Before revision:  However, circumstantial evidence suggests that annual-perennial interactions can cause priority effects, allowing persistent annual dominance when annuals are initially more common than perennials. The necessary conditions for these potential priority effects remain unknown despite the extensive effort devoted to restoration of native perennial dominance in systems invaded by exotic annuals.
After revision:  However, circumstantial evidence suggests that annual-perennial interactions can cause priority effects, allowing persistent annual dominance when annuals are initially more common . Such priority effects would complicate restoration of native perennial dominance in systems invaded by exotic annuals.