Of the estimated 1.1 million trees that line Connecticut's streets and highways, as many as 620,000 are large enough to pose potential hazards to utility lines and roadways during future storms.

Of those 620,000, more than half are maple trees that, because of their growing habits, tend to have structural defects such as hollow cavities and split trunks with weak forks that are most vulnerable in high winds and heavy snows.

Pre-emptively removing all the large maples growing along state and municipal roadways would cost $185 million or more. Given the expense, state and municipal tree caretakers should instead consider evaluating the condition of all maples and other trees near power lines that have trunks one foot or wider in diameter - the size determined to be most susceptible to storm damage.

Those are some of the findings of a preliminary analysis of the state's urban forests done by Jeffrey Ward, chief scientist in the forestry and horticulture department at the Connecticut Agricultural Experiment Station.

It is the first report to quantify the risk posed statewide from large street trees as the state seeks ways to prevent the kind of prolonged power outages and extensive damage that resulted from trees felled during Tropical Storm Irene in August and the Oct. 29 nor'easter.

Completed this week, Ward's report was done at the request of the Department of Energy and Environmental Protection as part of the post-storm analysis and response. The report has been sent to Gov. Dannel P. Malloy's Two Storm Panel, which met Wednesday.

"Maples are fabulous shade trees because they're very fast growing," Ward said, explaining why maples became the dominant Connecticut street tree. "But because they grow so fast, they don't have the defenses. What grows fast dies fast."

For his analysis, Ward extrapolated tree data from 11 cities and towns that had conducted recent tree inventories to estimate the potential risk statewide of tree damage during extreme weather events. Among the towns were two in southeastern Connecticut: Colchester and Essex. In Colchester, there are 218 large-diameter trees of the 232 along town roadways, the report said. Essex has 1,371 large-diameter trees of the 1,415 along its roads.

To minimize future outages, Ward recommended that the state Department of Transportation and municipalities plant only varieties of trees with mature heights not exceeding 30 feet and keep trees no closer than eight feet from power lines.

He recommended against removing all street trees, calling this a "drastic solution" that would "inexorably alter the sense of place characteristic of Connecticut's towns and cities. The resulting cityscapes would be devoid of nature except for patches of grass and scattered flower beds."

Instead, planting smaller trees "would preserve the benefits of ... an urban tree canopy including reducing personal stress, cleaning air, reducing heating costs, reducing storm water runoff and sequestering carbon dioxide," he wrote.

Chris Donnelly, urban forestry coordinator for DEEP, said Ward's report will help guide the Two Storm Panel as it develops recommendations about how the state can minimize its risk of future storm damage and outages.

Ward's findings will also be shared with state and municipal officials who make decisions about which trees to plant along roadways, Donnelly said.

j.benson@theday.com