Plant diversity on Alberta rangelands is minimally affected by management intensive cattle grazing, study finds

The way ranchers graze their cattle doesn’t make much difference in plant diversity on the land, according to a U of A study.

That’s important because plant diversity is a useful metric to gauge the resilience of a landscape, including rangeland used by cattle producers, says Jessica Grenke, first author on the study.

Researchers compared adaptive multi-paddock grazing, called AMP, with other grazing systems more common in the northern Great Plains. AMP is a specialized rotational grazing practice that’s intended to emulate historical grazing patterns of large herds of animals moving rapidly across the landscape, leaving a long recovery period before being grazed again. 

AMP is more management intensive, employs higher inputs such as fencing and labour, and uses much higher densities of livestock relative to ranches that use regionally typical management. 

“Adaptive multi-paddock grazing has been studied and experimented with in more controlled settings for many years, and the scientific community has been left with contradictory results on what its impacts are ecologically,” says Grenke, a PhD candidate in the Department of Biological Sciences.

“In this study we’ve been able to see what’s actually happening on the ground.”

The findings suggest that AMP grazing is not an ideal solution to promote plant diversity.

Plant diversity is only one piece of the puzzle when it comes to rangeland (and ranch) management. Complementary studies by U of A researchers in this project have found ranches using AMP grazing practices lead to higher water infiltration and thus may help grasslands resist drought. Additional studies have focused on the diversity of soil microbes and the presence of carbon deposits in soil, all adding crucial context to the pros and cons of various grazing practices on various ecosystem goods and services.

AMP grazing has been around since the 1950s, according to Grenke. However, many studies looking at its ecological effects have had limitations, such as a lack of control ranches for comparison or concentration to a small locality not offering conclusive information. 

There are many practical and cost challenges to taking the broader approach this study used, says Grenke, who worked with Edward Bork, Cameron Carlyle, Mark Boyce and her supervisor, James Cahill on the project.