Leaf/sapwood area ratios in Scots pine show acclimation across Europe

We tested the hypothesis that leaf/sapwood area ratios (S) in Scots pine (Pinus sylvestris L.) differ across Europe. Data from published records were collected and critically reviewed, and five new sites were studied to increase the overall sample size available for analyses. For seven studies for which data were available, we also determined the magnitude of the errors resulting from the use of ratio and regressiontype estimators during subsampling for leaf areas of individual trees. These subsampling errors were then compared with those resulting from least square regressions of leaf area against sapwood area, and the total error was determined. Finally, correlation analysis was used to test for significant relationships between S and site-specific and stand-specific variables. Subsampling for leaf area resulted in errors, the magnitude of which was site specific and depended on sampling sizes and protocols. In general, despite larger total errors resulting from accounting for subsampling, significant differences were found among S, both at breast height and at the base of the living crown, at least for the most extreme cases. Significant negative relationships were found between S and summer vapour pressure deficit and maximum summer temperature. Although preliminary, our results confirm previous suggestions about climatic effects on Scots pine leaf/sapwood area ratios by enlarging the analysis to a wider range of European sites and by including genetic variability across stands.