Tree mechanics, hydraulics and needle-mass distribution as a possible basis for explaining the dynamics of stem morphology

2001

S. 241-254

9 Abb., 1 Tab., 12. Lit. Ang.

Unselbständiges Werk

200087242

Früherer Titel: Lesnictvi - Forestry

The aim of the presented work is to verify existing hypotheses which explain the control of secondary growth in diameter. Approaches which try basically to describe stem growth can be grouped into those pertaining to mechanics, hydraulics and the needle-mass distribution of the tree. It is very probable that a mechanical stress on cambial cells, due to stem bending by wind forces, is one of the central triggers for diameter growth. Simulation using an elasto-mechanical model of a 64-year old Douglas fir tree show that the "constant stress hypothesis" is not valid and that a "stress-controlled adaptive growth" cannot be regarded as a universal rule. The basic idea of the pipe model theory, the assumed constancy of the relation between the sapwood cross-sectional area and the needle mass above, turned out to be wrong. But equal tendencies for all investigated trees could indicate approaches for a modified hypothesis. Relations between the spatial needle-mass distribution and thus, the supply of assimilates and the spatial distribution of annual area growth along the stem seem to exist, but are not quite clear. Most probably, all three influences are superimposed, but the stress- or strain-controlled adaptive growth is assumed to dominate, with the exception of the crown, where requirements of water supply probably take over the control of diameter growth.