Adaptive rotational grazing and the story of the regrazed grass plant

Authors: Porensky, Lauren; Wilmer, Hailey; Augustine, David; Derner, Justin; FERNANDEZ-GIMENEZ, MARIA - Colorado State University; BRISKE, DAVID - Texas A&M University

Submitted to: International Grasslands Congress
Publication Type: Abstract Only
Publication Acceptance Date: 3/4/2020
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Livestock stocking rates and decisions about how to move animals in time and space can both impact plant responses to livestock grazing. We report on a ranch-scale collaborative experiment comparing adaptive rotational grazing management to season-long continuous grazing during a 4.5-month summertime growing season. As part of this project, stakeholders and scientists worked to articulate their hypotheses about the mechanisms linking rotational grazing with expected vegetation outcomes. Several stakeholders expected rotational grazing to enhance the production and diversity of more grazing-sensitive grass species. The main hypothesized mechanism underlying this expectation was that rotation should reduce regrazing of these grass plants. To test this hypothesis, we monitored levels of grazing and regrazing on individual tillers (ramets) of a grazing-sensitive grass species, Pascopyrum smithii, for three consecutive years. We measured regrazing rates in pastures managed using moderate stocking and adaptive rotational grazing as well as pastures grazed continuously, season-long at light, moderate, or heavy stocking rates. Tillers in heavily grazed pastures were regrazed more than 3 times as frequently as tillers in moderately grazed pastures, reinforcing the importance of stocking rate as a driver of vegetation impact. At the ranch-scale, tillers were regrazed equally often under adaptive rotational and season-long continuous grazing management, and this result did not vary across years. Adaptive rotational grazing greatly increased heterogeneity among pastures in levels of regrazing, with some pastures experiencing heavy grazing and others experiencing light grazing. In this semi-arid rangeland, tiller defoliation data do not support the hypothesis that adaptive rotational grazing leads to less regrazing at the ranch-scale. In line with these mechanistic results, the production and diversity of grazing-sensitive grasses also failed to respond to adaptive rotational grazing after 5 years. However, adaptive rotational grazing may enhance management flexibility and provide opportunities to work towards other objectives, such as wildlife habitat.