Birch shelterwood removal – harvester and forwarder time consumption, damage to understory spruce and net revenues

Abstract

ABSTRACT To improve the micro climate for Norway spruce (Picea abies (L.) Karst.) regeneration and achieve higher growth, a system of birch shelterwoods with naturally regenerated birch (Betula spp.) creating an overstory sheltering planted spruce is implemented in southern Sweden. Even though the primary objective is to establish a new spruce stand, the economic viability depends on efficient birch overstory harvest with little damage to spruce regeneration. This study aimed to analyze time consumption and net revenues for harvester and forwarder work when removing the birch overstory, and to describe the frequency of logging damage in the residual spruce stand. Time consumption data was collected through time studies of harvesting and forwarding of 10 study plots. Sample plots were inventoried after harvesting and forwarding operations to identify damage on the residual spruce. Average harvester productivity was 2.8 oven dry ton per efficient work hour. The variation in time consumption was up to 94%, explained by a positive correlation with the number of trees harvested per hectare and a negative relationship with removed volume per hectare. Forwarder loading time correlated with forwarded volume along the strip road and the number of birch trees per ha prior to logging. Approximately 7–17% of the residual trees were damaged, and the harvester caused 83% of the damage. Due to high harvesting costs and low revenues, only plots with large removals provided positive net revenues. Birch shelterwoods can therefore not be expected to increase net revenues but are best seen as a regeneration method for addressing stand re-establishment challenges.