Collaborative adaptive rangeland management, multi-paddock rotational grazing, and the story of the regrazed grass plant

Authors: Porensky, Lauren; Augustine, David; Derner, Justin; WILMER, HAILEY - Us Forest Service (FS); LIPKE, MEGAN - University Of Wisconsin; FERNANDEZ-GIMENEZ, MARIA - Colorado State University; BRISKE, DAVID - Texas A&M University

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/27/2021
Publication Date: 9/1/2021
Citation: Porensky, L.M., Augustine, D.J., Derner, J.D., Wilmer, H., Lipke, M., Fernandez-Gimenez, M., Briske, D. 2021. Collaborative adaptive rangeland management, multi-paddock rotational grazing, and the story of the regrazed grass plant. Rangeland Ecology and Management. 78:127-141. https://doi.org/10.1016/j.rama.2021.06.008.
DOI: https://doi.org/10.1016/j.rama.2021.06.008

Interpretive Summary: Two limitations of past studies on rotational grazing are their limited spatial extent (small paddocks) and the use of fixed grazing schedules that ignored human dimensions of adaptive decision-making associated with multi-paddock rotational grazing. To address these limitations, we investigated tiller defoliation dynamics of western wheatgrass within the Collaborative Adaptive Rangeland Management (CARM) experiment, located in the shortgrass steppe of eastern Colorado. Our study was inspired and guided by the hypotheses and mental models of the CARM stakeholder group. Designing the study within an existing collaborative process allowed us to examine applied ecological questions at a manager-relevant spatial scale in a rigorous way, and then feed our findings back into the group’s decision-making process. We found that collaborative adaptive multi-paddock rotational grazing did not lower rates of grazing and regrazing on western wheatgrass tillers at the ranch-scale in the shortgrass steppe, when compared to season-long continuous grazing at the same stocking rate. Thus, the use of adaptive multi-paddock rotational grazing should not be expected to enhance the production or abundance of this palatable, cool-season species. Moreover, our results show that at the scale of individual grass plants, season-long rest is built into season-long continuous grazing as well as rotational systems. Although grazing system did not impact tiller defoliation patterns at the whole-ranch scale, we found higher and predictable variability in defoliation frequency among pastures within the rotational treatment. Managers could use this variation to strategically minimize or maximize the impacts of grazing on western wheatgrass at the individual pasture scale. The collaborative adaptive management model enabled our team to directly address key stakeholder hypotheses, and enhanced stakeholder ownership and trust of research results.

Technical Abstract: Frequent, severe defoliation reduces grass production, particularly for grazing-sensitive species. Multi-paddock rotational grazing has long been proposed as a grazing strategy that may be able to reduce the frequency and intensity of defoliation on palatable grass plants without altering stocking rates. Previous studies evaluated this hypothesis using small, homogeneous paddocks and non-adaptive rotation schedules, and found small and inconsistent differences between continuous and rotational grazing systems. Using a stakeholder-driven Collaborative Adaptive Management (CAM) framework, we conducted the first ranch-scale experimental investigation into tiller defoliation dynamics in the context of adaptive multi-paddock rotational grazing. We monitored tiller defoliation frequency and intensity in ten paired 130-ha pastures which were assigned to either a collaborative adaptive multi-paddock rotational grazing treatment (CARM, one livestock herd) or a season-long continuous grazing treatment (TRM; ten separate livestock herds) in shortgrass steppe. Consistent with previous studies, we observed that frequencies of grazing and regrazing on a palatable, cool-season grass (western wheatgrass, Pascopyrum smithii) were much more sensitive to stocking rate than grazing system treatment. Under the moderate stocking rates used in both CARM and TRM treatments, roughly two-thirds of western wheatgrass tillers remained ungrazed annually, regardless of grazing system. Thus, season-long rest is present in season-long continuous grazing as well as rotational systems. Levels of regrazing in CARM and TRM were low (5-15%) and similar between treatments. Although defoliation dynamics were similar between CARM and TRM at the whole ranch scale, CARM enhanced spatial and temporal heterogeneity in defoliation frequencies among individual pastures. Managers implementing adaptive, multi-paddock rotational grazing could use this heightened and predictable variability to strategically minimize or maximize impacts of grazing on western wheatgrass at the individual pasture scale. The CAM model enabled our team to identify and directly address key stakeholder hypotheses, and resulted in co-production of management-relevant research.