Role of priority effects in invasive plant species management: Early arrival of native seeds guarantees the containment of invasion by Giant ragweed.

Abstract

Empirical evidence shows that early arrival of native species, which induces the priority effects, can contribute to invasive plant species containment. However, more systematic studies are required to test the applied relevance of the priority effect. This study therefore aimed at testing the priority effects generated by different sowing times of seeds of nine native species on one target invasive plant species, that is, Giant ragweed (Ambrosia trifida). This study hypothesized that, when sown earlier, some native species will be able to substantially contain A. trifida through resource preemption. An additive competition design was used to test the competitive effects of native species on A. trifida. Depending on the sowing times of native and invasive plant species, three priority treatments were conducted: all species sown at the same time (T1); native species sown 3 weeks before A. trifida (T2); and native species sown 6 weeks before A. trifida (T3). Priority effects created by all nine native species significantly affected the invasibility of A. trifida. The average value of the relative competition index (RCIavg) of A. trifida was the highest when native seeds were sown 6 weeks early and decreased with decreasing early sowing time of native plants. The species identity effect was not significant on RCIavg if natives were sown at the same time or 3 weeks earlier than A. trifida invasion, but it was significant (p=.0123) if they were sown 6 weeks earlier than A. trifida. Synthesis and applications. The findings of this study clearly show that native species, when sown early, provide strong competition and resist invasion through prior utilization of resources. The consideration of this knowledge might improve A. trifida invasion management practices.