Nutrient status of Norway spruce stands subjected to different levels of overstorey removal

Foliage nutrient concentrations of overstorey and understorey Norway spruce [Picea abies (L.) Karst.], and height growth and needle weights of understorey saplings, were studied in a 7-year period after harvest. The following treatments were applied on each of three sites 5 years prior to needle sampling: control with no cutting, partial cutting with 50-60% removal of basal area, and patch cut (25x25 m-0.063 ha clear-cut). Saplings on control plots had higher concentrations of K and Cu in current-year needles (C) than overstorey trees. Increased harvest intensity led to a reduction of K in C needles and Mg in (C+1) needles of saplings, and of B in both saplings (C, C+1) and overstorey trees (C+1). Sapling needle weights generally increased with harvest intensity, whereas no effect of foliage N status on needle weights could be detected. The growth response of saplings was explained by the interaction between foliage N status, quantified as average N concentration in C and (C+1) needles, and harvest intensity. The results illustrate that sufficient N supply is a key factor for the ability of advance regeneration to utilise the improved light condition associated with overstorey removal.