Wood Basic Density of Common Woody Species of Lowland Forest in Borana Woodland, Southern Ethiopia

Abstract

Understanding wood basic density and its variability is crucial for accurate biomass estimation and carbon stock assessment. This study investigated wood basic density of five dominant woody species (Euclea divinorum, Teclea nobilis, Olea europaea, Oncoba spinosa, and Commiphora africana) in the Gamadu forest of the Borana woodland, southern Ethiopia. A total of 114 trees were sampled, with stem and branch disks collected to quantify mean wood basic density values and examine variations across and within species. Generalized additive models and partial correlation analyses were applied to evaluate the effects of site conditions and tree size. Results showed significant interspecific variation in stem wood basic density (p < 0.001), ranging from 0.37 to 0.967 g cm-³, with a mean of 0.70 g cm-³. Across all species, branch wood basic density was significantly lower than stem wood basic density by an average of 0.142 g cm-³ (p < 0.001). Generalized additive model identified tree species and diameter at stump height as significant predictors of stem wood basic density, while site disturbance level, land slope and hill position showed no effect. Stem diameter exhibited a positive linear influence, and tree height had a weak but significant non-linear relationship. Partial correlations further indicated a moderate positive association between stem wood basic density and diameter (r = 0.3924), and a weak correlation with height (r = 0.1593). These findings demonstrate that variation in wood basic density are influenced more by tree-specific biological traits than by site-related factors. The study provides valuable data to enrich global wood density databases and improve biomass and carbon estimation models in dryland forest ecosystems.