The implication of using a fixed form factor in areas under different rainfall and soil conditions for Pinus kesiya in Zambia

The study was undertaken to evaluate form factors for Pinus kesiya growing in the three Zambia Forest and Forestry Industries Corporation (ZAFFICO) plantations – the Ndola, Ichimpe and Chati groups – under different rainfall (900–1 500 mm) and soil conditions (pH 4.0–5.5). Trees were sampled from the three plantation groups and 10 sample plots were established in which 10 trees were randomly sampled for cutting. Height and diameter at breast height (dbh) were the main variables that were measured and constituted the collected data. The trees were then felled and cut into segments of 0.5 m from the bottom to the top of the tree and segment diameters over bark were measured at both ends. The form factor for each tree was then calculated by dividing the sum of the volume of the tree segments by the estimated cylindrical volume of the standing tree. The results showed significant differences (p-value<0.05) in form factors among the three plantation groups. The study further showed a significant difference in form factor when the three plantation groups were compared with a fixed form factor (0.4) used by ZAFFICO plantations, indicating that the form factors are site specific. Therefore, for the benefit of customers and plantation owners, it is important that area-specific form factors should be used for each plantation group, as these groups are affected by different factors such as soils characteristics and rainfall, which have a direct effect on the form factor.