A patch of grassland in Alberta that hasn’t been grazed for 30 years has less carbon and diversity than grazed prairie
LUNDBRECK, Alta. — A fragment of the 65,000-acre Waldron Grazing Co-operative has been fenced off for 30 years in an “exclosure” protected from grazing animals and man-made disturbance.
Compared to the grassland just outside the wire, it has fewer plant species and long, weathered grass.
Waldron manager Mike Roberts bent down to search through the thick thatch, easily extracting handfuls of wiry rough fescue to show those on a grazing event organized by the Foothills Forage and Grazing Association.
“It’s beautiful isn’t it? Beautiful rangeland. A couple problems. One, it’s not natural. Two, there’s no economic benefit. By not natural, I mean there’s no grazing, there’s no fire, so this is actually a man-made situation.”
In contrast, the grassland grazed in a managed process by about 13,000 head of cattle has multiple species, less thatch and younger, more tender grass. For Roberts, it’s an indication that grazing benefits the grassland, the ecosystem and the ranchers who run cattle there.
“From a rancher’s perspective, this is not a natural situation,” Roberts said about the exclosure.
“It has no economic benefit to us as ranchers because we have to have economic benefit to own the land. If we don’t own the land, what’s it going to be? Is it going to be small acreages overgrazed by the four fat horses that live on it? We’ve all seen it a thousand times.… We have to have economic benefit out of our land, so that means we have to graze it.”
University of Alberta range ecologist Ed Bork said the Waldron exclosure is one of 114 across the Prairies that he is studying. He has examined vegetation, biomass above and below ground, root mass, leaf litter and soil carbon.
Mike Roberts, manager of the Waldron Grazing Co-operative in southwestern Alberta, says research on the ranch shows grazing is an important part of healthy perennial grassland. | Barb Glen photo
In April, he published a paper on some of the findings, entitled Quantifying Carbon Stocks across Alberta’s Grasslands in Support of a Provincial Carbon Strategy.
The carbon storage capacity of grazing land versus that in the exclosure was among the findings.
“We actually had higher soil organic carbon concentrations outside the exclosures and not inside the exclosures where livestock grazing had been removed for anywhere from 20 to 60 years,” said Bork.
Prairie grasslands evolved under grazing, initially from bison and then from cattle and wildlife. Bork said he found higher root biomass in grazed areas, as well as plant diversity including broadleafed species, low- and medium-stature forbs, and a variety of grass species.
“If you don’t have that diversity of vegetation, you don’t have that highly favourable root mass accumulation where plants are constantly trying to renew themselves.”
Grasslands sequester carbon but they also have a net consumption of methane and nitrous oxide, two greenhouse gases considered to be culprits in climate change.
Bork noted that cows are often criticized for belching methane.
“But the other half of the story that is being neglected is that healthy grasslands also are a sink for methane. There are microbes that actually break down and scrub methane from the atmosphere,” he said.
Thus a full accounting of greenhouse gases must involve how much is produced as well as how much is taken up by grasslands.
“That’s the only fair way to assess the value of these ecosystems, including under grazing.”
Bork and his colleagues are also studying adaptive multi-paddock grazing to see if land under that system is more efficient at building carbon. Twenty-six ranches are involved in the three prairie provinces.
They have also compared the respective greenhouse gas footprints of cropland with shelterbelts, cropland with natural hedgerows and pasture with aspen. The latter category, pasture with aspen, had the lowest footprint, which he contended was because of the pasture.
“The nice thing about grasslands is, if you get a fire over this, the vast majority of the carbon is still protected. If the forests burn, the carbon is exposed and it goes back up to the atmosphere.”