Abstract:

On two occasions, with a 10- or 11-year interval, species occurring in 650 plots (100 m2) in boreal production forests in Sweden were recorded within a monitoring program. During this interval, many of the plots had been subjected to varying degrees of timber extraction. The presence of 49 vascular plant species or species groups was recorded and we evaluated how species number varied over time. There was an overall increase in species number, probably partly reflecting changing attitudes and strategies for fieldwork. Logging had a modest, but significant positive effect on the change in species number per plot. When analysing individual species, three of 18 showed a differential response along the logging gradient: Linnea borealis was more likely to appear at low logging intensities while the opposite pattern was present in Epilobium angustifolium and Calluna vulgaris. A species turnover index was calculated per plot and used as the dependent variable in a multiple regression with six independent variables. Three of these contributed significantly to the model: turnover increased (i) with decreasing amounts of Pinus sylvestris in the tree canopy; (ii) with increasing site productivity; and (iii) with increasing logging intensity. Hence, greatest changes over time occurred in stands lacking P. sylvestris (consequently dominated by Picea abies) that occurred on fertile soil, and was amplified by logging.