Structural adaptation rather than water conservation was observed in Scots pine over a range of wet to dry climates.

We investigated the functional and structural responses of Scots pine to climate and estimated the importance of the genotype on the traits studied. We analysed 13C isotope discrimination (Δ13C) of various provenances in a common garden experiment and gas exchange characteristics for provenances growing in their natural environment. No clear climatic trend was found in the foliar Δ13C values of common garden trees. Similar results were obtained from estimation of λ (a largely VPD, temperature and light independent measure of intrinsic water use efficiency) from the gas exchange data. The ratio of needle mass to unit stem area and branch area to stem area increased towards south in both experiments and hence, seemed to be genetic. Trees from drier and warmer conditions seemed not to have either lower needle mass or higher intrinsic water use efficiency compared to northern latitudes.

Evaporative demand determines branchiness of Scots pine.

Analysis of the branch area/stem area ratio of Scots pine growing in different climatic conditions in Europe and Siberia indicates that the branch area supported by a stem increases in warmer and drier conditions. The ratio was significantly correlated with several climatic variables, especially with potential evapotranspiration (E p). The ratio was negatively correlated with stand density (d s). A regression model combining E p and d s accounted for 85% of the total variation. These trends are believed to reflect hydraulic segmentation of trees and may represent a strategy to avoid cavitation in the tree, especially in the branches.