Debates over the effectiveness and benefits of a variety of grazing systems abound, and have been ongoing for well over a century. In 2008, Briske et al. (see Rotational Grazing on Rangelands: Reconciliation of Perception and Experimental Evidence) published a paper addressing this issue, concluding that there is no significant difference between “rotational” or “continuous” grazing systems in terms of outcomes for animal and plant productivity. Notwithstanding that these two categories of grazing system are extremely broad, and could mean innumerable things to different people, and that animal and plant productivity are certainly not the only important response variables to consider when managing grazing animals, this paper created quite a response in the range community, with some feeling validated, while others were upset and pointed to their land as evidence that this could not be true.
Briske et al. (2008) used a method called vote-counting, which could be considered a form of meta-analysis, albeit a relatively simplistic one that may not reveal the circumstances under which certain outcomes would result. I was in the room at a conference when the results of that paper were first presented, and the murmurings were loud. At the time, I remember thinking that the paper was well-presented, but I was curious about why they found what they found.
Five years later, in a course at U.C. Davis with Dr. Benjamin Z. Houlton, we were asked to conduct a meta-analysis on any subject of interest. I immediately thought of the Briske paper, and now, three years after that – and many frustrating setbacks later – my meta-analysis of the same dataset used by Briske et al. (2008) has been submitted to Rangeland Ecology & Management. This is a quantitative meta-analysis that investigates not only the outcomes of animal and plant productivity for the same set of studies chosen by Briske et al. (2008), but it also incorporates other influential factors, including climatic and managerial variables, revealing some interesting potential mechanisms behind the results.
I would also like to clarify that this paper (and Briske et al. 2008 paper) are NOT about holistic management, holistic planned grazing, or anything having to do with Allan Savory. While many of the original papers (~18) included by Briske et al. 2008 did cite Savory as an impetus for their experiments, the tested grazing methods were not akin to holistic planned grazing, and were not a test of holistic management. Most of the grazing experiments and methods bore little to no resemblance to holistic planned grazing, and most implemented a fixed, rigid grazing plan that did not allow for adaptation to plant growth, livestock weight gain, or other important factors that managers generally account for in their grazing planning (however they choose to go about it!). This paper is not about Allan Savory or holistic management; it is merely a re-analysis of a set of studies that compared many forms of “rotational” grazing to “continuous” grazing.
This paper was co-authored by Dr. Marc Horney from Cal Poly (CSU San Luis Obispo), whom I asked to come on board to ensure objectivity, thoroughness, and rigorousness. While I cannot yet share the full manuscript draft until it is actually published, I can share the abstract now, and if you are interested, you can check out the preliminary results that I presented a year ago at the 68th Annual Society for Range Management meeting (where I received first place in the PhD Oral Research Presentation category too, ego-booster…!) here: Continuous vs. rotational grazing, again: Another perspective from meta-analysis
This manuscript was submitted on 2/10/2016, resubmitted after the first round of revisions on 8/12/2016, and is now In Review. I will keep updating this site on the progress, but for now, here is title and revised abstract of the manuscript:
Title: Revisiting the rotational and continuous grazing system debate via meta-analysis
Abstract: In a recent meta-analysis of continuous- (CG) versus rotational-grazing (RG) systems, Briske et al. (2008) quantitatively reviewed 47 published journal articles comparing CG to different RG systems. They used vote counting to tally the number of studies that found significantly greater, equal, or lower production for CG relative to RG for three response variables: animal production (AP) per head (kg head-1) and hectare (kg ha-1) and plant production (PP, kg DM ha-1). They concluded that the two grazing systems produced similar results. We carried out a quantitative meta-analysis of the same dataset, moving beyond the vote-counting method to account for influential variables imbedded in the individual studies, such as local climate and management factors. We quantitatively evaluated the same studies in an attempt to harness the power of increased sample size with meta-analytical techniques. We examined sixteen predictors and selected interactions to determine their impacts on productivity outcomes and implications for management. Across all stocking rates AP was significantly higher for CG than RG, but PP was not. However, our analysis also found that multiple factors altered AP outcomes, including temperature seasonality, season of grazing, size of grazing area, number of replicates, number of paddocks in the RG system, within-experiment stocking rates, days in a RG grazing event, and precipitation. For example, total grazed areas (small- versus large-scale experiments) differentially affected outcomes of RG and CG: as scale increased, AP per ha increased under RG systems relative to CG systems. A better understanding how AP and PP are impacted by grazing system under the complexities of real-world conditions is necessary for assessing economic and ecological sustainability of grazing practices and guiding management. Quantitative meta-analysis is one tool that has potential for mining the growing body of experimental work for those details.
Keywords: animal production, Briske, livestock production, multi-paddock grazing, plant production, rangelands