Impact of harvesting machinery on soil physical parameters : evaluation of ProFor model in three main forestry regions of South Africa
Timber harvesting operations in plantation forestry in South Africa are rapidly being mechanised. However, movement of forest machines over the soil increases the potential for soil compaction and disturbance. In an effort to prevent forest soil damage, the Technical University of Munich developed the “ProFor” software. This software enables the calculation of critical soil water content for a given machine and physical soil characteristics. The applicability of ProFor in the South African forestry industry was assessed through the comparison of the evaluation of the impact of forest harvesting machines on soil properties with ProFor predictions. The study was conducted in four harvesting sites located in three of the major plantation forestry regions of South Africa namely: KwaZulu-Natal; Eastern Cape and the Western Cape. The impact of forest harvesting machines on soil physical properties was assessed through the evaluation of changes in soil saturation, soil bulk density and rut depth. The impacts of machine movements on soil physical properties were then compared with ProFor’s predictions. The study has indicated that ProFor gave good predictions of the critical water contents for most of the studied soils except for sandy soils. The study has also indicated that in more than 75% of the observed cases (r = 0.76) ProFor gave valid predictions of rut formation. However, ProFor predictions poorly correlated (r = -0.1) with the observed soil compaction. The model can be adopted for the South African forestry industry for use in the management of wet spots of a plantation. However, ProFor can be of even greater importance if a separate algorithm was built to be used for the prediction of soil compaction which is a common hazard in most South African forestry.