Simulating the effects of climate change on tropical montane cloud forests

Tropical montane cloud forests are unique among terrestrial ecosystems in that they are strongly linked to regular cycles of cloud formation. We have explored changes in atmospheric parameters from global climate model simulations of the Last Glacial Maximum and for doubled atmospheric carbon dioxide concentration (2 x CO(2)) conditions which are associated with the height of this cloud formation, and hence the occurrence of intact cloud forests. These parameters include vertical profiles of absolute and relative humidity surfaces, as well as the warmth index(1), an empirical proxy of forest type. For the glacial simulations, the warmth index and absolute humidity suggest a downslope shift of cloud forests that agrees with the available palaeodata. For the 2 x CO(2) scenario, the relative humidity surface is shifted upwards by hundreds of metres during the winter dry season when these forests typically rely most on the moisture from cloud contact. At the same time, an increase in the warmth index implies increased evapo-transpiration. This combination of reduced cloud contact and increased evapo-transpiration could have serious conservation implications, given that these ecosystems typically harbour a high proportion of endemic species and are often situated on mountain tops or ridge lines.