Testing the growth limitation hypothesis for subarctic Scots pine

P>1. We tested if tree line trees are sink or resource limited by comparing the reactions in Scots pine trees (Pinus sylvestris L.) to changes in resource availability (through nutrient addition and defoliation), and in sink strength (through debudding) in north-eastern Finland. 2. Height extension growth increased by over 200% and shoot extension growth by 27%, as a result of nutrient addition, whereas changes in radial increment were smaller and not statistically significant. 3. Although in defoliated trees height and shoot extension were not significantly affected, defoliated trees decreased their radial growth by 50%. 4. Branch extension growth of the remaining buds was increased due to debudding treatment by 47%, but there were no changes in radial increment. 5. Non-structural carbohydrate concentrations in twigs, however, remained relatively constant in all treatments. 6. There were no statistically significant changes in carbon isotope ratio due to any of the treatments, indicating that the manipulation treatments did not modify tree water relations. 7. Synthesis. Our results do not support the growth limitation theory for tree line trees and suggest that resource limitations might be more important.