Abstract

Timber harvesting operations in plantation forestry in South Africa are rapidly being mechanised. However, machine movement in forest plantations may negatively affect soil quality. The forestry industry is introducing mathematical models to enable it address, limit or at least predict soil damage. One of these mathematical models is the “ProFor” model. The study was conducted in four harvesting sites namely KwaZulu Natal; Eastern Cape and the Western Cape. The impact of mechanised harvesting equipment on soil quality was assessed by observing changes in soil bulk density and critical soil water content. The changes in soil physical properties were then compared with ProFor’s predictions. The results indicated that ProFor gave valid predictions for critical soil moisture content in most of the study sites. However, for observed increases in bulk density, ProFor predictions of soil damage were invalid (r² = - 0.1). The model can be adopted by the South African forestry industry for tactical planning of forest harvesting operations. Additionally, ProFor can be of even more use if a separate algorithm is developed to be used for the prediction of soil compaction which is a common hazard in South African forestry.

Key words: Bulk density, forest harvesting, ProFor, soil compaction.