Vertical structure of Scots pine crowns in different age and size classes

The pipe model theory postulates a static relationship between foliage mass /area and the cross-sectional area of active pipes in branches and stems. I f a regular relationship exists, the theory can be used for modelling growt h allocation within crowns, provided that the turnover of active pipes and foliage is understood. The objective of this study was to assess to what ex tent the assumptions of the pipe model hold true within the crowns of 24 Sc ots pine sample trees of different age and social position. The results sug gest that Scots pine crowns are very regular, but some important modificati ons to the pipe model assumptions are required. The relative vertical folia ge density distribution peaked at about 50% down the live crown regardless of age or social position. The ratio of foliage mass to branch cross-sectio nal area in the top half of the crown increased from the top downwards. The ratio of cumulative branch cross-sectional area to stem cross-sectional ar ea in the top half seemed to increase with tree vigour or growth rate. The ratio of foliage mass to branch cross-sectional area decreased fast in the lower half of the crown, and this decrease was faster than could be predict ed from heartwood formation in the branches. This result may be taken as (1 ) evidence against the pipe model, or as (2) an indication that active pipe s cannot always be identified with sapwood. The latter proposition should b e studied further.