Population Structure of Prunus africana (Hook. f.) Kalkm. and Olea europaea L. in South Nandi Afromontane Forest, Kenya

Prunus africana (African cherry) and Olea eurpaea (Olive) tree species from the moist highlands of sub-Saharan Africa are subjected to industrial-scale harvesting, and therefore endangered due to their medicinal values and fine wood. Studying their population dynamics plays an important role in identifying the conservation needs in tropical ecosystems. This paper focuses on an ecological study carried out from April-June 2017, within the South Nandi Afromontane Forest, Kenya. The objectives were to analyse population density, diameter size class distribution, and the horizontal structure of Prunus africana and Olea europaea species as indicators of their respective species stability within the forest. Two-line transects established 250 meters apart were used to lay twenty systematic sample plots of 50 m x 20 m each, along with a transect at an interval of 200 m. These sample plots were further divided into five sub-sample units of 20 m × 10 m, where the number of trees with Diameter at Breast Height (DBH) >10 cm, poles 5-10 cm, saplings 1-5 cm were assessed, while the number of seedlings with DBH < 1 cm were assessed in 50 m × 1m bands within the sample plots. Two and one-way Analysis of Variance ANOVA were applied at a 5% level of significance. The population densities ranged from 860-885 stems/hectare for P.africana and 569-601 stems/hectare for O. europaea, and were significantly different (p<0.05) along the transects and between the sampled cluster sites of Chebilat, Kobujoi, Chepkongony, and Kamarich, within the South Nandi Forest. Diameter size class distribution took the shape of reverse ‘J’ curve, which characterises stable populations that naturally replace themselves through regeneration. However, in comparison with United Nation Organisation 1994 model for structurally stable East African natural forest ecosystems, the species were unstocked, which indicates low recruitment from seedlings into mature trees due to possible anthropogenic disturbances. Recruitment of both species occurred more intensively in canopy gaps but displayed inhibition near mature conspecifics throughout the forest floor. There is a need to consider population densities, regeneration, and recruitment levels in planning to restore the two species through artificial regeneration, in addition to advocate for strategic in-situ conservation interventions to enhance recruitment in South Nandi Forest.