Succession and Regeneration Patterns of East African Mountain Forests. A Review

Abstract

Regeneration and succession processes in montane forests of Kenya and parts of Ethiopia were investigated. The slowly growing camphor tree, Ocotea usambarensis, regenerates mainly by suckers from old root systems. Undamaged seeds were very rarely seen, and, apparently are viable only for a few days. After natural breakdown of an old tree, the gap is filled by fast growing species, mainly Macaranga kilimandscharica and Neoboutonia macrocalyx, in the shade of which the young Ocotea suckers can establish. After the death of the secondary species, whose germination requires full sunlight and is inhibited in the shade, the Ocotea forest recovers. Large scale logging of Camphor trees predominantly destroys the regeneration of Ocotea and leads to secondary forest types, which regenerate in own cycles. The high number of big game was found to be without impact on the natural regeneration of Ocotea. The Cassipourea malosana dominated forest regenerates as a mosaic-climax without a single species becoming dominant. Cedar forests dominated by Juniperus procera regenerate most efficiently after fire. Without recurrent burning, the forests of the lower and middle part of the montane zone, regenerate to climax associations dominated by broad-leaved trees as Olea capensis ssp. hochstetteri, Olea europaea ssp. cuspidata and Podocarpus latifolius. On higher altitudes Juniperus procera always remains dominant even if fire does not occur for a longer time period. The high population density especially of buffaloes seems to inhibit successful regeneration in many parts of the Juniperion, due to intensive browsing and in particular trampling. The African Bamboo, Sinarun- dinaria alpina, shows a distinct growth cycle and can grow for extremely long periods in the vegetative state before flowering, especially so at the borders of its area. After flowering and dying of the bamboo, in most areas a dense Sambucus africana shrub is formed into which bamboo is invading from old rhizomes again. In Ethiopia, regeneration occurs directly, without an interspersed Sambucus stage. The uniform age of the Hagenia stands suggests that regeneration in these forests occurs suddenly after a disturbing event. Germination tests yielded, that Hagenia seeds are not germinating unless the competing undergrowth is removed. As fire is the only natural factor able to clear the grass layer of larger areas, it is assumed, that the reproduction of the subalpine forests depends on occasional burning.