Influence of Thinning Regime on Woody Species Density and Abundance in Kimondi Forest, Nandi County, Kenya

A silvicultural regime refers to the planned sequence of treatments applied to a forest stand, which mainly includes pruning and thinning regimes. The latter is a silvicultural practice that is important for the management of forest growth, composition, structure, and health. Despite the ecological and silvicultural importance of thinning, its limited application in plantation forests has constrained the effective management of woody species density and abundance. Thus, the aim of this research was to assess the influence of the thinning regime on woody species density and abundance. This study focused on Eucalyptus saligna, Cupressus lusitanica and Pinus patula as the woody species that are harvested for timber in the Kimondi forest. The study applied a cross-sectional descriptive study design. Systematic sampling was used in collecting primary data. Data were analysed using box plots, Analysis of Variance and Duncan multiple range test. The box plots showed Eucalyptus saligna having the highest median density and the widest interquartile range, indicating both a greater abundance and variability across sampling sites. Cupressus lusitanica and Pinus patula had a moderate median density with a narrower distribution, indicating lower variability. Analysis of variance revealed a highly significant difference in tree abundance and density across the thinning regime (p = 0.000), with an effect size (Eta² = 0.7519), indicating that 75.19% of the variation of woody species density and abundance can be explained by the thinning regime. Duncan’s Multiple Range Test confirmed that mean abundance varied significantly across the thinning regime. The study concluded that a thinning regime can improve the density and abundance of woody species, Eucalyptus saligna, Cupressus lusitanica, and Pinus patula. We recommend that forest managers in plantation forests adopt thinning regimes to improve woody species density and abundance.