Vulnerabilities of tropical forests to climate change: The significance of resident epiphytes

Predictions about the impacts of climate change on tropical forests require information on the relative vulnerabilities and roles of the biological components of these unusually complex systems. Central to the structure and function of any ecosystem - and the subject of this paper - is its flora, the energetic base for co-occurring heterocrophs. Much data indicate that arboreal flora (the epiphytes), those plants anchored in the forest canopy without access to the ground, occupy unusually climate-defined ecospace compared with co-occurring types such as the supporting trees. This report also describes how the epiphytes influence adjacent biota and whole-system processes, specifically those concerned with energetics, hydrology, and mineral cycling. Second, a mechanistic explanation for the exceptionally climate-sensitive nature of arboreal flora is provided. Finally, points one and two are used to make the case that arboreal flora represent a weak link in the integrity of certain types of forest, especially cloud forest and other types at lower elevations well known for their extraordinarily diverse biota. These plants, more than most, should provide early indications of floristic response to climate change throughout much of the tropics, but particularly in montane regions.