[getsmart-l] DROUGHT: Paying the Price - To turn squirrels into tree killers, just subtract water

[John O'Gorman]

Any similar stories in your area? Are there even worse prices-to-pay in your area?

Also, more support for under-storey/multiple-aged trees!!-
"and there aren't a significant number of middle-aged trees coming up to replace them," Dr. Millward says."

http://www.theglobeandmail.com/servlet/story/LAC.20070915.WATER15/TPStory/?query=trees
DROUGHT: PAYING THE PRICE

To turn squirrels into tree killers, just subtract water
DALE DUNCAN 

Special to The Globe and Mail

September 15, 2007

Toronto's trees have had a tough go of it this summer. After three months plagued by drought, many are struggling to stay alive, and the sugar maples that grow among nearly 250 trees in Allan Gardens are no exception. 

But for many of these sugar maples, the severe lack of rain is the least of their problems. The bigger threat: a growing gang of thirsty squirrels who call Allan Gardens home. 

"This place is like a desert for wildlife - especially those who can't or don't leave the park," says geographer Andrew Millward, who has been conducting research in the park over the summer with his graduate students from Ryerson University. In August, he noticed that the park's squirrel population, lacking access to water, had started tapping the trees, stripping the bark to get at the sugary sap that flows underneath. 

Since the park is surrounded by four busy streets (Jarvis and Sherbourne to the west and east and Carlton and Gerrard to the north and south), leaving the park to search out other sources of water or food is like playing real-life Frogger, a risk squirrels aren't likely to take.

Their cravings mean that many of the park's medium-sized trees, some close to 40 years old, could be dead by next spring. A few branches have been completely stripped bare, making them vulnerable to disease and insects. "It's similar to a person walking around with open wounds," Dr. Millward explains, looking up at the branches of one particularly wounded tree growing east of the park's conservatory. 

He points out pieces of bark on the ground around the tree - just debris to the squirrels. They are trying to get at the xylem and phloem, the layers under the bark that contain the vessels that carry sweet photosynthetic materials from the leaves and water from the ground. Without these vessels, a tree can't transport the nutrients it needs to grow.

"I can foresee that next year, come spring, people will be horrified by the number of dead and dying trees," Dr. Millward says. 

Dr. Millward believes the fact that this has been the driest summer on record has played a role. Rainfall data collected by his research team shows a measly 7.6 millimetres fell last month. According to Environment Canada, the average rainfall for downtown Toronto in August is 79.6 millimetres. 

The city does not irrigate the park or run any form of water - a fountain to the west of the conservatory remains dry, while greenery is growing out of cracks in an aging wading pool to the south. The city's watering program applies only to newly planted trees, which means the mature trees in Allan Gardens are not watered. 

Toronto's head forester, Richard Ubbens, says an unusually large squirrel population is largely to blame for the wounded trees. "You do get years where the squirrel population blows through the roof," he says. He says these often follow mild winters, which are less likely to kill off young squirrels or present much of a challenge for finding food. "Probably the last time it was this bad was in '91, '92," Mr. Ubbens says.

Such complications, he adds, are part of the job. "Managing the urban forest means considering all the living things that it sustains - it's not just trees."

For many of the sugar maples in Allan Gardens, however, it may be too late. "Many of the older trees here are likely not going to be with us for much longer, maybe a decade at the most, and there aren't a significant number of middle-aged trees coming up to replace them," Dr. Millward says. "These sugar maples are the middle-aged trees. Unfortunately, their chances of survival are slim." 
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