From Dogs: Not a Gardener’s Best Friend in the August 25 New York Times.
“The nitrogen in dog urine would seem to be a helpful fertilizer. In fact, the concentration of ammonium is often toxic to plants. ‘If you get one of these trees that every dog has to pee on, they can actually burn the bark,’ said Nina Bassuk, program leader of the Urban Horticulture Institute at Cornell University.
“Exactly how many dogs does it take to kill a tree? ‘That’s something that hasn’t been studied,’ Dr. Bassuk said. ‘And I’m not going to do it.'”
And from Gardening’s Final Frontier: the ‘Hellstrip’ in the September 1 Wall Street Journal, Nina has this to say:
“Nina Bassuk, program leader of the Urban Horticulture Institute at Cornell University, says gardeners should make sure that their hellstrip planting doesn’t interfere with established trees. Trees play an important role in urban areas, she says, for providing shade, mitigating stormwater runoff, and helping improve air quality. So be careful when shoveling near root systems.”