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Chapter 17Tropical Rain Forests as Old-Growth Forests In the context of this book, we may begin by making the general observation that many rain forests are par excellence old growth forests. They have the diagnostic characteristics mentioned in the companion chapter | Chapter 17 Tropical Rain Forests as Old-Growth Forests John Grace and Patrick Meir 17.1 Introduction In the context of this book we may begin by making the general observation that many rain forests are par excellence old growth forests. They have the diagnostic characteristics mentioned in the companion chapter Chap. 2 by Wirth et al. this volume including mixed ages and species and large amounts of standing and downed deadwood in all stages of decay. Some authors use the term virgin to describe them but generally they are not at all virgin having been colonised by indigenous people in former times using slash and burn agriculture and undergone re-growth for several hundreds of years Clark 1996 . This is known from artefacts and charcoal found in the soil Gomez-Pompa et al. 1987 . We also recognise old growth secondary forest which may have remarkably high biomass and much of the general appearance of undisturbed forest but lacks some of the biodiversity and the old and dead trees Brown and Lugo 1990 . The status of tropical rain forests is widely discussed in the literature. These forests occupy some 12 of the terrestrial surface they contain 55 of the biomass they are thought to hold over half of the global biodiversity. They occupy the warm and wet regions of the Earth occurring where the temperature of the coldest month is at least 18 C and where every month has 100 mm of rain or more. One can argue to some extent with these figures as the definition of tropical rain forest is not hard and fast see for example Richards 1952 Clark 1996 Whitmore 1998 . We may adopt one of the first definitions Schimper 1898 Evergreen hygrophilous in character at least 30 m tall and usually much more rich in thick stemmed lianas and in woody as well as herbaceous epiphytes. Tropical rain forests are disappearing at a rate that is also generally disputed but which is somewhere between 0.4 and 0.6 per year corresponding to 4 6 millions of hectares per year Achard et al. 2002 and .
