Effects of Vertebrate and Invertebrate Herbivory on Seedling Establishment and Survival in Seeded Rangelands in Western Utah, USA

ABSTRACT Successful rangeland revegetation on western rangelands can be challenging with natural and human-related influences. Defoliation from a wide range of vertebrate and invertebrate grazers can reduce seedling growth and increase plant mortality, thereby impeding restoration efforts. Understanding how herbivory can impede plant establishment and growth may help predict restoration outcomes and create effective solutions for rangeland restoration. Bottlebrush squirreltail ( Elymus elymoides (Raf.) Swezey), a native perennial grass species often used in seed mixes, stabilizes soils, provides quality forage, and competes with annual plants. The purpose of this study was to identify the impact of herbivory on bottlebrush squirreltail seedling damage and mortality. This study was conducted on the Utah Test and Training Range (UTTR) in western Utah, USA, tracking herbivory, seedling emergence, and timing and cause of seedling death. We placed cameras in 28 randomly placed plots arranged in a randomized split-plot design with fenced and unfenced plots and seeded with two rows of bottlebrush squirreltail. We tracked individual seedlings and recorded their condition (alive, dead, grazed or damaged), comparing establishment and survival between fenced and unfenced plots. Seed predators reduced initial seedling establishment in unfenced plots by four times ( P = 0.0002). Seedlings were seven times more likely to survive in fenced vs. unfenced plots. Of total seedling mortality, 73.6% of seedling death was caused by herbivory from black-tailed jackrabbit ( Lepus californicus ), invertebrate herbivores, and Botta’s pocket gopher ( Thomomys bottae ). Strategies to mitigate the effect of herbivores should be considered to increase seeded plant establishment during restoration efforts. These results highlight the broader need for restoration projects in arid and semi-arid ecosystems to account for herbivore communities when planning seeding projects, as early-stage herbivory can strongly limit plant establishment across many species and ecosystems.