Pathfinder: a tool for operational planning of forest regeneration on clearcuts

Abstract Effective forest regeneration is essential for sustainable forestry practices. In Sweden, mechanical site preparation and manual planting is the dominating method, but sourcing labour for the physically demanding work is difficult. An autonomous scarifying and planting system (Autoplant) could meet the requirements of the forest industry and, for this, a tool for regeneration planning and routing is needed. The tool, Pathfinder, plans the regeneration and routes based on the harvested production (hpr) files, soil moisture and parent material maps, no-go areas (for culture or nature conservation), digital elevation models (DEM), and machine data (e.g., working width, critical slope, time taken for different turn angles). The overall planting solution is either a set of capacity constrained routes or a continuous route and could be used for any planting machine as well as for traditional scarifiers as disc trenchers or mounders pulled by forwarders. Pathfinder was tested on eleven regeneration areas throughout Sweden, both with continuous routes and routes based on a carrying capacity of 1500 seedlings. The net operation area, species and seedling density suggestions were deemed relevant by expert judgement in the field. The routes provided by Pathfinder were compared with solutions given by two experienced drivers and a third solution based on the actual soil scarification at the site. Total driving distance did not differ significantly between the suggestions, but Pathfinder included less side-slope driving on steep slopes (≥ 27% or 15°) and medium slopes (15–27%). The chosen threshold value for steep slopes (where side-slope driving should be avoided) affects the routing, and a lower threshold means more turning and longer driving distance. Pathfinder is not only a tool for routing of planting machines, but also helps in planning of traditional regeneration by providing a more correct net area and tree species suggestions based on the growth of the previous stand. It also diminishes the risk of severe soil disturbance by excluding the wettest area in the planning.