Twelve-year growth response of Scots pine to thinning and nitrogen fertilisation

Effects of thinning and nitrogen fertilisation, singly and in combination, on growth of 56-year-old Scots pine ( Pinus sylvestris L.) trees in northern Sweden were examined for the 12 years after treatment. The response to treatments was measured as dry weight biomass change in above and below ground components over the 12 years and as four-year period changes in relative radial, height, and volume growth under bark. Results were expressed in terms of average tree and as a stand total. During the 12-year period following treatment, biomass production per tree was increased in all fractions by thinning, but only for shoot axes and crown biomass by fertilisation. In the first four-year period after treatment both thinning and fertilisation gave a positive response in radial and volume growth. The response to fertilisation in radial and volume growth faded out after eight years, although a positive effect after thinning could still be seen after 12 years. Height growth was not affected by treatments. In comparison to the control, volume production per hectare decreased by 37% after thinning singly, 10% after the combined treatment, and increased by 20% after fertilisation. The results are discussed in terms of nitrogen availability, light competition, and needle efficiency.