Controlling the seed bank of the invasive plant Acacia saligna: comparison of the efficacy of prescribed burning, soil solarization, and their combination

Reducing the seed bank of invasive plants is a prerequisite for successful restoration of invaded ecosystems. The Australian legume tree Acacia saligna is one of the worst invasive plants in Mediterranean climate regions. This fire-adapted species possesses a large persistent seed bank characterized by physical dormant seeds. The present research was aimed to compare the efficacy of prescribed burning, soil solarization by solar heating of moist soil, and their use in combination on A. saligna seed bank reduction, using the buried seed method, and on seedling emergence from the natural seed bank, as a model of controlling fire-adapted plants. The data obtained show that the direct effect of prescribed burning on the buried seed dynamics was highly variable, and it only reduced seed viability from 98% to about 56%. Soil solarization, particularly in combination with prescribed burning, was much more effective than prescribed burning alone, reducing seed viability to about 29 and 4%, respectively. These results were confirmed by recording seedling emergence from the natural seed bank during two successive germination years following the treatments. Only a relatively very small number of seedlings emerged in the soil solarization treatment and none in the combined treatment. Based on the above data, it is recommended to apply prescribed burning as a pretreatment for soil solarization, or to utilize wild fires followed by soil solarization to reduce the seed bank of invasive fire-adapted plants. In situations in which fire cannot be used as a pretreatment, soil solarization alone is reasonably effective.