Regeneration strategies of dominant boreal forest dwarf shrubs in response to selective removal of understorey layers

. The deciduous Vaccinium myrtillus and the evergreen Vaccinium vitis-idaea were subjected to five removal treatments of understorey layers: control, removal of the moss layer, removal of the field layer, removal of both moss and field layers and removal of moss, field and humus layers. A second factor, sowing, was included to investigate sexual reproduction after disturbance. Density of new ramets and seedlings and growth of annual shoots were studied for the first two growing seasons, whereas cover was measured for five growing seasons after disturbance treatment. Initially, vegetative production of new ramets and species cover increased rapidly in all disturbed plots, except for the most severe treatment, in which production of new ramets was virtually absent throughout the study. Full recovery following removal of the field layer only or both field and moss layers was reached after four years for V. myrtillus. V. vitis-idaea recovered more quickly, after one year (removal of field layer only) and four years (removal of field and moss layers). The relative growth of V. myrtillus and V. vitis-idaea increased in the latter treatment in terms of production of annual shoots and length of annual shoots, respectively. Seedling density increased after sowing in the most severe treatment. The results underscore the importance of vegetative growth for recovery of these species at moderate-level disturbances. The high rate of sexual reproduction in the most severe treatment implies that strong mechanical disturbance is needed to enhance the establishment of new genotypes in these species.