Can native annual forbs reduce Bromus tectorum biomass and indirectly facilitate establishment of a native perennial grass?

Abstract

Restoration is challenging in systems invaded by competitive, disturbance oriented plants, but greater success may be achieved by mimicking natural successional processes and including disturbance-oriented natives in a seed mix. We asked whether seven native annual forbs from the Great Basin Desert, USA, were capable of reducing biomass of the invasive annual grass Bromus tectorum, and if competition between forbs and B. tectorum could indirectly promote establishment of the native perennial grass Elymus multisetus. Some annual forbs were highly competitive with B. tectorum. For example, in a field experiment, Amsinckia tessellata reduced B. tectorum biomass by 97%, and Amsinckia intermedia, A. tessellata, and Descurainia pinnata reduced seed output between 79 and 87%. Adding native forbs to interacting B. tectorum and E. multisetus increased E. multisetus seedling growth rates in the greenhouse, but had no significant positive effects in the field. Strong suppressive effects of native forbs on B. tectorum might lead to indirect enhancement of perennial native species in subsequent years. While native colonizing species are often themselves considered “weedy”, they may be able to serve a transitory role in community recovery, allowing restoration in invaded systems to progress towards more desirable vegetation.