Systems analyses for harvesting small trees for forest fuel in urban forestry

Forests in urban areas are important for recreation. Social, aesthetic and recreational values are at least as important for forest management as economy and conventional forestry considerations. Systems with short, intensive harvesting phases and limited damage to ground and trees are also advantageous, in order to reduce disturbance through harvesting operations. Further, slash free stands constitute a more attractive environment for recreational activities. Forest fuel harvesting may provide these conditions. This study analyses the economic feasibility of harvesting forest fuel in dense, small diameter stands. The analyses are performed as simulated treatments in selected stand types. Both existing and non-existing forest fuel systems are tested. Conventional cleaning and conventional thinning for pulpwood are included as reference systems. The average dbh of removed trees varied between 3.0 and 10.5 cm. The potential yield of biomass in the studied stand types is high—under Swedish conditions over 35 tonnes dry substance per ha. Harvesting pulpwood exclusively means that only a small portion of the potential is utilised. Forest fuel systems based on motor–manual work are the most competitive in the smallest diameter stands. They break even from dbh 4.5 cm in birch stands and from 5.5 cm in pine. Simulated systems include a feller–chipper–forwarder and a two-machine system with a feller–bundler and a forwarder. Both are suitable for larger tree sizes than the manual methods. The conventional pulpwood method shows the poorest result, but start competing with the poorest forest-fuel systems from dbh 10 cm (removed trees).