Evaluation of drone system for thinning operations–a case study in Sweden

Abstract

Thinning operations in forestry typically involve a two-machine system (TMS) with a harvester and a forwarder. Its productivity in different forest conditions is well documented. To date, drones have been used for data collection and surveillance but not as an alternative to a TMS. Drone systems are now being developed for thinning operations for removal of smaller trees, but little is known about their productivity and configuration. Two important advantages of drone systems are reduced soil damage and CO₂ emissions. We propose an evaluation approach that describes drone systems in detail and enables a direct comparison with a standard TMS. This approach is then tested on a large case study comprising 1171 harvest areas with diverse characteristics with regard to, for example, flying and forwarding distance, wetness, and steepness defined through detailed digital terrain models. We perform sensitivity analyses on a set of drone system configurations regarding the number of drones, battery system, system parameters, automation level, CO₂ tax level, and soil damage cost. The results show that the drone system requires less energy, but with no automation and only four drones in a system, the TMS system is more competitive in virtually all harvest areas. However, with eight drones in a system and a higher automation level, the drone system is competitive in up to 50% of the harvest areas. This figure increases if a CO₂ tax and a cost related to soil damage are included.