Determining the response of African biota to climate change: using the past to model the future

Abstract

Prediction of biotic responses to future climate change in tropical Africa tends to be based on two modelling approaches: bioclimatic species envelope models and dynamic vegetation models. Another complementary but underused approach is to examine biotic responses to similar climatic changes in the past as evidenced in fossil and historical records. This paper reviews these records and highlights the information that they provide in terms of understanding the local- and regional-scale responses of African vegetation to future climate change. A key point that emerges is that a move to warmer and wetter conditions in the past resulted in a large increase in biomass and a range distribution of woody plants up to 400–500 km north of its present location, the so-called greening of the Sahara. By contrast, a transition to warmer and drier conditions resulted in a reduction in woody vegetation in many regions and an increase in grass/savanna-dominated landscapes. The rapid rate of climate warming coming into the current interglacial resulted in a dramatic increase in community turnover, but there is little evidence for widespread extinctions. However, huge variation in biotic response in both space and time is apparent with, in some cases, totally different responses to the same climatic driver. This highlights the importance of local features such as soils, topography and also internal biotic factors in determining responses and resilience of the African biota to climate change, information that is difficult to obtain from modelling but is abundant in palaeoecological records.

Assessing the effects of climate change on distributions of Cape Floristic Region amphibians

“…Examples of such changes include the occurrence of lakes and 'forest-elements' within the current Sahara region (between 11 kya and 4 kya, under warmer and wetter conditions) and the replacement of forest by savannah vegetation in equatorial west Africa when conditions are predicted to have been warmer and drier than present. 7 Studies undertaken in southern Africa, particularly in the Cape Floristic Region (CFR) suggest that climate has remained relatively stable throughout the Quaternary. 5 Indeed, areas such as the CFR that are proposed to have experienced relatively stable climate coincide with contemporary centres of richness and narrowly distributed endemic species.…”

The past, present and future of Africa's rainforests

“…Willis et al [9] describe the history of climate variation in Africa since the last Ice Age, again narrating a story of change and periods of retreat and advance of forests. The story emerging is of a rainforest biome that has undergone varying levels of human and climatic pressure over time, and that these changes may be reflected in the current structure and composition of the African forests, and their potential for resilience to present and future change.…”

The ‘cultured rainforests’ of Borneo

“…Within many such initiatives, the long-term monitoring of trends in ecological change is increasingly prioritized to improve future predictive capacities, yet even with these goals most ecologists study organisms on a time scale of less than 100 years, only a fraction of a single generation of many rainforest canopy trees (Ashton, 2014). Clearly a deeper temporal perspective is needed to understand many long-term patterns and processes affecting rainforests, including human impacts (Willis et al, 2004; Willis and Baghwat, 2010;Willis et al, 2013). The role of palaeoecology, especially palynology, is clearly paramount in such investigations, but in this paper we have argued that the combination of palaeoecological and archaeological approaches, informed by anthropological studies of recent and present-day rainforest societies, provides powerful complementary insights into human-rainforest history.…”