THE PAST AND FUTURE OF AFRICAN FORESTS: INFERENCES FROM MODELS AND LAKE MUDS

Climate and land-use change will have a dramatic impact on future ecosystems through alterations to species ranges and community composition. In order to develop conservation strategies, correlative species distribution models are often created to assess risk to individual species. These models are based on the assumption of climatic equilibrium, such that the modern range is representative of the full range of conditions under which species could thrive. However, the paleoecological record illustrates numerous examples of disequilibrium amongst both common and rare species today, and recent studies suggest that many species could occur in much broader climatic settings than previously thought.

Montane ecosystems are thought to be at disproportionate risk due to species’ temperature sensitivity and restricted geographic ranges. However, in the Afrotropics, the paleo-record suggests large geographic range changes over the late Pleistocene in which montane forest taxa expanded into the lowlands, suggesting a possible tolerance to warm temperatures. In order to evaluate climatic tolerances of afromontane ecosystems, we integrate paleoecological and paleoclimatic data from throughout tropical Africa from the mid-Holocene and Last Glacial Maximum in order to compare climate conditions in which species are currently found with climate in which these species were found in the paleo-record.

We show that many afromontane trees have occupied warmer climates in the past, which suggests that current low-elevation boundaries are not set by climate. Interestingly, the species with largest disequilibrium between paleo and modern distributions are those whose modern distributions show the least sensitivity to temperature. Mapping of species’ potential ranges based on modern and paleo-distributions clearly shows that suitable climate conditions exist today in the East African lowlands for the less temperature sensitive species. These results imply the current range of these forest trees does not necessarily inform risk from climatic change, and that human land-use may be the major pressure for many species in the future.