Operational analysis of a hydraulic shear–chainsaw composite harvester head for low-stump harvesting in Acacia plantations

Mechanized harvesting of tropical Acacia plantations is essential for the pulp-and-paper industry, yet highly abrasive soils and heterogeneous tree morphologies limit the efficiency of conventional single-chainsaw harvesting heads. This study evaluated a novel shear-chainsaw composite harvester head featuring vertical functional zoning through time-motion studies of 215 trees (a morphology-enriched trial sample) in an Indonesian Acacia plantation. A four-category classification (standard, base-only anomaly, crown-only anomaly, and compound anomaly) was introduced to analyze three operational phases: aligning, felling, and delimbing-bucking. The composite system operated at the nominal 50-mm stump-height target set by the project client under the observed trial conditions; the bottom hydraulic shear performed the near-ground stump cut, keeping the larger lower main chainsaw – used primarily for stem bucking – away from the stump-cut position. A scenario-based estimate indicated 1.21–1.44 m3 ha−1 of potential incremental stem volume (modeled gross value USD $97–115 ha−1) under the stated assumptions. Temporal analysis showed that delimbing-bucking was the dominant recorded head-centered time component, accounting for 72.4% of total cycle time. Basal anomalies were associated with longer aligning and felling times, whereas crown anomalies were associated with up to 3.9-fold longer delimbing-bucking times compared with standard trees, likely linked to increased crown-related mechanical interference during feeding and delimbing. These findings are consistent with the design intent of balancing tool durability with low-stump harvesting in abrasive environments and highlight the need to consider branch–machine interactions in future hardwood-head development.