Dominance by annual species is commonly viewed as a transient state in plant succession preceding eventual perennial dominance . 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.  Using a simple simulation model, we show that long-term (500 years) priority effects in annual-perennial interactions are possible as long as the plants have low fecundity and show a competition-longevity tradeoffsuch that annuals are more competitive than perennial seedlings. Short-term (up to 50 years) priority effects are even more likely: they do not require a competition-longevity tradeoff and can arise solely by low fitness differences . These results question the traditional view of annual dominance as a short-lived transient state and suggest that conditions for priority effects must be understood to achieve successful restoration of perennial dominance .
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 .
R
species is commonly viewed as a transient state in plant succession preceding eventual perennial dominance . However, circumstantial evidence suggests that annual-perennial interactions can cause
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
R
allowing persistent annual dominance when annuals
causing annual dominance to persist if they
R
than perennials. The necessary conditions for these potential priority effects remain unknown despite the extensive effort devoted to
. Such priority effects would complicate
R
dominance in systems
grasslands that have been
A
However, the conditions under which these priority effects occur remain unknown.
D
in annual-perennial interactions
R
a competition-longevity tradeoffsuch that annuals are more competitive than
an establishment-longevity tradeoff, with annuals having competitive advantage over
R
Short-term
We also show that short-term
R
are even more likely: they do not require a competition-longevity tradeoff and can arise solely by low fitness differences
arise solely due to low fitness difference in cases where perennials dominate in the long term
R
question the traditional view of annual dominance as a short-lived transient state and suggest that conditions for priority effects must be understood to achieve successful restoration of perennial dominance
provide a theoretical basis for predicting when restoration of annual-invaded grasslands requires active removal of annuals and timely reintroduction of perennials