Performance of Harvesting Residue Treatment Methods in South African Pine Plantations

Abstract

Forest harvesting generates variable amounts of residue that pose a fire hazard and a hindrance to regeneration and must be managed accordingly. In South Africa, burning is the most common residue management method, but there is interest in introducing safer and more effective techniques, such as mulching. For that reason, a productivity study was conducted in the Eastern Cape province after a mechanised cut-to-length (harvester and forwarder) harvesting operation to gather information on the productivity, cost, and work quality of the three main alternatives: manual broadcasting, manual broadcasting followed by mulching with an adapted farm tractor and mulching with a purpose-built mulcher. The stem wood residues after harvesting ranged from 12 to 14 ODT/ha. The average time consumption was 16 worker h/ha for manual broadcasting, 3.6 worker h/ha for mulching with a farm tractor, and 0.9 worker h/ha for mulching using a purpose-built mulcher (one pass). Manual broadcasting was the cheapest option, at an average cost of 400 ZAR/ha. Mulching with a farm tractor and a purpose-built mulcher incurred an average cost of 3267 ZAR/ha and 4083 ZAR/ha, respectively. Manual broadcasting achieved a minimal reduction in residue size, with 50% of the slash (branches and stem wood) having a mean length greater than 40 cm. When mulching with a farm tractor was applied, 49% of the slash (branches and stem wood) length was reduced to about 30 cm. When a purpose-built mulcher was used, only 10% of the slash elements exceeded 40 cm in length.