Fire as a Management Tool for a Tropical Woody Weed: Mimosa pigra in Northern Australia

The use of fire for managing infestations of the invasive tropical shrub Mimosa pigra was investigated in a field experiment and with small-scale fires in containers. In the field experiment, gelled gasoline was applied to thickets of mimosa from a helicopter. When applied in a spiral pattern, the fire became intense and self-propagating, clearing the thicket completely. When applied along a straight line, the fire quickly burnt out and failed to destroy the stand. Seeds exposed to fire in the field, and in containers, died or became germinable. Deaths were most common at the soil surface, while enhanced germination occurred below the surface, down to a depth of 5 cm, but no deeper. Fire may therefore be used, both on small and large scales, to deplete that seed bank of mimosa by killing or germinating a large proportion of the seeds, allowing their simultaneous treatment with herbicides. Because a proportion of seeds may remain at depths greater than 5 cm, however, follow-up control must be practised.