Scientists Look at Greenhouse Gas Emissions in Rangelands

Source: Saskatchewan Agriculture and Food

It seems nothing escapes the scrutiny of scientists when it comes to greenhouse gas emissions.

A team of researchers from the University of Saskatchewan recently completed an investigation of greenhouse gas emissions in Saskatchewan rangelands.

Global climate change has been linked in recent times to increases in atmospheric concentrations of greenhouses gases (GHG) due to the burning of fossil fuels, deforestation and changes in land use. The major GHGs of carbon dioxide, nitrous oxide and methane have always been produced naturally in the environment as a result of normal biological processes. But changes to the environment as a result of human activities can shift the balance of natural controls on these processes. It is the disruption of the natural controls on GHG production that has, in many case, led to an increase in production of these gases.

Estimates are that primary agriculture contributes approximately 10 per cent of Canada’s GHG emissions (source: AAFC). Rangelands, like other natural systems, will produce GHGs to some extent. Determining the magnitude of GHG emissions from rangeland will help Canada comply with its emission reduction targets, according to Yuguang Bai, project leader and associate professor with the Department of Plant Science at the University of Saskatchewan.

“GHG emissions from rangelands, especially those with hummocky terrain, are understudied—possibly due to complex interactions of landform elements, physical characteristics, disturbance and plant community, all of which vary in space and time," he explains. “The objectives of this study were to contrast the spatial variability of GHG emissions between protected and defoliated rangelands, to model landscape-level variations in GHG emissions and to correlate GHG [emissions] with landscape elements, biophysical factors, plant species diversity and forage production. In addition, we wanted to determine the relationship between range condition and soil carbon, as well as the effect of shrub invasion on soil carbon. Finally, we hoped to provide baseline data for optimal pasture management to maximize economic and ecological returns.”

To achieve this, Bai and his colleagues conducted three experiments in central and southern Saskatchewan between 2003 and 2005. The areas studied covered the mixed grassland and moist mixed grassland ecoregions.

A number of landform elements were looked at for the GHG experiment, such as the north-facing concave aspect, the north facing convex aspect, the south facing concave aspect, level upland and depression, within hummocky landscapes.

“We applied a defoliation treatment in April to simulate grazing, among other things, and we measured carbon dioxide and other gas emissions every seven to 10 days, from spring until fall, with chambers designed specifically for this purpose," says Bai. “We found that particular landscape elements significantly affected the flux of carbon dioxide and nitrous oxide. We also found that biophysical characteristics, such as soil temperature and water content, as well as plant species composition, also varied among landscape elements, contributing to variations in GHG fluxes. The greatest GHG flux was found in the depression. Mowing increased the positive flux of carbon dioxide and nitrous oxide while increasing the negative flux of methane.”

The scientists also selected nine sites on which to study the effect of shrub invasion on soil carbon. Results showed that, along a gradient from grassland to shrub communities, soil organic carbon (SOC) had a less than five per cent increase. Effectively, there was no significant difference in SOC between the different plant communities.

Another nine sites were selected to study the effect of cattle grazing on soil carbon. Investigation revealed that grazing did not significantly affect SOC. The researchers found that soil carbon was controlled more by soil texture than by shrub cover or grazing, with loamy soils having greater SOC and root biomass than sandy soils.

“Overall, the mixed prairie of Saskatchewan likely contributes very little to GHG emissions,” concludes Bai. “Properly managed, the mixed grass prairie has a well-balanced nutrient cycle that includes various GHGs. The grassland ecosystem plays a role in mitigating climate change by retaining carbon that would otherwise be released into the atmosphere if poor grazing management or conversion to arable agriculture occurred.”

It appears current management practices aiming at sustainability and fostering the integrity of grassland ecosystems should be maintained.

Support for this study was provided by the Agriculture Development Fund of Saskatchewan Agriculture and Food, the BGSS program of the Canadian Agri-Food Research Council and the University of Saskatchewan. The other investigators were doctors Brian McConkey, Dan Pennock, Jim Romeo and Rich Farrell, former Masters student Matthew Braun and Ph.D. candidate Tyler Colberg.

The final report of this study can be downloaded as a PDF document at:

http://www.agr.gov.sk.ca/apps/adf/adf_admin/reports/20020082.pdf

For more information, contact:

Yuguang Bai, Associate Professor
Department of Plant Sciences
University of Saskatchewan
(306) 966-4955

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