Diversity and ecological domain of lichens
Among the terrestrial autotrophs of the world, lichens exhibit intri-guing morphological variation in miniature (Chapter4). In color they exhibit a fantastic array of orange, yellow, red, green, gray, brown, and black (Wirth1995;Brodoet al. 2001). Lichens vary in size from less than a mm*2 to long, pendulous forms that hang over 2 m from tree branches (Chapter4). Almost all lichens are perennials, although a few ephemerals (e.g.Vezdaea) are known. At the other extreme some lichens are estimated to survive well over 1000 years and may be useful in dating rock surfaces (Beschel1961; Section10.7). Linear growth varies from imperceptible to many millimeters in a year.
Lichens occur commonly as epiphytes on trees and other plants, and in some ecosystems epiphytic lichen biomass may exceed several hundred kg ha*- 1 (Coxson 1995). In addition, they frequently colonize bare soil, where they are an important component of cryptogamic soil crusts in arid and semi-arid land-scapes (Evans and Johansen1999; Belnap and Lange2003). Furthermore, lichens occur almost ubiquitously on rocks with the most obvious ones occurring as epiliths, either growing over the surface or embedded within the upper few millimeters. A few lichens even occur endolithically within the upper few millimeters of the rock, such as occurs in Antarctica (Friedmann1982). In the tropics and subtropics, some rapidly growing lichens even colonize the surface of leaves as epiphylls (Lu¨cking and Bernecker-Lu ¨cking 2002). Although most lichens are terrestrial, a few occur in freshwater streams (e.g. Peltigera hydro-thyria) and others occur in the marine intertidal zone (e.g. Lichinaspp. and the Verrucaria mauragroup).
Lichens occur in most terrestrial ecosystems of the world, but their bio-mass contribution varies from insignificant to being a major component of the whole ecosystem (Kershaw1985; Chapter 14). In many polar and subpolar ecosystems, lichens are the dominant autotrophs (Longton1988). In addition, lichens are conspicuous components of many alpine, coastal and forest ecosys-tems, such as the temperate rain forests of the southern hemisphere (Galloway 2007) and taiga of the northern hemisphere (Kershaw 1985). Because most lichens grow relatively slowly, their primary productivity contribution is fairly small in most ecosystems (Chapter10). On the other hand, the more rapidly growing species may increase their biomass by 20–40% in a year and these species may play an important role in the mineral cycling patterns of their ecosystems (Section12.10), particularly if cyanolichens are the dominant com-ponent (Chapter11)
Nash, Thomas H.,2008,Lichen Biology Second Edition,Cambridge : Cambridge University Press
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