Boom-corridor thinning (BCT) is a harvesting operation method that increases efficiency and cost-effectiveness by thinning strips in young dense stands of a defined size with boom-tip harvesting technology. Different boom corridor patterns and how they are applied give different degree of selective tree selection.

For example, using a fan-shaped pattern (see Figure), “laid out” by the decision of the operator, will give higher degree of tree selection than of using a perpendicular pattern laid out strictly systematically. Research has shown that 1) the combination of BCT and new felling technologies during biomass thinning operations can significantly increase the harvesting efficiency, and 2) decrease supply costs by 12–27% when conventional selective thinning and standard handling procedures are replaced with a BCT system that includes innovative biomass compaction and transportation methods. Research also reports that BCT systems are most efficient at harvesting trees under 30 dm3, a size class that represents a significant portion of the potential annual harvest in young stands in Sweden.

BCT techniques facilitate cost-effective management of young stands and also allow aspects other than wood production to be taken into account. For example, there has been a growing concern about how forest management plans can include ecosystem services and environmental goals without jeopardizing the production of valuable biomaterials.

It has been suggested that stand heterogeneity and vertical complexity promotes various ecosystem services. Researchers have begun to classify the various ecosystem services so they can be recognized by forest management plans. However, the stand structure resulting from a management regime cannot only cater to ecosystem services, but must present a cost-effective solution as well. In this way BCT is an attractive option from a forest management perspective, as it is both cost-effective and should create a more complex vertical stand structure than conventional thinning. This is because BCT methods, when strictly used, only cut trees from pre-defined areas, leaving certain areas, or strips, untouched and with their natural stand structure.

On the other hand, commercial selective cutting, which includes the preclearance of any undergrowth with a stem size smaller than the commercial size, thins, in general, an entire stand to a homogeneous area containing only larger diameter trees for future harvest. In this way, the first thinning phase largely determines the stand structure for a majority of the stand rotation period. There are many thinning operations to choose from, and each can result in a different stand structure and thus different possible values.

Reference: Ahnlund Ulvcrona, K., Bergström, D. & Bergsten, U. 2017. Stand structure after thinning in 1–2 m wide corridors in young dense stands. Silva Fennica, 51(3), id 1563.


Text: Dan Bergström, SLU