The adaptation of the compression strength of hardwood branches to the loading caused by gravity

Branches are permanently loaded by their weight and there is temporarily ad ded the weight of the leaves or snow. Hence bending stresses result which c ause tension in the wood of the upper side of the branches and compression in the under-side. Measurements of the compression strength of hardwood bra nches show that the strength is adapted to the load. At the compression loa ded underside was measured a higher averaged compression strength than at t he upper side. Comparisons with the compression strength in trunks show tha t this is an optimization and that it is not only caused by reduced strengt h of the tension wood in the upper side of the branches. This increase of c ompression strength is probably caused by the thicker lignified cell layers of the wood in the under-side. The width of annual rings seems not to be r elevant for the compression strength in branches.