Managing beyond the invader: manipulating disturbance of natives simplifies control efforts

Abstract

# Invasive plants have negative impacts on ecosystems worldwide. Several ecological studies have identified disturbance as a causative mechanism of plant invasions. Changes to natural disturbances and/or newly imposed disturbances can favour an invader over native species especially those that are better adapted to prior conditions. # 2. To link the disturbance ecology of invasives to their management, we investigated the benefit of incorporating actions that manipulate disturbance (natural or imposed) into control efforts. We developed a simple model that describes the dynamics of an invader whose establishment is preferentially favoured by disturbance. # 3. The model includes the probability of disturbance differentially affecting sites occupied by natives and invaders. Invaded sites are disturbed by alternative control measures, which act to kill and/or remove above-ground biomass and reduce the seed bank. We couched the model in a decision theory tool, stochastic dynamic programming, and applied it to the management of Mimosa pigra, a pan-tropical invasive perennial shrub. # 4. We found that targeting the above-ground biomass of the invader (current population) was optimal when the probability of disturbance of native sites and the invader seed bank size were low to moderate. When both the rate of disturbance of native sites and invader seed banks were high, the best measure was that with the highest probability of reducing the seed bank (future populations). This measure was optimal despite its trade-off of having the highest probability of reinvasion. # 5. Synthesis and applications. Manipulation of disturbance regimes in both native and invaded sites can simplify control efforts. If there is a high probability that native vegetation will be disturbed, then management efforts should focus on future populations by attempting to reduce the size of the invader seed bank. This complicates control, as seed bank size is difficult to measure and reducing it requires intensive actions, which are likely to also negatively affect the seed bank of native species. If, however, the probability of disturbance of native sites can be reduced, practitioners can shift control from future populations to the current population, which is more straightforward to implement and monitor