Sustainable Livestock Production on the Frontier: Plant and Soil Responses to Simulated Managed Grazing in Sub-Arctic Alaska

Sustainable Livestock Production on the Frontier: Plant and Soil Responses to Simulated Managed Grazing in Sub-Arctic Alaska

Summary

Healthy, productive pasture ecosystems are the key to providing high quality forage for raising livestock and minimizing dependence on purchased feed. Grazing is the main biotic disturbance regime on pasture ecosystems. The frequency and intensity of the disturbance is measured by the number of animals grazed per unit of land (or stocking rate) and length of time that the animals are left to remove forage. The carrying capacity of the land is determined by the response of the pasture ecosystem to the stocking rate and length of grazing period. Indicators such as plant production, percentage of bare ground, and soil surface quality are used to visually assess the changing effects. The pasture ecosystem responds to the three main mechanisms of grazing disturbance: herbivory, dung and urine deposition, and trampling. The carrying capacity of the land is a key component to the economic viability of an agricultural livestock operation, as acreage is one of the main limiting factors to herd size and economies of scale. Intensively managed rotational grazing (IMRG) is advocated by many ranchers, and some in the scientific community, as a grazing management technique that simultaneously increases stocking rates and enhances the pasture ecosystem health [1-3]. Understanding the region specific role of these mechanisms in the context of intensive short duration rotational grazing is critical to assessing and predicting the potential impact of a change in grazing management. 

Managing a robust pasture ecosystem and optimizing available forage in the sub-arctic interior of Alaska is a challenge. The region is characterized by a short growing season, slow decomposition rates, and undeveloped soils that are sensitive to compaction and erosion. Although grazing practices in Alaska are frequently characterized as continuous, they are largely unmanaged. Here, as elsewhere, unmanaged grazing results in a heterogeneous pattern of pasture use with animal feeding preferences creating patches of both over- and under-utilization, and degradation. The goal of this research is to evaluate the response of pastures to IMRG and increase our understanding of the roles that grazing mechanisms have in the sub-arctic pasture ecology.

To evaluate the impacts, a full factorial experiment of simulated trampling, manure/urine deposition, and forage removal is being conducted, mimicking the intensity and frequency of an IMRG. The simulations are being conducted on plots in two established pastures with different soil types over the 2014 and 2015 grazing seasons at the Robert G. White Large Animal Research Station (LARS). The treatments were applied to 48-1 m² plots in the two pastures over the 2014 grazing seasons. In addition to continued application of the treatments to the 2014 plots, another 48 plots were established adjacent to the initial plots in 2015. These plots will allow us to compare one versus two years of IMRG treatment and control for variation between years. Changes in soil biota, physical soil characteristics, plant biomass, and plant community composition are being measured. Preliminary results of plant biomass have shown that the treatments have had a marked impact on biomass productivity (p<0.001). In addition to increased biomass, we anticipate increased microbial activity, improved soil organic matter, and beneficial plant species composition in plots that received all three grazing mechanisms. We will evaluate the relative role of each grazing mechanism to determine if trampling has an elevated role in nutrient cycling, as has been shown in Swedish sub-arctic pastures [3, 4].  This research provides a twofold benefit; it evaluates site-specific responses to IMRG and provides insight on the relative roles of grazing disturbance mechanisms on sub-arctic soil and plant health.

1. 1. Teague, W.R., et al., Grazing management impacts on vegetation, soil biota and soil chemical, physical and hydrological properties in tall grass prairie [electronic resource]. Agriculture, ecosystems & environment, 2011. 141(3-4): p. 310-322.

1. 1. Jacobo, E.J., A.M. Rodriguez, N. Bartoloni, V.A. Deregibus, Rotational grazing effects on rangeland vegetation at a farm scale. Rangeland Ecology & Management, 2006. 59: p. 249-257.

1. 1. Olofsson, J., et al., Effects of summer grazing by reindeer on composition of vegetation, productivity and nitrogen cycling. Ecography, 2001. 24(1): p. 13-24.

