Novel Approaches to Invasive Annual Grass Management: Assessing Efficacy and Impacts on Target Species and Plant Diversity

Abstract

Aims. The management of invasive species is a global concern that requires a paradigm shift away from only assessing control efficacy to also including impacts to the diversity of the surrounding plant community. Many rangelands in the western United States are invaded by annual grasses like Bromus tectorum (cheatgrass). Current management of invasive annual grasses (IAGs) relies heavily on herbicides and their efficacy in targeting IAGs. However, this approach often does not consider the response of the surrounding plant community. Evaluations of alternative management options and the efficacy of all approaches on target and desired vegetation are needed. We assessed four management options and a restoration seeding split treatment to control B. tectorum and restore the desired plant community. Location. Semi‐arid grasslands, southwestern Montana, United States. Methods. We monitored vegetation for three growing seasons after management treatment application (non‐treated control, mustard seed meal (MSM), NutraFix, and indaziflam) and restoration seeding (native grasses) with spatial (3) and temporal (2) replication, assessing changes in B. tectorum cover, species richness, alpha and beta diversity, and rank abundance. Results. The MSM provided control for 1 year but also reduced species richness, and B. tectorum was highly dominant 2 and 3 years after treatment. NutraFix provided control for 2 years and had no meaningful impacts on species richness or alpha diversity. Indaziflam provided 3 years of B. tectorum control, reduced species richness, and facilitated a shift toward a Pascopyrum smithii (western wheatgrass) dominated community. Restoration seeding did not affect B. tectorum cover nor beta diversity but did increase richness and alpha diversity. Conclusions. This study demonstrates the importance of a paradigm shift away from evaluating only management efficacy of the target species to include other species and metrics that support recovery of the desired plant community.