Dead or distressed birch trees are an increasingly common sight in yards throughout Alberta and the Canadian Forest Service wants to know why.
The federal agency has recently surveyed the condition of birches in about 50 Alberta communities, as well as communities in Saskatchewan, British Columbia and Washington state. The news isn’t good.
“What we found in a nutshell is that in the northern half of Alberta, decline of birch, which includes mortality and dieback, is generally fairly severe with the average percentage of trees dead or dying at about one third,” says David Langor, research scientist at the CFS Northern Alberta Forestry Centre.
But the survey also found the situation varies greatly from place to place.
For example, the rate of distressed or dying birch in northern Alberta communities is twice that of southern Alberta, where about 16 per cent of birches are in trouble. This was unexpected, since historically, southern Alberta receives significantly less moisture.
There is also huge variation within the northern part of the province. Lloydminster’s decline rate is only about seven per cent birch, compared to between 50 and 70 per cent in Edmonton. Researchers have also witnessed situations where one community is experiencing severe birch decline and a nearby one is experiencing no decline at all.
Langor says the prevailing theory is that birch decline is being caused by a combination of sustained drought, an insect called the bronze birch borer, and possibly a fungi associated with the insect. However, this is only a theory and it doesn’t explain the high rate of variability from one community to the next, or why birch in northern Alberta are in worse shape than in the south.
A new research program is being developed to solve this mystery. It will include creating a moisture pattern map and overlaying it onto a map of birch distress rates to gauge the impact of drought and investigating to see if the bronze birch borer has suddenly changed its behaviour to become more aggressive and if it’s carrying and spreading a destructive fungi.
“It could be that the insect is localized in certain areas and where it is present, you get this tree mortality increasing,” says Langor.
Another potential factor is the increasing number of warm spells during winter. Scientists want to know if this is possibly triggering a premature sap run in the birch.
A changing climate may be an underlying factor in all of these areas, says Langor.
“I often wonder if birch isn’t the canary in the coal mine because it is shallow rooted and perhaps more susceptible to drought,” says Langor. “Is it an early indicator of the impact of climate change? We don’t know. Interestingly enough, we’ve witnessed the same problem of dieback with balsam and sub-alpine fir over the past 20 years.”
Birch has limited commercial value in Alberta, save as firewood, but there has been recent interest in finding new uses for it. For example, there was a proposal by Ainsworth Lumber Company to build a hardwood sawmill using birch as the feedstock in the Valleyview area. As part of their follow-up research, CFS will expand its survey to see if naturally occurring birch in Alberta, Saskatchewan and B.C. forests are experiencing the same level of dieback as their urban cousins.
The CFS says there are a few remedial actions property owners can take to potentially save birch trees around their homes. They suggest heavy watering through drought periods and pruning dieback from the healthy tissue and disposing of it immediately.