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.