Priority effects: Emerging principles for invasive plant species management

International audienceMany anthropic activities generate soil disturbances, favoring competitive, fast growing invasive plant species at the expense of natives. Active restoration of invasion-resistant plant communities is increasingly recognized as a relevant strategy to combat invasive plant colonization in disturbed areas, but results are often unsatisfying. Historical effects, referred as “priority effects” (i.e. the effects generated by the order in which species arrive at a local site), can have a major role in community assembly and invasion success because they involve early colonists altering the performance of later colonists. Taking these priority effects into account in restoration projects is emerging as a relevant way to improve native species restoration success and prevent invasion. The present review discusses two strategies considering priority effects that would help to achieve the classic restoration goal of “more natives, less invasives”. The first strategy relies on tackling priority effects of invasive plants using different management options adapted to local environmental conditions, including removal, reduction of propagule sources, or mitigation of soil legacies. Indeed, invasive plants often generate strong priority effects providing themselves a substantial competitive advantage through early emergence and quick growth, but also self-induced soil modifications that can persist after their removal or death, commonly termed “soil legacies”. In fertile and stable conditions, the reduction of invasive species priority effects must be coupled with the restoration of an invasion-resistant native plant cover to avoid reinvasion and secondary invasions. The second strategy is to bring about situations in which the restored native species are more likely to exert strong priority effects, decreasing invasion success. For this purpose, we sketch possible options open to restorationists based on resource or non-resource mechanisms. First, we discuss ways to maximize resource preemption by extending the time advance given to restored native species and manipulating restored species characteristics. Second, we consider the potential effect of increasing niche overlap between native and invasive species. Third, we introduce the potential manipulations of non-resource mechanisms, such as allelopathy, herbivory, disease, or the presence of mycorrhizae, to increase priority effects. This review incorporates recent research on priority effects to draw the outlines of priority effects-based restoration strategies and define future research questions that need to be addressed to test and improve these strategie