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

The deciduous Vaccinium myrtillus and the evergreen Vaccinium vitis-idaea w ere subjected to five removal treatments of understorey layers control, rem oval of the moss laver, removal of the field layer, removal of both moss an d 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 stud ied 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 wh ich production of new ramets was virtually absent throughout the study. Ful l recovery following removal of the field laver only or both field and moss layers was reached after four years for V myrtillus. V. vitis-idaea recove red more quickly, after one year (removal of field layer only) and four yea rs (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 densit y increased after sowing in the most severe treatment. The results undersco re the importance of vegetative growth for recovery of these species at mod erate-level disturbances. The high rate of sexual reproduction in the most severe treatment implies that strong mechanical disturbance is needed to en hance the establishment of new genotypes in these species.