Mineral nutrients in needles of Pinus sylvestris seed trees after release cutting and their correlations with cone production and seed weight

Abstract

The effect of release cutting on seed production was investigated in six Scots pine ( Pinus sylvestris L.) seed tree stands and four unreleased stands (forests) in central Sweden. The study was restricted to the uppermost 2 m of the tree crowns. Correlations were analysed between concentrations of nutrient elements in the needles, seed characteristics and numbers of conelets. The mean number of conelets was ca. 65% higher in released seed trees than in control trees in unreleased stands. The mean 1000-seed weight was about 15% higher in the released trees, while the mean percentage of viable seeds was lower in released trees (94%) compared to control trees (98%). However, the number of viable seeds per cone was not significantly different between released and unreleased trees. The concentration of nitrogen, potassium, and phosphorus in needles was ca. 23, 10, and 13% higher, respectively, in released trees. The mean needle dry weight was 20% higher. Nitrogen, potassium and phosphorus concentrations in needles were significantly positively correlated to numbers of conelets as well as to mean 1000-seed weight. None of the other analysed mineral nutrients were significantly correlated to seed production. The mean needle dry weight was significantly positively correlated to the number of conelets, but not to the mean 1000-seed weight. Our conclusion is that improved nutrient status in the seed trees is an important factor explaining the increase in seed production that occurs after release cutting.