Mechanised Pine Thinning Harvesting Simulation: Productivity and Cost Improvements as a Result of Changes in Planting Geometry

Traditionally, the removal of entire rows at regular intervals through thinning compartments has been applied to facilitate access to mechanised timber harvesting operations in South Af- rica. These row thinnings have essentially involved the removal of every 7 th row in a standard 2.7×2.7 m planting regime, resulting in a machine trail width of 5.4 m and a theoretical distance to the furthest tree of 8.1 m. A simulation study, based on alternative planting geometries, investigated the effect on har - vesting in terms of harvesting productivity, system costs and impact on stand structure. Compartments of different planting geometries ranging from 2.7 ×2.7 m to 2.5×2.9 m, 2.4×3 m and 2.3×3.1 m at two thinning reference ages were simulator generated. These compartments were then simulator thinned and harvested in the simulation. Results showed that the boom reach of the harvester is optimised by extending row removal from the 7 th to the 9 th row. At the same time, machine trail length per hectare was reduced by 20%. This creates more productive area for tree growth, potentially reduced residual stand impacts, and increases the proportion of selectively harvested trees per hectare. The increased distance between row thinning removals enhanced the potential volume harvested trail length (m 3 /m) and in turn led up to a 8% increase in harvesting productivity, up to a 21% increase in forwarding productivity and a reduction in total costs of up to 7% when changing planting geometry from 2.7×2.7 m to 2.3×3.1 m and 2.4×3.0 m, for first and second thinning.