Regeneration of fourteen tree species in Harenna forest, southeastern Ethiopia

Abstract

Summary Regeneration of fourteen tree species was investigated at Harenna forest, on the southern slopes of the Bale Mountains, Ethiopia. Tree seedling densities and their spatial distribution along gradients of altitude and light were investigated using quadrats of 10 m × 5 m along line transects. Seedling mortality and herbivore damage were examined in eight permanent plots of 10 m × 5 m laid systematically at different places. Population structures of the species were investigated using quadrats of 20 m × 20 m along line transects. Species showed variation in densities of their seedlings ranging from 1065 to only 58 seedlings per hectare.Frequency of distribution of species along altitudinal gradients varied between 15 and 69 percent, indicating differences in habitat preferences among the species. In their spatial distribution to the canopy light gradient, eight tree species were found growing under canopy shade (1–5% light level) while six grew exclusively in the open (100%). More than 42% of the populations of seedlings investigated during the dry season of the year were damaged by herbivores and 27% were lost as uprooted, died and standing or were missing. Examination of the population structure of the species showed that only few species had good representation of individuals at all size classes implying healthy or normal regeneration. Many of the species showed strong peak at lower size classes followed by missing of individuals at one or more of the medium and upper height classes, which indicated that regeneration was hampered. Tree species with healthy regeneration or reverse “J” distribution included Teclea nobilis , Ocotea kenyensis and Syzygium guineense subsp guineense , whereas Podocarpus falcatus , Aningeria adolfi-friederici , Olea capensis , Croton macrostachyus and Prunus africana showed hampered regeneration. Management alternatives to enhance regeneration status of the species are discussed.