Allometric Equations for Aboveground Biomass Estimation of <i>Osyris quadripartita</i> (African Sandalwood) in Semi-arid Woodlands, Southern Ethiopia

Abstract

African sandalwood, Osyris quadripartita Salzm. ex Decne is cosmopolitan in dry evergreen forest, rocky ridges, and forest edges, habitually with Olea europaea as well as Dodonaea angustifolia woodland in East Africa and Ethiopia. It reaches in Africa from Ethiopia to Algeria and Kenya to South Africa, starting from stunted shrubs to tall trees. Osyris quadripartita is culturally important for herbal medicine and religious activities, and also, commercially for the perfumery oil industry. Recently, the population of the species is endangered in some places, because of overexploitation for commercial values. Even though the species has many economic and ecological functions, its environmental uses like carbon storage and global climate change mitigation are less assessed. Therefore, the study aimed to develop species-specific allometric equations for Osyris quadripartita using a destructive method and to evaluate allometric models for estimating the aboveground biomass (AGB) within the semi-arid woodlands forest of Southern Ethiopia. Subsequently, all the needed biomass calculations were done, eight AGB equations were developed. Based on regression equations AGB is related with a diameter at breast height (DBH), height (H), and density (ρ) both individually and in combination. Out of eight, four allometric equations were chosen based on goodness-of-fit statistics, and the others four are rejected. The chosen models were tested for accuracy supported on observed data. The selected models have best fitted with higher R2-adj and lower residual standard error and Akaike information criterion than rejected equations. The relations for four selected models are significant (p < 0.001), which showed a strong correlation of AGB with selected dendrometric variables. Accordingly, the AGB was strongly correlated with three variables combination DBH, Height & Wood density. Individually, AGB was strongly interrelated with DBH, but not significantly interrelated with height and wood density. A specific species equations are better for determining biomass and carbon evaluation than general equations.