Restoring native perennial grasses in medusahead habitat: Role of tilling, fire, herbicides, and seeding rate

Authors: SCHANTZ, MERILYNN - Red Rock Resources, Llc; Hardegree, Stuart; Sheley, Roger

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2018
Publication Date: 12/27/2018
Citation: Schantz, M., Hardegree, S., Sheley, R. 2018. Restoring native perennial grasses in medusahead habitat: Role of tilling, fire, herbicides, and seeding rate. Rangeland Ecology and Management. 72(2):249-259. https://doi.org/10.1016/j.rama.2018.10.012.
DOI: https://doi.org/10.1016/j.rama.2018.10.012

Interpretive Summary: Millions of hectares of rangeland in the western US are now dominated by invasive annual grasses that can dominate the landscape after wildfire. We tested the individual and combined impacts of prescribed fire, pre-emergent herbicides and seeding rate on both the control of annual grasses and initial seedling establishment of native and non-native grass species over a 4 year period. Although it was possible to effectively control annual grasses with prescribed fire and herbicide applications, the predominant driver of desirable seedling establishment was the sequence of favorable weather conditions during the fall, winter and spring. Ecologically based management treatments to address site availability, species availability and species performance have a positive impact on restoration outcomes, but favorable conditions of high spring precipitation, and low probability of post-germination freezing in the winter may be critical determinants of initial seedling success in most years. Land managers and restoration planners can enhance their probability of success with ecologically based management treatments, but need to adjust their expectations to the relatively low probabilities of having a positive sequence of weather events in any given year.

Technical Abstract: Invasive annual grasses continue to plague western U.S. rangelands, increasing their spread and dominance of these ecosystems annually. Ecologically based management strategies have emerged as useful tools to facilitate seeded species recovery in regions dominated by annual grasses. However, all seeded and resident species are unlikely to respond to management inputs similarly, especially among differing years with variable weather patterns. Quantifying how differing treatment years and ecologically based management inputs of prescribed fire, herbicide application, and seeding rates affect species colonization may provide valuable insights into plant community assembly following restoration. To quantify how differing years and management inputs affect seeded and existing resident plant species colonization, we assessed species biomass differences among two fire treatments, four herbicide rates, five seeding rates, and across four years in an eastern Idaho rangeland ecosystem. We found that treatment year was a key factor directing seeded species recruitment and seedling biomass was higher when winters had few freeze-thaw fluctuations and growing season precipitation was higher than normal. While burning combined with herbicide application produced lower annual grass and annual forb biomass, these treatments nor modifying seeding rate affected seeded species or resident forb biomass. Furthermore, while most species within a functional group responded similarly to management inputs, annual and perennial forbs had few similarities to management treatments, and species within both annual grass and perennial forb functional groups differentially