After a consistently rainy October and November, foresters across the north suburbs are cautiously optimistic that trees will continue recovering this winter from two years of dry conditions, and will flourish in the spring.
The summer of 2012, one of the driest on record, combined with the cool and dry summer 2013, had experts saying that northern Illinois trees needed a consistently rainy fall to recover from over 18 months of stress, which left them susceptible to the ravages of insects and disease.
An overly wet spring of 2013 proved too much of a good thing, suffocating root systems, diminishing their capacity.
"A wet fall is something we're looking at with great interest," said Gilbert Sebenste, head meteorologist at Northern Illinois University in DeKalb. "Now we're getting back close to where we are supposed to be on rainfall."
In winter, good moisture is measured in snow cover, keeping root systems moist, but not soaked, and ground temperatures moderate, Sebenste explained.
"As we head into December and storm systems move through, they draw a lot of cold air down from the arctic circle," he said.
"We know people don't want to see a lot of snow this winter, but for the sake of vegetation and trees, we do want that," Sebenste said. "The chances of drought this winter are starting to decrease and that's good. Northern Illinois has been moisture-starved the last two years."
Deerfield Arborist Eric Oscarson agreed.
"I think this constant, consistent rainfall is definitely helping, especially going into the dormant period of winter," he said. If the trend continues, "We expect the trees to come bounding back from good snow cover by spring."
"Last year's spring was overly wet and too much rain. Like any other plant, if you throw too much water at it, you can have adverse effects. In essence you're drowning the tree."
Northbrook Village Forester Terry Cichocki said she's already noticed good signs from recent weeks of steady rain.
"We're looking for winter buds to get plump because of the rain and see the bark 'popping,'" she said. "It's the fall when trees put out most of their roots. We have to look at trees not only from the ground up, because half the maladies are in the root systems.
"We need regular snow through the winter, with not a lot of melting. It doesn't have to be snowing like gangbusters, like with blizzards, just an inch or two on the ground for at least two months. Snow is at a constant temperature, 32 degrees. With snow cover you are less likely to get soil temperature fluctuation, which causes root freeze and damage."
Village of Winnetka Forester Jim Stier said property owners don't have to rely entirely on Mother Nature.
Stier recommends people water trees and shrubs "right up to Thanksgiving, especially the evergreens, which store, and can lose, moisture through their needles. Two to three inches of mulch also helps insulate the root systems. Chicago Botanic Garden and the Morgan Arboretum recommend mulching out to the (trees') drip line," he added.
Ecologist Chip O'Leary of the Cook County Forest Preserve District — with more than 40,000 acres of trees — said the steady, measured rainfall in recent weeks has been "recharging the water table. It's come at a rate where the soil is still absorbing. it's not puddling up and running off.
"If all goes well, the rains and coming snow cover will recharge the ground water level and have root systems in good condition when the trees pop out of dormancy next spring," he added.
"The summer of 2012 drought's effects will be felt for years to come, especially with a lot of root damage and stress on the trees," said Mark Cinnamon, the state's plant regulatory official for the Department of Agriculture. "But I think the rain in the past month, especially, will definitely help the trees going into next spring."
Illinois is one of the top tree-nursery states, with about 800 in the 12 northeastern counties of Illinois, Cinnamon explained.
"We inspect all the nursery stock that's grown and offered for sale in Illinois and we're very aware of the weather conditions," Cinnamon said. "If we have no sudden, huge temperature swings through the winter, a lot of trees will do well. We've had two to five inches of rain the last two to three weeks in the upper two-thirds of Illinois."
Tom Smith, stewardship coordinator for the Lake County Forest Preserve, said mulching with wood chips around the base of trees and shrubs will ensure better survival rates.
"Mulch holds the moisture in and keeps the weeds down and over time it fertilizes it as well," Smith said. "Trees can handle a lot of stress, especially in the really bad years, like 1988 and '89, when it was super-hot. The trees rebounded when they got some water."