Stem volume and tree biomass harvested by different thinning intensities from dense and sparse karee stands in Central Bushveld, South Africa

Abstract

The aim of this study was to determine the aboveground 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 cutting, 50% cutting and 100% cutting by number of stems) were randomly allocated to the selected stands. The average moisture content of karee wood was 35.43%. A 50% cutting in sparse stands produced a total dry biomass of 8.51 ± 3.63 t ha−1 and stem volume of 11.92 ± 6.28 m3 ha−1, and in dense stands it produced a total dry biomass of 16.05 ± 2.42 t ha−1 and stem volume of 22.97 ± 4.38 m3 ha−1. The 100% cutting (clear-felling) in sparse stands produced a total dry biomass of 10.02 ± 4.48 t ha−1 and stem volume of 14.10 ± 4.01 m3 ha−1, and in dense stands it produced 33.80 ± 2.25 t ha−1 and 60.64 ± 22.97 m3 ha−1. Thus, the clear-felling biomass was significantly higher than that of 50% cutting, which was supported by ANOVA results for tree biomass (p = 0.0078). In contrast, in terms of stem volume, the p-value was 0.08, indicating that 100% cutting was not significantly higher than the 50% cutting treatment. Dense stands were significantly higher than sparse stands in both tree biomass and stem volume comparisons. Generally, this study showed that there is a great potential to utilise stems of karee for biomass.