Mighty oaks from little acorns? Not if this scientist can help it Arboretum expert keeps city trees small for their own good

When it comes to trees, bigger isn't always better.

In urban settings, where space is precious, trees might quicklyoutgrow the spot where they were planted. Those located underneathpower lines, for instance, might have to be cut back again and again,leaving a brutal "V" chop in their upper branches.

Gary Watson, senior research scientist at Morton Arboretum inLisle, is looking for ways to keep tree growth from getting out ofhand.

"In the city, a tree may have a very small root space, sitting ina little cutout in the sidewalk," Watson said. "Its lifespan may beonly seven years, while, in a woodland, it might go on for hundredsof years.

"If we can slow it down, it's still not going to be a 100-year-old oak tree. But it may only have to be replaced every 14 years orevery 20 years."

There are two ways to slow tree growth -- chemical and physical:

*Chemicals with trade names like Cambistat and Profile areinhibitors of gibberellin, a hormone that stimulates cell expansionto produce larger leaves and longer shoots.

"It's not very attractive if you overapply it," Watson said. "Youget what is described as a 'poodle tree.' "

*The alternative includes pollarding -- cutting the tree backalmost to its stump and pruning shoots to a desired length. InEurope, some pollarded trees are as much as 500 years old, Watsonsaid.

Japanese bonsai trees -- "tabletop trees" -- can live even longer.Their growth is controlled both above and below ground. Plant-tenders pull them out of their pots and prune the roots.

At the arboretum, Watson is experimenting with more than 200trees.

"They're mostly oaks because that's what we have here," he said.

One finding: A side benefit of treatment with a growth regulatorkills apple scab, a disease that strikes crabapple leaves.

At his home in Naperville, Watson has a honey locust tree that'sjust large enough to shade his patio -- but still growing. So heprunes it.

"If it gets too big, it's the beginning of the end for that tree,"Watson said.