Climate Change and the Eastern Ontario Woodlot

February 9, 2008

Before he retired Bob Stewart was the Climate Change Research Coordinator for the Canadian Forest Service. Here are my notes from his lecture at the Eastern Ontario Model Forest Owners annual meeting in Watson’s Corners on February 9th.

“One in sixteen jobs in Ontario is related to forest products, so the impact of climate change is something we must anticipate and manage, though we have the tools and the time to do so.”

For the period 1941 to 1970 the growing season averaged 145 days (May 13 to Oct. 5). From 1971 to 2000 it averaged 160 days (May 2 to Oct. 9). From 2040 to 2060 the model projects a growing season of 175 days (April 24 to Oct. 16).

Extreme weather events are becoming more common. With a projected average 2 degree C. increase in temperature, the 1 in 100 chance of an extreme weather event like a major ice storm becomes more like a 1 in 25 chance.

While other areas of North America will face major upheavals, Eastern Ontario will only be a little warmer over the next fifty years, though precipitation levels will also increase slightly. That is not to say trees won’t face stress, however, because the precipitation/evaporation index doesn’t look good. According to the model, in the hot part of the summer only 75% of the moisture lost to evaporation will come back as precipitation.

Stewart showed a map of the current and projected ranges of the hemlock tree. There’s a wide band between the shaded areas, so it’s obvious that the seeds won’t readily make the 200 mile trip to the southern part of the new zone on their own. “We will see very significant species mix changes in the next 50-60 years in this area. The lag for natural regeneration of southern vegetation to repopulate areas with climate, weather or fire die-offs may take as long as 100 to 150 years if left to seed naturally.

“The most powerful tool to help our forests adapt will be the tree seedling bred for the specific environment, planted and cared for by the property owner. Genetically modified seeds are out of favour at the moment, but a technological fix may be important to enable trees to deal with stresses to come.

“In the past if you’ve ever planted a shrub you bought according to the plant hardiness chart and it didn’t live, blame the chart.” Stewart told us that the old chart was based upon the 1930 to 1960 records. “That period was so warm that the rating was off.” The new temperature and precipitation charts are more accurate.

To give an illustration of how the growing seasons have already changed, Stewart told the group that thirty years ago very little corn and soybean acreage was cultivated in Eastern Ontario.

He concluded on a note of caution: higher summer evaporation means a higher risk of fire for tree stands. He further qualified predictions of massive northward shifts of vegetation: “Trees can’t grow on rock.” He explained that if the soil isn’t there and the nutrients aren’t available, the species can’t get established, regardless of the temperature. A major problem with the northward march of the forest is permafrost, which isn’t receding as quickly as expected.

Perhaps the headline earlier this year was a bit optimistic when the writer predicted sugar maples would be growing along the shores of Hudson Bay within fifty years.

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