Palynological Intimations on the East African Mountains

A number of important pollen diagrams from high altitudinal sites in East Africa cover the time of the Last Glacial Maximum (LGM) and provide similar data on the palaeoenvironment of these regions for that period. However, the interpretation of the results and the explanations of the causes of these environmental changes have been the source of some debate during the last decades. The present review, based on comparison of present-day and LGM climatic data, indicates that although rainfall is rightly considered to be an important parameter in biographic discussion, it is temperature that is the dominant primary cause of major palaeoenvironmental change. The considerable drops in sea surface temperature (SST) during LGM times in both the Benguela and Agulhas Currents strongly influenced the advection of humidity to Central and East Africa causing severe aridity on plateaus and high mountains. Cloud formation and the distribution of precipitation on the high mountains are temperature dependent. In LGM times with lower evaporation of the ocean surface, the mountains were generally drier, the cloud belt developed at lower altitudes and the harsh diurnal climate extended downward, lowering the tree line and reducing the extent of the forest. This phenomenon is clearly demonstrated by the total fossil pollen assemblages from each of the six high altitudinal sites in which similar elements were recorded. During LGM times the sites were in most cases surrounded by alpine desert indicating aridity and colder conditions at these altitudes.