The montane forest habitats of the Andes support exceptionally high biodiversity, with many species occupying narrow elevational ranges (e.g., Terborgh, 1977). These attributes, combined with the short migratory distances (often <30 km separates the lowlands from the upper forest line) allow montane forests to be extremely sensitive monitors of climatic change.

Andean montane forests, which we define to encompass temperate and montane rainforests within the tropical zone (after Huber and Riina, 1997), range from about 1,300 m up to about 3,300 km elevation. The mean annual temperature at the lower limit of the montane forest is about 20°C, with minima of c. 7°C (Colinvaux et al., 1997). Annual precipitation generally exceeds c. 1,000-1,200 mm, and ground-level cloud is frequent. Some caution is needed in grouping all montane forests together and assuming that they will respond similarly to a common forcing as species composition of montane forests varies significantly according to latitude, altitude, aspect, local precipitation, and soil type (Gentry, 1988). A further variable that must be included is that humans have occupied and modified these landscapes for millennia (Erickson 1999; Kolata et al., 2000), and there is uncertainty over the elevation of the upper forest limit in many parts of the Andes (Erickson, 1999; Wille et al., 2002).

In this chapter we will address some of the larger scale issues—for example, the migration of species in response to tectonic and climatic change, the stability of systems but instability of communities through time, and whether there is an out-of-phase climatic influence on southern and northern Andean sites during the last glacial maximum (LGM).

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