Variation in Regeneration Density and Population Structure of Prunus africana Across Human Disturbance Gradient in South West Mau Forest, Kenya

Abstract

Prunus africana has been severely exploited for its valuable products rendering it unstable and at risk of extinction. Studies were therefore carried out on its regeneration density and population structure across different human disturbance gradients in South West Mau Forest (SWMF) Kenya. Four study sites with {undisturbed, low, moderate and high} human disturbances were identified in SWMF. In each study site three line transects, 100 m apart and running up to 1 km inside the forest were established. Four sample plots 20 m x 50 m were laid at 250 m intervals along each line transect then divided further into 10 subplots each 10 m x 10 m and nested 5m x 5 m sub-subplots. At the centre of each sub-subplot, a 1 m x 1 m quadrant was laid. In each sub plot Diameter at Breast Height (DBH) of all adult trees and poles were measured while the number of saplings in each sub-subplot and seedlings in each quadrant were counted. Light screening efficiency was evaluated in all study sites as an indicator of canopy openings. One way Analysis of Variance (ANOVA) was used to test for significant differences of the studied variables, Tukey Post Hoc test was used in pairwise mean comparison and parametric Pearson correlation analysis was used to test for relationship between variables. Bar graphs and line graphs were used to depict trends in population structure and diameter-size distribution respectively. Animal trails, old charcoal production sites, tree harvesting and debarking of P. africana were found as significant human forest disturbances (p < 0.05) that negatively influenced its relative abundance (r = -0.077). Canopy openings as consequence of disturbance negatively influenced its regeneration density (r = -0.089). The relatively undisturbed site of the forest had a stable population structure for P. africana that followed reverse-J curve irrespective of the high debarking rate (90%) that decreased across the disturbance gradient. These findings suggest a need for designing sustainable management strategies that will lead to rehabilitation, restoration and monitoring of P. africana population dynamics in SWMF.