Shrubs facilitate native forb re-establishment in an invaded arid shrubland

Establishing native species within invaded ecosystems is important to increase biodiversity and ecosystem functioning. Seeding species with nurse plants can be effective at increasing establishment especially in high stress ecosystems. Invaded arid ecosystems are thus good candidates for testing this method of seeding. It is hypothesized that shrubs will facilitate native forbs in an invaded arid shrubland through reductions in consumer pressure, abiotic stress, and competition from non-native species. Five native forb species were seeded in a full-factorial design into shrub and open microsites, with and without exclosures, and with and without non-native removals. The response of forbs was monitored in two growing seasons (2016, 2017). Shrubs had a positive or neutral effect on biomass, but had a neutral or negative effect on abundance in both years. Interestingly, most natives co-existed with non-natives species. Exclosures provided positive effects for biomass and abundance of some species and were important for species to establish. Seeding native forbs with shrubs improved the establishment of native species but grazing or herbivory may need to be minimized. The observed lack of native plant species in this region may not be from non-native species competition, but due to seed limitation and intense consumer pressure. •Shrubs increased the establishment of native forbs within an invaded arid system.•The facilitative effect was likely due to abiotic stress reduction not herbivore protection.•Herbivory was more limiting for natives than competition from invasive plants.