Competition and slope effect on wood basic density and its variation among tree species and within individual trees in a dry Afromontane Forest

Abstract

Wood basic density (wbd) is one of the important predictors of aboveground biomass (AGB) of trees. It is subjected to great variability, and different factors explain this variation. Because of interest in the global carbon cycle, estimating forest biomass with sufficient accuracy has become increasingly important. Therefore, assigning accurate wbd values is important to reduce uncertainties in biomass estimations. This study aimed to determine the wbd of the dominant tree species in a dry Afromontane Forest and examine the variation in wbd among species and height positions along the vertical axis of the stem. The effect of competition and slope on wbd was also evaluated. Twelve dominant tree species were targeted and stem discs for wbd determination were collected at three height positions along the vertical axis of the stem for each species. A one-way analysis of variance was carried out to evaluate wbd variations among the species and the three height positions within the trees. A linear mixed effect model was applied to see the effect of competition and slope on wbd. The studied species showed a significant variation in their wbd values. The species-wise overall mean wbd value was 0.75 g cm−3, with a range between 0.607 and 0.911 g cm−3. Only one among the 12 species has wbd value in the Global Wood Density (GWD) database. Competition and slope had a significant effect on wbd, where an increase in competition and slope gradient was associated with an increase in wbd. The obtained wbd data and information can add to the limited knowledge on wbd values of tree species growing in dry Afromontane forests. Moreover, applying the wbd values obtained from this study while estimating AGB using the previously developed multispecies model for Desàa dry Afromontane Forest could significantly improve the accuracy of the biomass estimate.