The influence of compaction and soil strength on the establishment of four Australian landscape trees

Abstract

Two experiments were conducted to test the hypothesis that trees able to establish in urban soils will have a higher-than-average tolerance to the higher mechanical impedance and soil strength of compacted soils. Experiment 1 tested the ability of the roots of Corymbia maculata (spotted gum, syn. Eucalyptus maculata), Lophostemon confertus (brush box), Corymbia ficifolia (red flowering gum, syn. Eucalyptus ficifolia), and Agonis flexuosa (willow myrtle) seedlings to penetrate a sandy loam soil compacted to bulk densities of 1.4 and 1.8 mg · m-3 at 13% gravimetric moisture content. While roots of all species were able to penetrate the soil at the higher bulk density, total root penetration depth was reduced by 60% in all four species. Experiment 2 tested the ability of Corymbia maculata and C. ficifolia to penetrate soil compacted at bulk densities 1.4, 1.6, and 1.8 mg · m-3 at two moisture levels, 7% and 10% gravimetric moisture. At 7% moisture, both species were able to penetrate soil compacted to 1.4 and 1.6 mg · m-3, but neither species was able to successfully penetrate soil compacted to 1.8 mg · m-3. At 10% moisture, both species were able to penetrate soil compacted to 1.4 and 1.6 mg · m-3. They also were able to successfully penetrate soil compacted to 1.8 mg · m-3, although with significantly less depth of penetration than at the two lower bulk densities.