Combining active restoration and targeted grazing to establish native plants and reduce fuel loads in invaded ecosystems

Authors: Porensky, Lauren; PERRYMAN, BARRY - University Of Nevada School Of Medicine; MADSEN, MATTHEW - Brigham Young University; WILLIAMSON, MATTHEW - University Of California; LEGER, ELIZABETH - University Of Nevada School Of Medicine

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/2018
Publication Date: 1/2/2019
Citation: Porensky, L.M., Perryman, B.L., Madsen, M., Williamson, M.A., Leger, E.A. 2019. Combining active restoration and targeted grazing to establish native plants and reduce fuel loads in invaded ecosystems. Ecology and Evolution. 8:12533-12546. https://doi.org/10.1002/ece3.4642.
DOI: https://doi.org/10.1002/ece3.4642

Interpretive Summary: In the western United States, many sagebrush steppe plant communities have been converted to invasive-dominated, fire-prone annual grass communities. Livestock can be used to reduce invasive plants and associated fire risk in invaded sagebrush steppe sites. However, we know little about impacts of targeted grazing on native plants or restoration in this system. We determined how targeted grazing interacted with multiple restoration treatments to affect standing biomass and seedling densities of planted grasses. Across all planting treatments, ungrazed paddocks had the highest second-year seedling densities, but also the highest wildfire risk. Paddocks grazed in fall of the second growing season had fewer seedlings than paddocks grazed in spring, five months later. Several restoration treatments, including high seed rates and seed coating technologies, minimized the negative effects of grazing on seedling establishment. Planted species had variable responses to treatments. For example, Elymus trachycaulus (slender wheatgrass) and Poa secunda (Sandberg’s bluegrass) had the highest second-year seedling densities, but achieved this via different pathways. Elymus trachycaulus produced the most seedlings in year one, but was very sensitive to grazing, whereas Poa secunda had moderate first-year establishment but high survival, even when grazed. We identified clear tradeoffs between mitigating wildfire risk and establishing native grasses in invaded sagebrush steppe. However, tradeoffs were minimized by restoration strategies including high seed rates, species selection, seed coating, and targeted timing of grazing. In systems threatened by non-native plant species, targeted grazing by non-native herbivores may create opportunities for managers to achieve multiple objectives, such as reducing wildfire risk while simultaneously establishing desired native plants.

Technical Abstract: The simultaneous introduction of non-native herbivores and non-native plants can dramatically change ecosystem dynamics as well as management options and outcomes. In the western United States, sagebrush steppe plant communities have been converted to invasive-dominated, fire-prone annual grass communities, and grazing with domesticated livestock is now common. Livestock can be used to reduce the abundance of invasive plants and associated flammable fuels in invaded sagebrush steppe sites. However, we know little about impacts of targeted grazing on native seedling establishment in this system. We used a broad-scale, manipulative experiment to determine how fall or spring grazing treatments interacted with seed rate, planting arrangement, seed coating technology, and species identity to affect standing biomass and densities of seeded species. Across all planting treatments, ungrazed paddocks had the highest second-year seedling densities, but also the highest standing biomass, and therefore fuel loadings. Paddocks grazed in fall of the second growing season had fewer seedlings than paddocks grazed in spring, five months later. Several restoration treatments, including high seed rates and seed coating technologies, minimized the negative effects of grazing on seedling establishment. Planted species had variable responses to treatments. For example, Elymus trachycaulus and Poa secunda had the highest second-year seedling densities, but achieved this via different pathways. Elymus trachycaulus produced the most seedlings in year one, but declined in response to grazing, whereas P. secunda had moderate first-year establishment but high survival across grazing treatments. We identified clear tradeoffs between mitigating wildfire risk and establishing native seedlings in invaded sagebrush steppe. However, tradeoffs were minimized by restoration strategies including high seed rates, species selection, seed coating, and targeted timing of grazing. In systems threatened by non-native plant species, targeted grazing by non-native herbivores may create opportunities for managers to achieve multiple objectives, such as reducing wildfire risk while simultaneously establishing desired native plants.