrub lands in the Mediterranean region are the garigue, the low, open shrub land of oak species resulting from the degradation of pine forests; and the maquis, a taller, more dense growth that replaced the cork-oak forest. In Scotland, heather moors resulted from the cutting of Scotch-pine forests.