The subsequent diagram shows steady-state water potential profiles along chosen branch pathways in different tree crowns, obtained with the numerical simulation model HYDRA. The top diagram was taken from a 15-year-old Norway spruce which was generated with GROGRA from the growth grammar epi2.lsy and is depicted on the right-hand side. The central part shows the diagram and graphical view of a 12-year-old Norway spruce which was completely mapped by G. Anzola Jürgenson and reconstructed as a virtual tree with GROGRA. The bottom diagram was derived from a Thuja occidentalis tree mapped by Tyree (1988). The positions in the diagrams marked by arrows correspond to the treetops. For the profiles, the trunk and at least twenty first-order axes which branch off at approximately equal distances were chosen. Path length of profile points is measured as distance from the base of the trunk. Marked differences in the hydraulic patterns between the Thuja and the Piceas appear. HYDRA can also calculate time series of water potential and flow in the virtual trees (not shown).

(From Thomas Früh & Winfried Kurth, The hydraulic system of trees: Theoretical framework and numerical simulation, J. Theor. Biol., 201 (1999), 251-270. [gzipped Postscript file, 1.7 MB (unzipped: 4.5 MB)].)

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