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 mm 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.