Nutrient status in needles of Norway spruce and Scots pine following harvesting of logging residues

Nutrient concentrations in current and 1-year old needles from two Picea ab ies (L.) Karst and two Pinus sylvestris L. stands in Sweden were determined 8-10, 16-18 and 22-24 years after clear-felling and experimental manipulat ion of harvesting intensity. On all sites, three levels of harvest intensit y had been applied in a randomized block design (n=4); (i) conventional ste m-only harvesting, where all logging residues (i.e. tops, branches and need les) were evenly distributed on the ground, (ii) harvesting all above-groun d tree parts except needles and (iii) above-ground whole-tree harvesting (n o residues left on site). At stand age 8-10 years, nitrogen concentrations in the current year needles in plots where all residues or needles only wer e retained were higher than in whole-tree harvested plots, whereas concentr ations of K, Ca and Mg were lower. The latter response was interpreted as a dilution effect. P:N, K:N, Ca:N, Mg:N, Mn:N and Zn:N were in general highe r after whole-tree harvesting treatments than after the treatments where al l residues or only needles had been left on site. At stand age 16-18 years, no significant differences in nitrogen concentrations were observed betwee n treatments, but the levels of Ca, Mg and Mn in both current and 1-year-ol d needles were lower after whole-tree harvesting than after the treatments where logging residues remained on site. By contrast, potassium levels in t he foliage were highest in treatments where only the needles were left on s ite, whereas the lowest levels were observed for treatments where all resid ues was left. At stand age 22-24 years, the treatment effects had diminishe d, except for the effects on Ca and K on the southern Norway spruce stand. It is concluded that the nutrient release from logging residues enhances nu trient uptake in trees of the succeeding forest generation, but this effect does not occur simultaneously for all elements.