April 2,1998

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Geography Professor David Greene studies forest regeneration

Trees are more resilient than we think

by Tracey Arial

Our forests will have regenerated from the recent ice storm in about five years, says Geography Professor David Greene, and in 75 years, the damage won't even be noticeable.

"Tree species found in the primary ice-storm belt (Wisconsin east to New Brunswick) would not persist here if they were unable to adequately regenerate the openings created in the forest by the death of the branch-stripped trees," Greene wrote in a recent article.

His opinion has received a lot of attention lately, not just because people want to believe the trees will recover, but because he is one of the few people who has studied the results of previous ice storms.

Although Greene specializes in forest regeneration, most of his work so far has concentrated on regeneration after fires or clear-cutting. It's a natural focus, since Greene was born and educated on the west coast, where clear cuts and fires devastate forests all the time.

But ice storms didn't interest Greene until he came to Concordia as a lecturer in 1988. His search for an old-growth forest near Montreal led him to Mont St. Hilaire, a UNESCO Biosphere Reserve 35 miles east of the city. It was there that he began to wonder what kills mature trees.

"You go to an old-growth forest like St. Hilaire and you find out there aren't that many older trees," Greene said. "The canopy there is between 100 and 250 years old. You get a few trees that are 400 years old, but they're incredibly rare."

In boreal forests, found in British Columbia, the only severe natural threats to trees are fire and budworm. But here, mature trees in eastern forests are thought to die from insects, fungus, wind storms, ice damage, and a bit of everything.

Greene identified several gaps in the canopy while on Mont St. Hilaire, and discovered that most of them were due to an ice storm in 1983.

"I realized that the ice storm of '83 took out about 10 per cent of the canopy," he said. "So I began to think that if ice storms recurred a few times each century, and if each time about 10 per cent of the canopy trees were killed, then that would implicate ice storms as the major killer of mature trees."

To prove the hypothesis, however, he needed more information. For instance, he needed to know how often ice storms of a certain magnitude occur. Hydro-Québec has been collecting such records for the past 25 years, and Greene hopes to take advantage of them as his research progresses.

The next steps are more difficult, though. Greene needs to determine how much ice collects on branches when a certain amount of ice falls to the ground, and what the chances are of a particular branch breaking under such pressure. For that, he needed data during another ice storm. That's where January's storm was supposed to come in.

"I know now why there isn't much research about the direct effects of an ice storm," Greene said. He tried to go to Mont St. Hilaire several times during the week of the storm, going so far as to buy a car. In the end, bridge closings, ice damage and the lack of electricity kept Greene in
the city.

That's when he got his students involved. About half of the volunteers took measurements on Mount Royal while others measured urban trees.

Their help was invaluable, but Greene still doesn't have quite enough information to prove his ice storm hypothesis. That should change this summer, when Greene participates in the Groupe de Recherche en Écologie Forestière. He and researchers from the three other Montreal universities will be studying damage left by the January ice storm. They want to make a connection between branch loss and tree mortality.

Greene studied at Berkeley, California and then followed an adventurous streak to Canada. He completed both his Master's and PhD at the University of Calgary.

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