Alberta’s most abundant tree species under threat

The reasons aren’t known for certain but the widespread loss of poplars has significant implications for farming

Have you noticed that the poplar trees in your yard and in your bush are dying?

You’re not alone.

Alberta is experiencing a significant dieback of one of its most abundant species, and while some landowners are skeptical of the cause, evidence points to climate change as one possible contributor.

A massive poplar dieback is occurring throughout North America and this is only part of the problem. Where it is dying, it’s not growing back.

Whether the dieback is positive or a negative from a farming perspective depends on your point of view.

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Some landowners have chosen to convert land where dieback is occurring into pasture, said Toso Bozic, a provincial agroforestry specialist. But from an environmental, water retention, fire hazard and forestry perspective, it’s not good news, he added.

Trembling aspen, commonly called white poplar, is the most widely distributed wood species in North America and is a commercially important hardwood species that grows throughout Alberta. It is more abundant in the northern half of the province but there are about 3.4 million hectares of privately owned forests in Alberta that are pure or mixed-wood aspen stands. That’s about 70 per cent of the entire privately owned forest in the province.

Some landowners stand to lose a lot of money from this dieback as producers of oriented strand board (OSB) and pulp source between 10 and 20 per cent of their wood supply annually from private land in the province. That works out to between two million and three million tonnes of aspen.

Shelleen Gerbig has witnessed aspen dieback first hand, both as a farmer and a scientist with SARDA Ag Research, a non-profit organization directed by farmers in the municipal districts of Smoky River, Big Lakes, Greenview, and Northern Sunrise County.

This aerial view of a forest north of Grande Prairie taken in 2017 shows the massive scale of the poplar dieback.
photo: Canadian Forest Service

“Our farmyard has a lot of bush around it and is experiencing huge dieback of the aspen,” said Gerbig, who farms about 2,000 hectares near Falher.

The farm has one fully forested quarter section, and a number of poplars growing on fencelines and in their yard.

“Some of those trees are just old, but there is no regenerating growth, like nothing underneath to replace it. That’s also pretty much consistent with our fencelines.”

To compensate for the loss, they have planted mainly spruce as a replacement species.

Aspen dieback is widespread throughout the Peace Region, she said based on her observations while travelling for work.

“You notice it everywhere,” said Gerbig. “The trees just do not look healthy.”

However, aspen dieback isn’t necessarily being viewed as a negative by local landowners.

“Where we are farming, they are still in the (land) clearing mode,”she said. “So a dead tree is a good tree.”

But much of the land suffering aspen dieback is on marginal land, and having trees on that land is beneficial for neighbouring cropland.

“One thing that I think people should be concerned about is the loss of those natural areas where the natural pollinators and wildlife live,” she said.

What’s causing the dieback isn’t known, but climate change could be a factor, said Bozic.

“Based on the weather data I’ve reviewed, it would appear that climate change — resulting in more frost-free days and a drier climate — along with several other contributing factors is resulting in the aspen dieback issue in Alberta.”

He points to data assembled by University of Lethbridge researchers that shows the province’s weather is getting warmer, the growing season longer, the number of frost days declining, and the number of days of -10 C or lower only half of what it was in 1950. (The researchers used nearly five million Environment Canada daily temperature recordings from 6,833 locations across the province from 1950 and 2010 to create the Alberta Climate Records website:

In terms of dieback in the Peace Region, Gerbig isn’t convinced that warming temperatures are to blame. Chemical drift could be killing aspens along fencelines and there is significantly less forest being harvested for firewood, so there is less removal of older trees than in past years. Disease could also be an issue, she said.

Whatever the cause, dieback is not only occurring along fencelines and in yards, but in the middle of large woodlots and there is little regeneration taking place.

And it’s not just Peace Country being affected.

The Canadian Forest Service has been monitoring dieback in Alberta’s aspen forest since the mid-1990s, and also has 30 aspen research and monitoring sites across Western Canada, Ontario, and the Northwest Territories.

More than half the aspen tagged on these sites since 2000 are now dead, and the number of trees growing to replace them is in decline, said Mike Michaelian, a forest health technician and researcher with the forest service.

He points to two other factors that could partly explain the dieback.

“The northern half of Alberta has been exceptionally dry since 2000, with 2015 being one of the driest years in many parts of northern Alberta in probably more than 80 years,” he says. “We’ve also had a forest tent caterpillar infestation.”

This has increased the severity, speed, and extent of aspen dieback, he said.

As this dieback trend is expected to continue, Bozic suggests landowners survey their woodlots and put a plan in place to harvest wood before it loses its commercial value. This could include selling wood for production of bioenergy. The income could be used to implement a woodlot regeneration, although some landowners may choose to convert that land to agriculture production, he said.

On the positive side, aspen is a suckering species and new growth is more resilient. However, in some areas, particularly along the southern fringe of the aspen forest, there is no guarantee that an aspen stand will regenerate itself and may revert to a prairie landscape.

Landowners might want to plant coniferous species in the understorey, turning a pure aspen stand into a more resilient and valuable mixed-wood forest, said Bozic.

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