Simulating the effects of climate change on tropical montane cloud forests

Tropical montane cloud forests are unique among terrestrial ecosystems in t hat they are strongly linked to regular cycles of cloud formation. We have explored changes in atmospheric parameters from global climate model simula tions of the Last Glacial Maximum and for doubled atmospheric carbon dioxid e concentration (2 x CO2) conditions which are associated with the height o f this cloud formation, and hence the occurrence of intact cloud forests. T hese parameters include vertical profiles of absolute and relative humidity surfaces, as well as the warmth index(1), an empirical proxy of forest typ e. For the glacial simulations, the warmth index and absolute humidity sugg est a downslope shift of cloud forests that agrees with the available palae odata. For the 2 x CO2 scenario, the relative humidity surface is shifted u pwards by hundreds of metres during the winter dry season when these forest s typically rely most on the moisture from cloud contact. At the same time, an increase in the warmth index implies increased evapo-transpiration. Thi s combination of reduced cloud contact and increased evapo-transpiration co uld have serious conservation implications, given that these ecosystems typ ically harbour a high proportion of endemic species and are often situated on mountain tops or ridge lines.