Invasion, competitive dominance, and resource use by exotic and native California grassland species

Abstract

The dynamics of invasive species may depend on their abilities to compete for resources and exploit disturbances relative to the abilities of native species. We test this hypothesis and explore its implications for the restoration of native ecosystems in one of the most dramatic ecological invasions worldwide, the replacement of native perennial grasses by exotic annual grasses and forbs in 9.2 million hectares of California grasslands. The long-term persistence of these exotic annuals has been thought to imply that the exotics are superior competitors. However, seed-addition experiments in a southern California grassland revealed that native perennial species, which had lower requirements for deep soil water, soil nitrate, and light, were strong competitors, and they markedly depressed the abundance and fecundity of exotic annuals after overcoming recruitment limitations. Native species reinvaded exotic grasslands across experimentally imposed nitrogen, water, and disturbance gradients. Thus, exotic annuals are not superior competitors but rather may dominate because of prior disturbance and the low dispersal abilities and extreme current rarity of native perennials. If our results prove to be general, it may be feasible to restore native California grassland flora to at least parts of its former range.

Pathogen-induced reversal of native dominance in a grassland community

“…Paradoxically, recent empirical work demonstrates that the invasive annual grasses in California are inferior competitors for resources shared with the native perennials (10,11), supporting earlier theoretical insights into annual-perennial competition (12). Thus, mechanisms other than exploitative competition were necessary to drive the invasion of this system by competitively inferior annual grasses.…”

Characteristics of Successful Alien Plants

“…However, most of them focussed on extrinsic factors, such as disturbance and species richness, rather than on intrinsic species traits (Robinson et al 1995;Naeem et al 2000;Seabloom et al 2003;Maron et al 2013). Moreover, most of these studies introduced only one or few species, which precludes comparisons of characteristics associated with establishment success.…”

Non-Native Plants Disrupt Dual Promotion of Native Alpha and Beta Diversity

“…2a), suggests competitive exclusion of native species by non-native species (Seabloom et al 2003). Possible mechanisms of competitive exclusion include reduced sites available for germination (Walker et al 2003) and limiting access to water, nutrients or both (Stubbs and Wilson 2004;Bartelheimer et al 2010;Everard et al 2010).…”