Dominance by annual plants has traditionally been considered a brief early stage of ecological succession preceding inevitable dominance by competitive perennials . A more recent, alternative view suggests that interactions between annuals and perennials can result in priority effects, causing annual dominance to persist  if they are initially more common. Such priority effects would complicate restoration of native perennial grasslands that have been invaded by exotic annuals. However, the conditions under which these priority effects occur remain unknown. Using a simple simulation model, we show that long-term ( 500 years ) priority effects are possible as long as the plants have low fecundity and show an establishment-longevity tradeoff, with annuals having competitive advantage over perennial seedlings. We also show that short-term (up to 50 years ) priority effects arise solely due to low fitness difference in cases where perennials dominate in the long term. These results provide a theoretical basis for predicting when restoration of annual-invaded grasslands requires active removal of annuals and timely reintroduction of perennials.
Dominance by annual plants has traditionally been considered a brief early stage of ecological succession preceding inevitable dominance by competitive perennial plants . A more recent, alternative view suggests that interactions between annuals and perennials can result in priority effects, causing annual dominance to persist for decades if they are initially more common. Such priority effects would complicate restoration of native perennial grasslands that have been invaded by exotic annuals. However, the conditions under which these priority effects occur remain unknown. Using a simple simulation model, we show that long-term ( equilibrium ) priority effects are possible only when the plants have low fecundity and show an establishment-longevity tradeoff, with annuals having competitive advantage over perennial seedlings. However, transient (but long-lasting over decades ) priority effects are more likely and does not require the tradeoff. Our results provide a theoretical basis for predicting when restoration of annual-invaded grasslands requires active removal of annuals and timely reintroduction of perennials.
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for decades
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500 years
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We also show that short-term (up to 50 years
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arise solely due to low fitness difference in cases where perennials dominate in the long term. These
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