David Schellenberger Costa, Gerhard Zotz, Andreas Hemp, Michael Kleyer
Classifying species by their evolutionary history alone does not tell us how they may respond to global change. Rather, characteristics of plants and animals that can be related to environmental conditions are needed. These are called functional traits. Examples may be the thickness or water content of plant leaves (relating to survival in dry or cold conditions) or the diet of an animal (relating to survival under diminishing resources). Here, we collected functional traits of the plant species on the slopes of Mount Kilimanjaro, the highest free-standing mountain in the world. In the ecosystems covered, three distinct life forms co-occur: trees, understory plants, and epiphytes. The roots of epiphytes anchor these plants on the branches and trunks of their hosts, but in general, they are not parasites, i.e. they do not penetrate their host’s tissues. The growth conditions for the three plant life forms vary strongly due to differences in light, water, temperature, and nutrient access, among others. We expected this to be mirrored by their functional traits. Indeed, we found pronounced differences in functional traits including the chemical composition of leaves and their water content. We identified two distinct types of epiphytes: orchid-like species with thick leaves for water storage, and fern-like species with thin but leathery leaves that showed high resistance or even tolerance of desiccation. Overall, because traits vary so strongly between these groups, modelling approaches using traits need to take this into account to make realistic predictions in the face of climate change. In conservation contexts, this emphasizes the need to protect all plant life forms, because due to their distinct trait patterns, the groups have different ecological roles in the ecosystems.