It's the season of the trees. After all their hard work keeping things green and cool this summer, deciduous trees are putting on their final performance of the year. Now, while they're flaunting their finest costumes, is an appropriate time to take stock of what trees do for us. It is also a good time to plant new trees for the generations to come.
We appreciate trees for their magnificence and beauty through the seasons, but it's easy to forget all the ways they contribute to our quality of life. A handsome tree in the front yard makes a house a much nicer place to come home to. Oaks, maples, lindens and other deciduous trees lining city streets shelter whole neighborhoods and fill them with character. Trees mark ancient trails and punctuate contemporary landscapes, subtly defining our view of the world.
Trees are one of the most massive elements of our environment. In the process of photosynthesis, they remove carbon dioxide from the air and replace it with oxygen. Their extensive root systems filter the water in the soil. Trees provide food and shelter for wildlife, especially birds and the insects they need to survive. Without trees, the world would be dreary and inhospitable.
With increasing urgency, arborists and urban foresters are studying trees in cities, public gardens, parks and the countryside to try to determine which trees are the most adaptable to changing climate conditions, including extreme weather events such as droughts and flooding. The Chicago Botanic Garden started its Trees for 2050 project specifically to help the garden decide how to replace about 400 trees recently lost to infestations of the emerald ash borer. Of 50 different kinds of trees at the botanic garden, the study found that 40 of the native and well-adapted exotic species remain good choices until 2050, says Phil Douglas, curator of woody plants at the garden. By 2080, as the climate continues to change, only 11 of the species in the initial study will continue to thrive in Chicago and the Upper Midwest, he says. The Garden's research resulted in an interactive online database to help residents of Chicago -- and throughout the Midwest -- make the best choices for their home gardens.
Gingko, pecan, zelkova and parrotia trees are among the most adaptable and viable trees for the long term in the Midwest, Douglas says, but these trees are just a starting point. Much more work needs to be done to identify the best trees for the Midwest's changing climate, and for every area of the country.
Shawn Kingzette, an arborist with the Davey Tree Expert Company and a regional manager for the company in the Chicago area, recommends diversity, above all, to help ensure a future with healthy trees. "It's not enough to plant native trees that can resist bugs and blights," he says. "Natives are susceptible, too." A diverse tree population provides resilience, Kingzette says -- so if you love dogwoods or redbuds, plant one, by all means, or even three, but not a dozen of them in your home garden, or you risk losing your whole planting. Urban foresters learned this the hard way when elm blight drastically changed urban landscapes years ago. The emerald ash borer infestation has reminded them again, vividly, of the possible consequences of over-reliance on a single species.
Careful planting -- avoid planting under utility lines and too close to houses, sidewalks or driveways -- will also help ensure that trees have a long and healthy life. It is important to choose trees that fit their spot, Kingzette says. A small tree, such as a fringe tree, is likely to be a more appropriate choice near a patio than a towering oak. Sweet gum trees, with their prickly fruits, are great habitat trees, but don't plant them near a sidewalk.
A warming climate will expand the choices in colder areas, allowing warm-zone trees, such as crape myrtles, to thrive farther north, but "don't just plant southern species -- plant tougher species," Kingzette suggests. Turn to your local horticultural extension experts for their recommendations.
If you're planting a tree, consider planting on the south or west side of your house, where a deciduous tree will keep your home cooler in summer and allow the sun's warming rays through in the winter, to save on utility bills. Three trees placed strategically around a house can save up to 30 percent on energy bills, according to the U.S. Forest Service. Small trees that shade air-conditioning systems help the units cool more efficiently.
Fall is an excellent time to plant deciduous trees, which take advantage of the cooling season, even after their leaves have dropped, to establish healthy root systems. Trees planted in fall will get off to a good start in spring because their roots will already have reached down to moisture deep in the soil. Larger specimens may not show much top growth their first year or two, but they are adapting to their new circumstances. Water well after planting, once a week if necessary (until the soil freezes, if you're in a cold climate), while trees are becoming established.
Even small trees make a significant contribution to any landscape, with spring blooms, pretty summer canopies of leaves, rich fall color and lovely, sculptural shapes in the winter. Berries and nuts feed birds and squirrels through the winter. Trees also have economically tangible yields: Online tree-benefit calculators let you type in the kind of tree you have, its size and your location, to determine the monetary value of trees and remind you that curb appeal -- and property values -- go up when pretty trees are part of the picture. Plant now, and when spring comes, you can give yourself plenty of credit for a wise investment, the returns on which are actually far greater than the cash calculators can project.
-- For more information about the Chicago Botanic Garden's Trees for 2050 project, including a list of trees, go to: chicagobotanic.org/plantinfo/tree_alternatives
-- The Arbor Day Foundation has tree-planting tips and information about trees and climate change: arborday.org/trees/climatechange/fightHome.cfm.
-- To calculate the value of trees in your garden, try one of the tree-benefit calculators listed on the Holden Arboretum's website: holdenarb.org/horticulture/calculate-the-value-of-a-tree/
-- The Davey Tree Expert Company is a national company of arborists and tree experts, with residential and commercial services: davey.com.