1. 1. Sorensen, L.H., J. Mikola, M. Kytoviita, and J. Olofsson, Trampling and spatial heterogeneity explain decomposer abundances in a sub-arctic grassland subjected to simulated reindeer grazing. Ecosystems, 2009. 12(5): p. 830-842.

• Simulating trampling using weighted tractor tire – Photo by Edwin Remsberg
• Simulating herbivory treatment – Photo by Edwin Remsberg

Objectives/Performance Targets

The goal of this study is to evaluate the effects and interaction of simulated herbivory, manure/urine deposition, and trampling in response to IMRG methodology.  The research will provide regionally specific baseline information and address some crucial knowledge gaps through the following objectives:

1. 1. Determine how an intense but brief simulated grazing disturbance affects the physical structure of pasture soils and plant communities.

1. 1. Measure changes in abundance and community structure of soil organisms and consequent effect on decomposition.

1. 1. Evaluate the relative and interactive roles of the three grazing mechanisms: herbivory, manure/urine deposition, and trampling in sub-arctic pastures.

These objectives are being met by the completion of the 2014 phase of the experiment and the progress of the 2015 phase. Targets have been met at every stage of implementation. Baseline soil samples have been analyzed by Ward Laboratories using phospholipid fatty acid (PLFA) assays to detect changes in the soil microbial community and Haney tests to assess soil health and nutrient availability. Soil samples from May 2015 are ready for analysis. Ongoing biomass data is being collected and some plant species composition changes have been observed. A soil penetrometer was purchased to measure changes in penetration resistance. The treatment, data collection, and analysis have not deviated from the proposal materials and methods. Treatments are scheduled to continue in response to forage growth. Soil samples, penetration resistance, and plant species composition will be measured at the end of the 2015 grazing season. A comprehensive statistical analysis will be performed at the conclusion of the study in September 2015.

Accomplishments/Milestones

We successfully completed the first year of the experiment. The end of our second year is rapidly approaching. We felt that the initial results warranted the replication of the study in the 2015 grazing season. As a result we were able to establish 48 new plots this spring in addition to the continued treatment of the 2014 plots. This expansion of the experiment has allowed us to replicate the study temporally, complementing the spatial replication. In addition to the milestones associated with the implementation of the experiment, I participated in six education/outreach events. I had the opportunity to speak at both the 2014 and 2015 Alaska Sustainable Agriculture Conferences that were funded by the Western Sustainable Agriculture Research and Education Program (SARE) and a field day organized by the Fairbanks Soil and Water Conservation District. The sustainable agriculture conferences had 180-220 attendees. The research was also presented in two college classes and one high school class.

Impacts and Contributions/Outcomes

At the 2014 Western SARE funded Alaska Sustainable Agriculture Conference, I introduced the concept of Holistic grazing and the research to local stakeholders. I sought their input and suggestions during the meeting. I spoke at the 2015 Alaska Sustainable Agriculture Conference about the economic sustainability of grazing livestock and efficient pasture resource usage using muskoxen as an indigenous livestock species. The annual Alaska Sustainable Agriculture Conference is well attended by local producers in the state and proved to be an excellent venue to solicit feedback and convey the status of the ongoing research. In August 2015, at a field day with the Fairbanks Soil and Water Conservation District, I had the opportunity to show my research to producers that visited LARS.

At the University of Alaska, Fairbanks, I taught a class in Soil Biology (400 level) and another in Principles of Sustainable Agriculture (200 level) where I presented my research to undergraduate students and discussed the context of the experiment within the subject matter of the class. The summer of 2015, I presented my research to a science summer camp, Methods in Molecular Biology, for high school students at the Ilisagvik College in the Barrow, AK (the northernmost city in the U.S.).

In the upcoming year, I am scheduled to present the results of the research at the 2016 Society for Range Management Annual Meeting in Corpus Christi, TX, and the 2016 Alaska Sustainable Agriculture Conference in Anchorage, AK.  The education and outreach efforts are targeted at providing community stakeholders with information on grazing and associated impacts specifically for interior of Alaska. It is my goal to improve the understanding of the impacts associated with managed grazing on the sub-arctic plants and soil to help producers make informed decisions on grazing management strategies that reduce costly imported inputs, improve economic returns, and promote agriculture in Alaska.

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