Grounds staff run an intensive tree-care program, says Grounds manager John Reinhart, but despite their best efforts, pollution, temperature extremes and repeatedly hot, dry growing seasons have taken their toll on the most vulnerable trees on campus.

  "Some trees have been stressed to the point that they become easy targets for diseases that can ultimately kill them," says Reinhart. "And affected trees will have to be replaced sooner or later. It's never an easy decision to cut down a tree, and we are doing everything possible to avoid replacement, but dying trees become structurally weak and are a safety hazard during severe weather conditions. And the longer we wait to replant affected trees, the more compounded the problem will get."

  Walkways, roadways and courtyards embellished with mature trees have always been one of the University's renowned trademarks, but these are the most challenging areas for trees to survive in, says Reinhart. Many trees are suffering from heat stress largely due to the enormous amount of light and heat reflected on to trees from buildings and walkways, especially when temperatures climb above 30 C. Hard surfaces restrict oxygen from getting to root areas and excess water from getting away. In addition, high levels of carbon monoxide are showing up in trees lining roadways. This is a chronic problem in front of the University Centre, where vehicles are known to idle for extended periods.

  Specific tree varieties and areas have been stressed more than others, says Reinhart. The silver maples that frame the conservatory gardens and the roadway in front of the University Centre are suffering from heat stress and environmental pollutants. Ten to 15 sugar and Norway maples are replaced each year along Winegard Walk for the same reasons.

  The shade master locust trees that line the west to east walkways, especially in the area north of the Richards Building and south of Raithby House, have fallen victim to ganoderma, a vascular disease transmitted through intermingled root systems. It weakens the cellular structure in trees, stunts their growth and leaves them susceptible to pestilence. Such was the case in 1994 when the tarnished plant bug defoliated the locust trees.

  Because of their deteriorating condition, the silver maples and locusts are the first trees scheduled for replacement, along with a number of birch trees in various locations that were severely damaged by last fall's drought and a dry spring, says Reinhart. Removal of the dying trees is slated to begin in early to mid-October, and replanting should begin in late October.

  Other trees under consideration for future removal include the London plane trees lining various ring roads, because these trees have been splitting due to their susceptibility to severe cold and frost, he says.

  The trees will be replaced with more stress-resistant varieties such as oak, green and white ash and linden. "We already have stress-resistant varieties of four- to six-inch caliper (trunk width) growing in the Grounds nursery, so the cost of replacing the affected trees will be minimal considering what's at stake," Reinhart says.

  He believes this fall is an opportune time to rethink tree-planting practices at U of G. "By recognizing and dealing with the problems we have now and taking proactive steps today, we can ensure a safer and healthier landscape tomorrow."