Optimum timing of soil scarification for the natural regeneration of Pinus sylvestris in Central Sweden

In an attempt to identify the optimal time for soil scarification to promote the natural regeneration of Pinus sylvestris L. (Scots pine), scarification was applied at various times in two pine shelterwood stands, from autumn 2005 to spring 2006 in one and from autumn 2006 to spring 2008 in the other. Each year, seed fall was monitored from April to July and numbers of emerged seedlings were counted at the end of the vegetation period. The number of emerged seedlings was closely related to the proportion of unshed seeds remaining in the cones at the time of each scarification event. A significant difference was observed in seedling establishment between scarification in the autumn and the following late spring, but not between scarification in autumn and early spring. Both the level of seed production and the timing of scarification in relation to seed fall proved to be important determinants of seedling densities, but during 2008 a promising seed fall did not result in good seedling establishment (regardless of scarification timing) because of drought. We conclude that the optimum timing of soil scarification for regenerating Scots pine in central Sweden is before the seed fall begins, from autumn through to mid-April (early spring).