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.

Products & Media 

Rutherford WA, SR Archer¬, L. Weber-Grullon, OE Sala. (2021) Shrub (Prosopis velutina) recruitment in Sonoran grasslands: precipitation, not herbaceous cover, matters most. Poster presentation; 74th Annual Society for Range Management Meeting, Virtual Meeting.

Rutherford WA, SR Archer¬, L. Weber-Grullon, OE Sala. (2020) Monsoon season precipitation variation, not herbaceous cover, controls shrub (Prosopis velutina) recruitment in Sonoran grasslands. Poster presentation; Ecological Society of America Annual Meeting, Virtual Meeting.

Rutherford WA, SR Archer¬, L. Weber-Grullon, OE Sala. (2020) Velvet mesquite recruitment in Sonoran grasslands: grass utilization is of little consequence to Monsoon season precipitation variation. Oral presentation; AZ Section-Society for Range Management Winter Meeting, Wickenburg, AZ.
Rutherford WA and SR Archer. Evaluating Shrub Encroachment Risk on Sonoran Desert Rangelands. Poster presented at SER-SW Chapter Annual Meeting, Tucson, AZ.

Rutherford WA, SR Archer, L Weber-Grullon, OE Sala. "Shrub recruitment in Sonoran Desert grassland: grass utilization is of little consequence to intra-seasonal precipitation variation." Poster presented at the Society for Range Management Annual Meeting 2019, Minneapolis, MN LINK

Rutherford WA, SR Archer, JWD van Leeuwen. "A Decision Support Tool for Predicting Risk of Woody Plant Encroachment on Rangelands." Poster presented at 15th Annual RISE Symposium 2018, Tucson, Arizona. LINK

Rutherford WA, SR Archer, L Weber-Grullon, OE Sala. "Shrub (Prosopis velutina) recruitment in a semi-arid grassland: precipitation-herbivory interactions reveal few constraints." Poster presented at Ecological Society of America Annual Meeting 2018, New Orleans, Louisiana. LINK

Rutherford WA, KA Mathis, L Weber-Grullon, OE Sala, SR Archer. "Does seed predation limit velvet mesquite (Prosopis velutina) recruitment in grasslands?" Poster presented at RISE 2017. LINK


Rain-out shelters at the Santa Rita Experimental Range.

Automated Rainfall Manipulation System (ARMS).

Velvet mesquite (Prosopis velutina) seedlings.

Velvet mesquite (Prosopis velutina) seedlings that have experienced recent herbivory.