Regeneration of the East African timber tree Ocotea usambarensis in relation to historical logging

Abstract

East African montane forests have been subjected to heavy logging, particularly of Ocotea usambarensis Engl., formerly one of the dominant tree species of moist mid-altitude forests. At Mt. Kenya, logging was suspended in 2000 after a conspicuous decline in population size, but the success of this conservation measure has not yet been evaluated. Given that a management scheme of O. usambarensis forests based on vegetative regeneration has been suggested, we hypothesized that natural regeneration mainly by root suckers would be sufficient for a recovery of this species. Demography and regeneration (both sexual and vegetative) of O. usambarensis were studied in 45 study plots between 1700 and 2500m asl along a gradient of historical logging intensity, while taking altitude and light incidence into account as predictor variables. The diameter distribution showed a high percentage of old individuals and rather low recruitment in O. usambarensis. In heavily logged areas (removed basal area >25m2ha−1), smaller trees (<50cm DBH, >130cm high) were completely absent. The number of seedlings was low and independent of logging intensity. It increased with higher light incidence. The number of root suckers was 5.6-fold the number of seedlings, underscoring the importance of vegetative reproduction. However, number of root suckers and logging intensity were negatively correlated. We conclude that regeneration of O. usambarensis at Mt. Kenya is generally low and negatively influenced by historical logging. Therefore, natural regeneration is inadequate for the recovery of this valuable timber species, and additional conservation measures such as enrichment planting should be considered.