Effects of partial cutting on logging productivity, economic returns and dead wood in boreal pine forest

Structural diversity of forests is important for biodiversity. In managed forests, structural diversity can be maintained by retaining living and dead trees, and by creating dead wood during logging operations. In Sweden, a small percentage of the trees is currently retained on each clear-cut. Since retention decreases revenues from forest harvesting, it is important to understand the consequences of retention for both forestry economy and biodiversity conservation. Thus, in this study we compared effects of retaining percentages ranging from 5% to 50% of the initial number of trees in 12 Scots pine-dominated stands in central Sweden. The retained trees in each stand consisted of equal proportions of green living trees, felled trees, high-cut trees and girdled trees. We estimated costs associated with tree retention and, as indicators of biodiversity conservation values, dead wood volumes, number of dead wood types, and dead wood diversity. We also estimated the damage caused by the logging operations on old dead wood. Revenue declined with increases in retention level, due mainly to associated reductions in harvested volumes, but partly to increases in logging costs. Both harvester and forwarder performance were lower at high than at low retention levels. The volume of dead wood increased with increases in retention level, since the number of retained trees killed per stand was proportional to the retention level. The number of dead wood types and dead wood diversity increased continuously up to the highest retention level of almost 50%. Moreover, old dead wood that was deemed particularly valuable for biodiversity was not destroyed at retention levels above 30%. In conclusion, dead wood destruction decreased with increasing retention level and costs increased proportionally to the retained volume. There were no signs of saturation of dead wood diversity as retention level increased. Therefore, mainly economic restrains will determine the retention level.