Wpływ przerzedzenia okapu górnego na rozwój podrostów sosny zwyczajnej (Pinus sylvestris L.) w pogradacyjnych drzewostanach w Lasach Pilskich

In the paper the density, height, diameter, slenderness and vitality of the 17 year−old pine young−growth stands depending on the basal area of the shelterwood (four thinning variants: G1−G4). The studies were carried out in eleven 70−90 year−old pine stands heavily damaged in the 80s of the past century by the nun moth (Lymantria monacha L.). With the development of the overstorey the growth, the vitality and the stability of young stands declined. In addition, a decrease in the survival of the young−growth stands under the dense canopy (variant G4) was recorded. A long−term maintenance of young stands under the shelter of the canopy in the areas of low annual precipitation (below 600 mm) requires the reduction of the dbh basal area to the level of at least 15 m3/ha before attaining the age of 15 years.