The Mediterranean Basin represents the largest Mediterranean-type ecosystem in the world, covering a complex landscape with great topographic and climatic heterogeneity. The total area of the region is about 2.3 x 103 square kilometers, or nearly 10 times the size of any other MTE region. The region includes more than 20 nations arrayed on both sides of the Mediterranean Sea. While coastal areas are extensive due to the presence of numerous archipelagos and islands, much of this area consists of mountainous terrain with many areas above 2000 m elevation and peaks as high as 4500 m.
The geographic position of the Mediterranean Basin is an important factor in understanding the biodiversity of this region. Lying at the juncture of three continental landmasses, its geologic history includes dynamic changes associated with plate tectonics, mountain uplift, and active volcanism. Strong climatic shifts that took place during the Plio-Pleistocene period, most notably major glacial episodes, resulted in the telescoping of many communities into the Mediterranean Basin and provided opportunities for geographic isolation and speciation. In contrast to the world’s other Mediterranean-type ecosystems, the majority of the Mediterranean Basin is underlain by limestone. However, local areas of volcanic or siliceous rocks are present.
The climatic characteristics of the Mediterranean Basin are often used to define this region, but the range of dominant and widespread woody species such as holm oak (Quercus ilex) and olive (Olea europea) also are used as bioindicators of its borders. To the north, the region grades into more mesic areas with summer or year-round patterns of rainfall. To the south, the Mediterranean region intergrades with the winter rainfall desert of the northern Sahara. Climates of the Mediterranean Basin are notable for their high interannual variation in both rainfall and temperature extremes.
The large area of the Mediterranean Basin, coupled with its topographic and climatic heterogeneity, makes for complex assemblages of vegetation types. There are extensive woodlands dominated by both evergreen and deciduous species of oak, but also evergreen sclerophyllous shrublands of many forms. The shrublands are often differentiated into types classified by height. Tall sclerophyllous shrublands that may include small evergreen trees are termed maquis. Several species of Mediterranean pine may be present in maquis. Medium-height shrubland, generally occurring on calcareous substrates, is termed garrigue. The low, semiarid evergreen shrublands found in the eastern Mediterranean Basin are commonly termed phrygana in Greece and batha in Israel.
The conversion of natural areas to agriculture and urban development since prehistoric times has had a strong affect on community structure and diversity in the region.