Emergence and control of gorse seedlings after the 2017 Port Hills fire

Abstract

An experiment on the Port Hills, Canterbury, after mature gorse was burnt in the fires of February 2017, showed an oversown Italian ryegrass mix out-competed the rapidly germinating gorse seedlings. The shaded gorse seedling population reached a peak of 680 plants/m² in June, declining to ~450 plants/m² in October compared with >600 plants/m² in the unshaded plots. As soil moisture dropped in summer, the gorse seedling population decreased to 10 plants/m² by March 2018, compared with 73 plants/m² in the unshaded plots. Gorse seedlings that had been shaded by Italian ryegrass had shorter roots and lower dry weights than those grown without competition. The oversown mix was more successful on the south than north-facing slope where more bare ground enabled patches of gorse to re-establish. The oversowing of Italian ryegrass was shown to be a viable option to control gorse particularly after an unplanned burn that removed the fences and water supply.