Introduction: Regions of Mediterranean-type climate occur roughly between 30° and 40° latitude on the west coasts of continents, where offshore there are cold ocean currents. Each region in which the Mediterranean shrublands and woodlands occur is island-like in character and thus there is frequently a high degree of endemism. Comparative studies of the several regional expressions of this biome reveal interesting examples of convergent evolution in plant families and birds (but not among reptiles or small mammals) on the different continents. Climate: The Mediterranean Climate (Cs) is unique in that the wet season coincides with the low sun or winter period. Summers are dry. Total annual precipitation ranges between 15 and 40 inches per year. Temperatures are those of the subtropics moderated by maritime influence and fogs associated with the cold ocean currents. The result is a very limited, but predictable, growing season when there is both sufficient soil moisture and adequately warm temperatures. Many plants are adapted to Vegetation: Throughout the world, the Mediterranean biome is characterized by shrubs. In most regions these shrubs are evergreen and have small, leathery (sclerophyllous) leaves with thick cuticles. Sometimes the leaves are so reduced as to appear needle-like. Many typical members of the shrub flora are aromatic (for example, sage, rosemary, thyme, and oregano) and contain highly flammable oils. Mediterranean regions have long been impacted by humans especially through the use of fire and the grazing of livestock. The Mediterranean proper, we know from classical Greek literature, was formerly forested with live oaks, pines, cedars, wild carob and wild olive. The shrublands of California, likewise, are believed much more extensive today than before aboriginal burning and Spanish livestock grazing. Major regional expressions;
The Mediterranean proper–Europe, North Africa, and Asia Minor: around the Mediterranean Sea, which penetrates deeply into the Old World land masses, the biome reaches its maximum extent. Much of the formation is considered a subclimax developed on degraded and eroded soils and maintained in part by fire and goats. It is from this region that many culinary herbs associated with Italian cuisine originate. The shrublands are known locally as maquis. California: The chaparral (from the Spanish chapa or scrub oak) of southern California consists of two plant associations, the coastal sage and the foothills chaparral. The former is indicated by the presence of “soft” shrubs such as true sage (Salvia spp.). Inland, the latter is represented by a rich variety of “hard” woody shrubs that occurs in a mosaic reflecting fire history. A twenty-year cycle of fire maintains a subclimax of chamise (Adenostoma fasciculatum). In communities with less frequent or regular burns, chamise gives way to ceonothus, mountain mahogany, sumac, toyon, and manzanita. Dwarfed oaks and drought-resistant, closed-cone pines also occur. Adaptation or preadaptation to fire is important among various plant taxa: for example, • the flammable oils of chamise and other shrub species promote fire; • chamise sprouts from the roots after a burn;
• the resin coating the cones of closed-cone pines melts in a hot fire and allows the cones to open and disperse their seeds; • perennial forbs survive as underground bulbs and sprout quickly in response to the addition of nutrients to the soil after a burn; • the rosette shape of yuccas protects the inner growth bud from destruction in all but the hottest fires. Where fires have been prevented (and grazing also) for 50 years or more on Catalina and Santa Cruz islands (Channel Island group), an “elfin forest” of live oaks has developed. Some believe with even more prolonged suppression of fire, an oak savanna–perhaps the real climatic climax–would occur. California’s Mediterranean region is restricted mor or less to coastal areas by the...
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