The potential negative impacts of global climate change on tropical montane cloud forests

Nearly every aspect of the cloud forest is affected by regular cloud immers ion, from the hydrological cycle to the species of plants and animals withi n the forest. Since the altitude band of cloud formation on tropical mounta ins is limited, the tropical montane cloud forest occurs in fragmented stri ps and has been likened to island archipelagoes. This isolation and uniquen ess promotes explosive speciation, exceptionally high endemism, and a great sensitivity to climate. Global climate change threatens all ecosystems thr ough temperature and rainfall changes, with a typical estimate for altitude shifts in the climatic optimum for mountain ecotones of hundreds of meters by the time of CO2 doubling. This alone suggests complete replacement of m any of the narrow altitude range cloud forests by lower altitude ecosystems , as well as the expulsion of peak residing cloud forests into extinction. However, the cloud forest will also be affected by other climate changes, i n particular changes in cloud formation. A number of global climate models suggest a reduction in low level cloudiness with the coming climate changes , and one site in particular, Monteverde, Costa Rica, appears to already be experiencing a reduction in cloud immersion. The coming climate changes appear very likely to upset the current dynamic equilibrium of the cloud forest. Results will include biodiversity loss, al titude shifts in species' ranges and subsequent community reshuffling, and possibly forest death. Difficulties for cloud forest species to survive in climate-induced migrations include no remaining location with a suitable cl imate, no pristine location to colonize, migration rates or establishment r ates that cannot keep up with climate change rates and new species interact ions. We review previous cloud forest species redistributions in the paleo- record in light of the coming changes. The characteristic epiphytes of the cloud forest play an important role in the light, hydrological and nutrient cycles of the cloud forest and are esp ecially sensitive to atmospheric climate change, especially humidity, as th e epiphytes can occupy incredibly small eco-niches from the canopy to crook s to trunks. Even slight shifts in climate can cause wilting or death to th e epiphyte community. Similarly, recent cloud forest animal redistributions , notably frog and lizard disappearances, may be driven by climate changes. Death of animals or epiphytes may have cascading effects on the cloud fore st web of life. Aside from changes in temperature, precipitation, and cloudiness, other cli mate changes may include increasing dry seasons, droughts, hurricanes and i ntense rain storms, all of which might increase damage to the cloud forest. Because cloud forest species occupy such small areas and tight ecological niches, they are not likely to colonize damaged regions. Fire, drought and plant invasions (especially non-native plants) are likely to increase the e ffects of any climate change damage in the cloud forest. As has frequently been suggested in the literature, all of the above factors combine to make the cloud forest a likely site for observing climate change effects in the near future. (C) 2001 Elsevier Science B.V. All rights reserved.