Concepts for mechanized tree planting in southern Sweden

Sammanfattning: The underlying reason for mechanizing tree planting in southern Sweden is the biologically good planting results produced by today's tree planting machines. Nevertheless, the productivity of these tracked excavators with crane-mounted tree planting devices is too low for them to compete economically with manual planting. The objective of this thesis was to investigate concepts for 1) seedling packaging, 2) base machines, 3) planting devices, and 4) seedling carousels that could cost-efficiently increase the productivity of today's planting machines in southern Sweden. Article I analyzed the cost-efficiency of two seedling packaging concepts that decrease the time needed to reload planting devices with seedlings. The analysis showed, however, that machine-specific seedling packaging was costlier than delivering the seedlings in their cultivation trays, although band-mounted seedlings will probably be the most flexible and cost-efficient packaging system as mechanized planting becomes more common. Article II and III used a discrete-event simulation tool and detailed terrain, machine, and planting device models to simulate the productivity of conceptual two-armed excavators and multi-headed crane-mounted planting devices. Two arms per excavator proved to be an inefficient concept for increasing the productivity of today's planting machines when compared to multi-headed planting devices. Although four planting heads per device was the most productive configuration on easy to moderate terrain, three-headed devices were best at combining high productivity with acceptable silvicultural results on all terrain types. Article IV used a test-rig to study the feasibility of tray-wise seedling reloading on today's most common planting device. Seedling reloading was twice as fast when done tray-wise rather than seedling-wise, and deplugging proved to be a reliable method of extracting seedlings from suitable cultivation trays even when performed at the excavator’s boom-tip during mounding work. Overall, this thesis confirms that there is high potential for technical improvements that increase the productivity and lower the planting costs of today's tree planting machines. Such improvements will likely include faster seedling reloading via tray-wise-loaded carousels or band-mounted seedlings, multi-headed planting devices that produce high quality planting spots using adapted soil preparation methods, and sensors that aid the operator in choosing microsites.

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