1 Global and Neotropical Distribution and Diversity of Oak (genus Quercus) and Oak Forests

The genus Quercus is one of the most important clades of woody angiosperms in the northern hemisphere in terms of species diversity, ecological dominance, and economic value. Oaks are dominant members of a wide variety of habitats, including temperate deciduous forest, temperate and subtropical evergreen forest, subtropical and tropical savannah, subtropical woodland, oak-pine forest, oak-’piñon’-juniper woodlands, various kinds of ‘cloud forest’, tropical premontane forest, tropical montane forest, matorral (summer rain chaparral), and a variety of Mediterranean climate vegetations, including chaparral (French: maqui), oak woodland, and evergreen oak forest (Nixon 1993a, b, 1997b, 2002; Kappelle et al. 1995). Oaks also enter, and are important, along the margins of various other vegetation types, such as coniferous forests, prairies, tropical grasslands, desert and semi-desert scrublands, dry (deciduous) tropical forest, and in some evergreen tropical forests (Barbour and Billings 1999). Although many species of Quercus are exceptionally large, dominant overstory trees (Kappelle et al. 1995, Chaps. 8–11 and 14–17), perhaps an almost equal number of species are shrubs or small trees, particularly in drier habitats such as chaparral, in edaphically challenging environments, and in some higher elevation forests. Oaks also occur as ‘specialists’ in a diversity of edaphically distinct habitats, such as serpentine, sandy barrens, and swamps. However, in wetter forests oaks are often among the largest trees of the region, particularly when compared to other angiosperms. In the Americas, this is true both in the temperate deciduous forests of the eastern USA and in the evergreen oak forests of Mexico and Central America. Oaks also occur in the Himalayas and Southeast Asia (Indonesia). The economic importance of Quercus in the northern hemisphere is widely known.Various species are sources of high-quality lumber, and it is the