The proliferation of unpalatable woody and grass weeds threatens the nation’s rangelands and their ability to produce wool, meat and various other services. Several management techniques have long been used to combat shrub and exotic grass encroachment, but are rarely sustainable from a livestock production standpoint because they have been reactive and focused on areas where encroachment has progressed to advanced stages. There has been little investment in development of proactive prevention strategies that are arguably more effective both ecologically and economically. This may be increasingly so under current and future climates.

We propose to focus on the critical shrub and exotic grass establishment phase and ask “How does herbivory by livestock, ants, rodent, and/or lagomorphs interact with precipitation to influence the probability of exotic grass and shrub seedling establishment in grassland?” This question will be addressed with large-scale experiments in Chihuahuan and Sonoran grasslands where precipitation will be manipulated to simulate dry and wet conditions. These treatments will be complemented by manipulations to assess the interactive effects of wild and domestic herbivores. Our results will fill knowledge gaps in integrated pest management and state and transition models. Information from the proposed study, coupled with a synthesis of literature on shrub encroachment and exotic plant invasion into grassland, will be used to develop an early-warning system to (a) alert managers to critical times and locations for inventory and monitoring for invasions, (b) identify windows of opportunity for early intervention, and (c) assist in prioritization of mitigation efforts. This early warning system “app” will be integrated into existing rangeland monitoring programs and an emerging crowd-sourcing framework.