Is burning a standing population of invasive legumes a viable control method? Effects of a wildfire on an Acacia mearnsii population
Acacia mearnsii is an important invasive plant in most of the higher rainfall areas in South Africa. The production of long-lived water-impermeable seeds results in the establishment of large soil-stored seed banks. One way of controlling these seed banks is by felling the plants and burning them to destroy or to stimulate seeds to germinate, so that the resulting seedlings may be controlled. In order to save costs, the hypothesis that the plant population can be burned without felling beforehand, was investigated. A wildfire that swept through a standing population of A. mearnsii plants provided an opportunity to investigate the effects on the population. The mortality of the pre-fire population, the subsequent establishment of seedlings, mortality of seedlings and the spread of the population after the fire were investigated. It was found that the above-ground population increased by a factor of ca. 21,8 due to coppicing of young plants and the mean distance of spread from the edge of an infestation was ca. 20 m. About 90 % of seedlings that established, died within two years. Due to the growth of the population, and the difficulty of controlling coppicing plants, a standing burn is not recommended as a control measure for A. mearnsii.