Wood density and tracheid properties of Scots pine: responses to repeated fertilization and timing of the first commercial thinning

The aim of this study was to compare the effects of fertilization and thinning on the growth rate and wood and tracheid properties of Scots pine (Pinus sylvestris L.) in southern Finland. The study was based on two long-term experiments with two fertilization treatments (unfertilized and 150 kg N ha21 every 5 years) and two thinning levels (delayed and intensive first commercial thinning) in a randomized block design. A total of 80 trees were sampled30yearsafter theonsetof the treatments. Intensive thinningenhancedthe radial growthof the remain-ing trees by 52 per cent comparedwith the delayed first thinning. Accordingly, the fertilization increased the radial growth by 37 per cent compared with the unfertilized trees. However, only small differences were found between the treatments in the earlywood/latewood ratio (3–9 per cent), wood density (2–8 per cent), tracheid diameter (2–5 per cent), cell wall thickness (0–10 per cent) and tracheid length (4–5 per cent). The results demonstrated that the prevailing fertilization and thinning treatments of Scots pine stands considerably enhance the growth rate but do not cause major detrimental changes in the wood and tracheid properties