Weather Alert in Windham, Tolland, Hartford and Litchfield counties.
July 27

State Forests Weather Three Storms

Battered by three enormous storms in the past 14 months, with many thousands of trees damaged or downed, Connecticut trees and forests remain, improbably, reasonably healthy.

After last year's Tropical Storm Irene and the October snowstorm, and just days after Sandy lashed the state, foresters and forest scientists are once again assessing damage and estimating long-term impacts on the health of woodlands.

Incredible as it may seem, they say Connecticut forests weathered the three storms with far less damage than might be expected. That's surprising, because although Connecticut is often seen as a suburban state, it is 58 percent forested, with tree canopies often comparatively dense even in urban areas, making it vulnerable in major storms.

Roadside hardwood trees and ornamental hardwood plantings around homes tended to sustain the heaviest damage from the October snowstorm and Irene. With Sandy, it appears softwoods like pines and spruces were hardest hit.

After the two storms in 2011, damage to the 170,000 acres designated as state forest "was not as extensive as we expected, certainly not as extensive as roadside trees," said Christopher R. Martin, director of forestry at the state Department of Energy and Environmental Protection.

Foresters are still checking the damage from Sandy, but "interior forests, private lands and state agency lands, appear to have come away from this fairly unscathed," Martin said. Fairfield County forests may have sustained more damage than other parts of the state in the latest storm. An assessment there is just beginning.

Meanwhile, one prominent forest scientist said the heavy snowstorm last October that caused extensive tree damage in parts of Connecticut, including the Farmington Valley, was so extraordinary it was the kind of catastrophic event not likely to be seen again in many lifetimes.

"My guess is you are talking many hundreds of years for an event like that," said David R. Foster, director of Harvard University's Harvard Forest in Petersham, Mass., and an authority on the ecology and history of New England forests.

That is not to say that the Farmington Valley trees, for example, might not experience severe damage from a hurricane or some insect outbreak, but a similar snowstorm is unlikely to impact the same areas for centuries. Damage in the valley from Sandy was mild in comparison with the snowstorm.

Martin, the state forester, cited three factors that combined to produce heavy damage to roadside and residential trees during the snowstorm. First, last October was warmer than normal and trees held on to their leaves as much as two weeks later than usual, until the very end of the month, when the storm hit. The early fall snowstorm, with accumulations of 8 or more inches of snow in places, itself was extraordinary.

Moreover, roadside trees and residential trees typically have more room to spread their limbs horizontally, making them more susceptible to limb damage. Each leaf in effect became a platter to collect the heavy, wet snow until limbs could no longer bear the weight and snapped. Because many of those limbs had spread over utility lines in recent decades, the falling limbs knocked out power in vast areas of the state.

This year, many leaves were already on the ground before Sandy hit. In fact, Martin said, because hardwoods had largely lost their leaves, it left neighboring evergreens like pines and spruces more exposed to high winds, hence the reports of more damage to those softwoods from Sandy.

"The needles didn't allow the wind to pass through," Martin said.

While limb damage in state and private forests is considerable after the three storms, most trees retained more than 50 percent of their crown limbs and will recover, Martin said. Despite the damage, there was one benefit from the latest storm; many "hangers" — those limbs broken in the snowstorm last year but still dangling from tree canopies — came down during Sandy's high winds, reducing the risk of injury to people from falling limbs in coming months and years.

At least two mitigating factors were at work in the forests during the storms. In the forest, trees often grow in close proximity, which meant some snow-laden or wind-whipped limbs might have escaped damage because they were supported by a neighboring limb or tree trunk. More significantly, Harvard's Foster said, the very structure of forest trees in southern New England was a natural buffer.

"In the woods, the trees grow tall and straight with narrow crowns," making them far less susceptible to the impact of the heavy snow or high winds, he noted.

Jeffrey S. Ward, chief scientist in the department of forestry and horticulture at the Connecticut Agricultural Experiment Station, offered a rule of thumb for suburban trees. Those with less than 30 percent crown damage will quickly recover, though some will have more cavities in coming decades. Those with less than 50 percent damage will survive, but will not grow as quickly. Those with more than 75 percent crown damage will die.

Because both deer and invasive plant species are more common adjacent to developed areas than deep in a forest, it is likely that invasive species will increase in those suburban forests and roadside woods where tree mortality will be high, Ward said. Given an opening, the invasive plants seize the opportunity.

That has implications for people, Ward said, because feeding deer avoid some invasive species like barberry, which happen to provide favorable habitat for the tick associated with Lyme disease.

Meanwhile, the warming associated with climate change is expected to favor some species over others, and how a damaged forest is managed can affect how quickly tree species change, Harvard's Foster said.

With climate change, more southerly species will find Connecticut habitat increasingly suitable, while more northerly species will find it increasingly inhospitable. Foster said instances where a large area of forest is cut down because trees were damaged — as has happened in some forests since the October snowstorm — are an opportunity for forest change that otherwise would take place far more slowly.

Each time a forest is cut down, or leveled by a storm, it is a chance for new species to take hold, including an advancing southern species, for example. "That is where the selection process is going to take place," Foster said. "The more you impact forests, the more rapidly they are going to change."

At the Harvard Forest, Foster and colleagues began an experiment in 1990 in which a 2-acre section of mature oak forest was subjected to a simulated major hurricane, using a winch and cables to fell the trees. In a scientific paper just published in the journal Ecology, Foster reported that forests left untouched after a major disturbance recover more readily than if they are cleared.

While a forest may show evidence of the snowstorm damage, or wind damage, with downed trees and broken, hanging limbs still visible a year later, the forest will rebound nicely without any action, Foster said.

"Getting blown down, getting ripped apart, getting affected by outbreaks of insects is all part and parcel of being a forest," Foster said. "All those trees and all those other plants and animals that live in the forest are able to deal with those things.

"If what we are interested in is making a healthy forest, we actually don't need to do anything," he said.

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