Root Architecture of Jarrah (Eucalyptus marginata) Trees in Relation to Post-Mining Deep Ripping in Western Australia

This research aimed to investigate coarse root systems of Jarrah (Eucalyptus marginata Donn ex Sm.) trees at a 13-year-old restored bauxite mine site in south-western Australia. Excavations in an area with small trees (low-quality site) revealed that deep ripping equipment failed to penetrate the cemented lateritic subsoil, restricting coarse roots (roots > 5 nun in diameter) to the top 0.5 m of the soil profile, resulting in fewer (1,344 stems/ha) and smaller (mean height 4.5 m) Jarrah trees. An adjacent area within the same pit (high-quality site), with a stand density of 3,256 stems/ha and a mean height of 8.0 m, had a kaolinitic clay subsoil which coarse roots penetrated to the average ripping depth (1.5 m). Trees at the low-quality site did not penetrate the subsoil with their taproot, relying instead on a large number of lateral (5.3-8.0/tree) and sinker (12.0-16.5/tree) roots. Taproots of trees on crests at the high-quality site also did not penetrate the subsoil, and in contrast to trees at the low-quality site, they produced fewer lateral and sinker roots (2.3 and 2.0/tree, respectively). Taproots of trees in riplines at the high-quality site directly penetrated the ripline and these trees also produced fewer lateral and sinker roots (5.0 and 3.7/ tree, respectively) than those at the low-quality site. Jarrah trees appear to have opportunistic root systems capable of responding to a variety of soil conditions encountered in the post-mining landscape.