Modelling above-ground stem volume and tree biomass for Searsia lancea (L.f.) f.a.barkley in central bushveld, South Africa
Hawassa University, Wondo Genet College of Forestry and Natural Resources (WGCF-NR), General Forestry, Ethiopia
The aim of this study was to estimate the above-ground stem volume and tree biomass of the multi-stemmed Karee tree (Searsia lancea) for its potential use for producing wood chips and/or pellets. A stratified random sampling was done, by selecting two blocks with both sparse and dense Karee stands. In each block, three sparse and three dense Karee stands were identified. Within each block, three thinning treatments of only Karee stems (no thinning, 50% thinning and 100% clearfelling) were randomly allocated to the selected stands. On each circular plot, all trees with stem diameter at breast height (DBH) of ≥5 cm were recorded by tree number, stem diameter and species. A 50% thinning in sparse stands produced a stem volume of 11.92±6.28 m3 ha-1; and total dry biomass of 8.51±3.63 t ha-1; and in dense stands it produced a stem volume of 22.97±4.38 m3 ha-1; and total dry biomass of 16.05±2.42 t ha-1. The clear-felling (100% thinning) in sparse stands produced a stem volume of 14.10±4.01 m3 ha-1; and total dry biomass of 10.02±4.48 t ha-1 and in dense stands, it produced 60.64±22.97 m3 ha-1; and 33.80±2.25 t ha-1. To assume linearity, tree data were logtransformed to develop species-specific models (the first for Karee). Coefficient of determination (R2), residual standard error (RSE) and residual mean squared error (RMSE) were used as model performance metrics. Akaike Information Criteria (AIC) was used as final criteria for selection of the best model in which the model with lower AIC was selected. Finally, the developed models were used to compute stem volume, tree biomass and carbon stock of all sampled Karee trees: In sparse stands, mean stem volume was 19.92±4.34 m3 ha-1, tree biomass was 13.33±2.14 t ha-1, and carbon stock was 6.67±1.07 t ha-1. In dense stands, mean stem volume was 47.09±3.98 m3 ha-1, tree biomass was 31.76±3.99 t ha-1, and carbon stock was 15.88±1.99 t ha-1. Generally, if sustainably managed, Karee can be used as a potential energy source by producing pellets for use as bio-energy.
Keywords: Bio-energy, carbon, clear-felling, Karee, multi-stemmed, stem diameter, stem length, stem thinning, stem volume, tree biomass
Contact Address: Kassahun Maru, Hawassa University, Wondo Genet College of Forestry and Natural Resources (WGCF-NR), General Forestry, 128, 251 Hawassa, Ethiopia, e-mail: kasahun4gmail.com