Taper and heartwood in roots and tree stability

Summary

Measurements of diameter of eucalypt roots (exposed by wave action following dam construction) indicate that roots normally taper only at forks and near the stem where they are subject to mechanical stresses due to tree sway. Published data indicate that the taper, i.e. the extra thickening of proximal portions of tree roots, is a response to tree sway. This thickening enables trees to adapt to and remain upright in widely varying soil and terrain conditions. Protection of trees from swaying may put them at risk of stem or root failure when the protection is reduced.

Limited observations on several tree genera and some literature suggest that heartwood formation in roots is normally confined to the tapering proximal portions of the roots. This is consistent with the suggestion that wood added for mechanical support is in effect converted to heartwood because it is in excess of needs for conduction and storage.