Foliage area–sapwood area relationships of Scots pine (Pinussylvestris) trees in different climates

Abstract

Foliage mass and wood cross-sectional area were measured at different points of branches and stems within the living crown of Scots pine (Pinussylvestris L.) trees from sample plots, representing wide geographical variation. The measurements were taken during the period of annual minimum foliage mass. The needle mass: branch cross-sectional area ratio, measured below the lowest living whorl of sub-branches, differed among measured points and was normally lower for the uppermost branches, but also decreased in the lower canopy. The decrease at the lower canopy was hypothesized to reflect an excess water transport capacity resulting from the senesced needles. The lower ratio in the uppermost branches might be explained by M.H. Zimmermann's hypothesis that the water supply of foliage close to the stem is preferred. A similar trend in the branch area: stem area ratio was observed along the stem. There seemed to be strong geographic variation in the ratio between the total cross-sectional area of branches of the crown measured and the stem cross-sectional area below the living crown. The branch area: stem area ratio was higher in the southern stands, whereas there was no clear trend for the needle area: branch area ratio. The results are discussed in relation to the hydraulic architecture of trees.