Fertilization and release cutting increase seed production and stem diameter growth in Pinus sylvestris seed trees

The effects of fertilization (with nitrogen, phosphorus, potassium, sulphur, magnesium and boron) and release cutting, both separately and combined, on seed production and stem growth were investigated using a two-level factorial design in 160 individually treated Scots pine (Pinus sylvestris L.) seed trees over 5 years at a low-productivity site in central Sweden. The effects of the treatments on mineral nutrient levels in the needles and the correlations between these levels and seed production were also investigated. Release cutting significantly increased the seed production after both 3 and 5 years, while fertilization increased the seed production after 5 years but not after 3 years. Compared with control trees, released trees increased their diameter growth by more than 300% and fertilized trees by about 160%. Release cutting and fertilization increased the availability of nitrogen, phosphorus and potassium for the seed trees. Hence, both released and fertilized trees had significantly higher needle dry weights, 1000-seed weights and needle nutrient levels than control trees 3 years after the treatments. However, 5 years after the treatments these effects had greatly diminished, indicating that most of the increased amounts of nutrients had been consumed by then