The recovery of an afromontane forest after slash and burn : a case study from the Nkandla forest.

Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2000.

Clear cutting and subsequent agricultural processes lead not only to species loss, but also have negative consequences for soil and water conservation. This study investigated the response to, and effect of, deforestation due to shifting cultivation on the Nkandla forest complex (NFC), a subtropical Afromontane forest. As a consequence of shifting agriculture, abandoned areas are nutrient poor, have depleted seed banks and may lack the ability to regenerate into species rich mature forest. The ability of forests to regenerate after disturbance effects is extremely important for the maintenance of ecological diversity and the stability of forest ecosystems. The present study focused on the recovery of the NFC, after shifting agriculture was practised along the forest margins. The NFC was sampled to determine: (1) how vegetation structure, composition and plant species diversity differ between regrowth forest and undisturbed forest ; (2) how continued disturbance and subsequent land use affects the rate of recovery and regeneration of secondary forest ; and (3) what species establishment pattern, if any, does the path of recovery follow during succession? Four different types of forest were sampled, disturbed margin (DM) forest, disturbed interior (DI) forest , undisturbed margin (UM) forest and undisturbed interior (UI) forest. The study showed that recovery does occur and that in the NFC recovery patterns (in terms of species diversity trends, biomass and basal areas) are similar to those found in other tropical and sub-tropical regions. Floristic recovery proceeded in a way that required the prerequisite establishment of forest margin tree species that would ultimately lead to a climax condition described by undisturbed interior forest. Unimodal trends were found for stem density and species richness across all four forest types, with basal area increasing steadily from disturbed to undisturbed interior forest. These forest types and their floral composition and structure described a gradient of decreasing disturbance, with disturbed margin forest being the most disturbed type. Continued harvesting of selected species is detrimental to the survival of these species. Analyses showed that Rapanea melanophloeos, Cassipourea gummiflua, Curtisia dentata, Ochna natalitia, Olea capensis subsp. macrocarpa and Strychnos henningsii have been overused. Continued harvesting could result in critically low densities of these species and even their local extinction.