April 15, 2019

Climate change to impact grizzly bears in the Rocky Mountains by century's end

UCalgary geographers predict a shortage of bears' food source in the months before hibernation

Local climate projections by the University of Calgary’s Department of Geography show that in as little as 60 years from now buffalo berries in the Rocky Mountains will ripen three weeks earlier than they do currently, a shift which will have major implications for grizzly bears in the area, who rely on the berries as one of their most important food resources.

This three-week advance in the buffalo berries’ peak fruiting will widen the gap between the availability of the grizzlies’ “seasonal berry buffet” and the time in which the bears hibernate, says Dr. Greg McDermid, PhD, a geography professor and researcher on the study, newly published in the scientific journal Nature Climate Change. 

“This development will change the behaviour of the grizzly bears, who are very food focused,” McDermid explains. “We can expect to see them at times and in places where we’re not used to seeing them. I think it could be argued that we’re already witnessing that.”

This revelation about the predicted early fruiting of the buffalo berries and its impact on grizzly bears came as part of a breakthrough in tracking the phenology of plants beneath the forest canopy, using a framework developed by Dr. David Laskin, McDermid’s former PhD student and lead author of the study.

Phenology is the timing of seasonal activities in plants and animals, such as the stage in which a plant moves from flowering to fruiting. Laskin explains that this is a powerful lens through which to observe climate change, as ecological communities are affected profoundly by climate. 

Today, satellites routinely track major phenological events, such as spring green-up, across the globe. “The problem is, these satellites can’t see what’s going on in the understory, beneath the forest canopy,” says Laskin. “And that’s where many ecosystem processes are taking place.” 

Laskin developed a novel and remarkably accurate way of tracking the phenology of plants in the understory by using satellite-derived measures of temperature accumulation. 

“There is a horticultural principle which says that plant development is tied very tightly to temperature accumulation,” explains Laskin. “A plant needs a certain amount of heat to proceed from one phenological stage to the next. It is this sensitivity to temperature that makes plants act as such good bioindicators of climate change. This is what our framework monitors, the rate at which plants are developing in the understory, across huge areas.” 

With the buffalo berries ripening three weeks earlier, as per the forecasted impacts of climate warming, the duration of the berries’ availability will also be abbreviated, notes Laskin. “This means that the grizzlies will have less time to forage for their most important caloric food source before hibernation. This might lead them into places where they wouldn’t normally go. Places where they might get themselves into trouble.” 

McDermid adds that this research could also help land managers monitor seasonably available grizzly bear foods in “near-real time.”

“If you’re a land manager and you’re trying to decide whether or not to close a campground or restrict industrial activity because there’s going to be bears attracted to that area, then this is a great predictor of that.” 

The research also aims to help ecologists understand how climate change may impact forest ecosystem dynamics, both in Alberta and beyond.

Bear Infographic