If curved structural parts of a tree are straightened by bending lateral fo
rces would lead to longitudinal splitting if the internal structure of the
wood would not be optimized and load-adapted.
For the example of a leaning beech tree (F. sylvatica L.) different ways of
internal self-optimization are shown which allow the tree to live with lat
eral forces without failure:
1. Radial rays act like tensile ropes growing larger in cross-section towar
ds the bark and finally may even split into many smaller rays.
2. The late wood of the individual tree rings acts as an anchor-plate behin
d the ,,knots" of the rays.
3. By inserting secondary rays in between primary rays their distance in ci
rcumferential direction will be limited.
4. The brittle-stiff late wood bridges in between two rays are curved into
the shape of a bow with the convex side to the tree center. This is to bett
er resist the radial forces pushing the tension wood fibres against the lat
e wood bridges (Fig. 5). It compares to the tensile stress release of old b
ridges. Also the knots made up by the blade-sheath-connections of the rays
act like compressive wedges and compensate the circumferential tensile forc
es due to bending of the late wood bridges.
5. The ray of beeches itself has optimized weldings at the transition from
late to early wood. This done by inserting the blade of the early wood ray
into the sheath of the stiff hollow late wood ray. Both are glued together
by pectin.
Regarding all this one has one more reason to believe that trees with small
rays provide less public safety in cities than trees with large multi-seri
ate rays.