Podocarps in Africa: Temperate Zone Relicts or Rainforest Survivors?

Podocarp distribution in Africa follows a discontinuous mountainous belt from Cameroon to Angola in the west and from Ethiopia in the northeast to the southern Cape in South Africa. Besides a relict population of Afrocarpus falcatus in coastal lowland forest in northeastern South Africa and southern Mozambique, African podocarps are generally limited to highland (Afrotemperate) regions. All podocarps are restricted to montane regions in Madagascar. Afrotemperate landscapes are characterized by a patchy mosaic of forest and grassland. Processes in the matrix, such as fire, are important drivers of forest distribution in the highland regions. Here we examine the relative performance of podocarps and angiosperms along an altitudinal gradient from temperate highlands to subtropical coastal regions in eastern South Africa. Podocarpus latifolius is a successful component of temperate highland forest, where it dominates oldgrowth stages. The success of podocarps is attributed to their greater longevity and ability to regenerate in shade, whereas many potential competing angiosperms are less capable of doing so. Regeneration by P. latifolius and associated angiosperms is less successful in highlight gap environments, where ferns and grasses suppress establishment. Podocarps are rare in coastal scarp forest, where the population is dominated by adult individuals. They are unable to regenerate in very deep shade (<3% daylight), which may account for the lack of P. latifolius regeneration beneath the dense canopy of coastal scarp forest. Lownutrient soils did not favor podocarps over angiosperms, although the fact that soil nutrients do not appear to be limiting and the scarcity of shadetolerant angiosperms in forests may influence this outcome. The relative role of light and soils on angiospermconifer competition is unknown for lowland forest, although current evidence from montane forests suggests that under prevailing soil conditions, light is the more important axis of niche differentiation.