Invasive plants are often removed without plans for follow-up management, be it further clearing or active restoration. However, most ecosystems have multiple rather than single plant invaders, which can lead to one species taking over after another is removed. There is a need for general principles regarding invader interactions across varying environmental conditions, so that secondary invasions can be predicted, and managers can allocate resources towards pre-treatment or post-removal actions. By reviewing removal experiments conducted in three Hawaiian ecosystems, we evaluate the roles of environmental harshness, priority effects, productivity potential, and species interactions in influencing secondary invasions. We generate a conceptual model with a “surprise index” to describe whether long-term plant invader composition and dominance is predictable versus stochastic after a system perturbation. Under extremely low resource availability, the surprise index is low, while under intermediate-level resource environments, invader dominance is more stochastic, and the surprise index is high. At high resource levels, the surprise index is intermediate: invaders are likely abundant in the environment, but their response to a perturbation is more predictable than at intermediate resource levels. We suggest further testing across environmental gradients to determine key variables that dictate the predictability of post-removal, invader composition.
Audio/Video, Conference Presentation, SER2019
Society for Ecological Restoration