Identifying the mechanisms by which invasive species outcompete native species is currently limited by the lack of information regarding species interactions between invaders and native plants. Invaders may successfully colonize either because they have a consistent advantage over native species or because they are capable of outcompeting the community dominants. We used a greenhouse experiment to test whether Lespedeza cuneata (sericea) has a competitive advantage over sixteen native species representing three functional groups (grass, legume, or forb) typically found in the grasslands where L. cuneata is invasive. Each native species was grown with a conspecific, the invader (L. cuneata), or a native congener (Lespedeza capitata).
Results/Conclusions
In general, L. cuneata had effects on the growth of sixteen native species that were similar to or in some cases stronger than those exhibited by the native Lespedeza. The responses of native species tended to vary by functional group. Lespedeza cuneata reduced growth of forbs in comparison to the presence of a conspecific while grasses appeared to have increased biomass in the presence of the invasive legume. Although the effects of the invader on grasses and legumes were similar, the pattern for legumes was highly variable suggesting a greater diversity of either competitive strategies or abilities in this functional group. Although the effects of L. cuneata on natives was modest, the response of L. cuneata was generally higher in the presence of native species than when grown with a conspecific and this response was larger than that exhibited by L. capitata. Consequently, the competitive advantage of L. cuneata may be due to increased growth rates in the invaded range rather than through suppressive effects on the native species.