Timber yield determination and allocation in selective logging system in Ghana

Timber yield determination and allocation in the selection forest of Ghana has been on an interim basis due mainly to paucity of stand increment and mortality data. The current method, which is also an interim measure. was developed at the Forestry Planning Office in 1990 to replace the minimum felling diameter limit introduced in 1970 to salvage the over-mature trees over a period of 15 years. This paper reviews the mathematical logic of the current interim yield formula. The formula is modified by considering current data on mortality, felling cycle and time of passage. The idea of optimizing yield by number of stems per hectare is also applied in this revised version. The study reveals that one important premise in the derivation of the current interim formula was put in an incorrect algebraic form. resulting in an over-allocation of yield for individual species. A comparative analysis of the original and revised forms of the yield formula indicates that the latter is more effective in ensuring sustainability and is easily adaptable to different forest types, stocking levels and management prescription of felling cycle. /n the revised form, the effect of the ratio between felling cycle and time of passage (FIP) on yield is very significant. To fine-tune the revised form. more accurate data on the time of passage for the various species of different diameter classes in different forest types are essential requirements.