Contributed by Nancy Stedman

Acer saccharum (sugar maple)

“Trees are not so different from us humans,” says Jason Lubar, Associate Director of Urban Forestry at the Morris Arboretum of the University of Pennsylvania. Like people, they prefer to congregate in communities, can spread news quickly (via biochemical processes) and often give each other a helping hand (by, say, sharing nutrients with an ailing neighbor). There’s a growing conviction among some scientists that trees are “sentient beings,” in the words of Lubar’s colleague Robert Wells, Associate Director of Arboriculture Outreach at the Arboretum. “Trees,” he explains, “are aware of temperature changes, and changes in water and soil. In some ways, they can see and smell.” This nuanced view has recently gained currency among the public through a wildly popular book called The Hidden Life of Trees: What They Feel, How They Communicate. Written by a German forest manager with an academic bent, this surprise international bestseller details how trees navigate the world without being able to move.

"Anything that leads to feelings of kinship or connection helps people appreciate trees more"

"Anything that leads to feelings of kinship or connection helps people appreciate trees more", Lubar says. And that makes the jobs of Lubar and Wells much simpler. “At the Arboretum, we try to educate people about the value of trees,” says Lubar. The two certified arborists, who are part of Morris Arboretum’s Urban Forestry Consultants team, can easily rattle off numerous practical benefits. Trees, in addition to providing beauty to the landscape, moderate air temperatures, sequester carbon, reduce storm water run-off, lower air pollution and support wildlife. There are financial considerations, too. Planting trees in your yard enhances property values—the accepted figure is a jump of about 10%. Also, simply being in the presence of trees can boost your well-being by lowering stress hormone levels and boosting your immune system, according to recent research. “Trees provide benefits well beyond their costs, so it behooves us to have more of them,” Lubar says.

Liriodendron tulipifera (tulip poplar)

Trees are especially important for the health of American cities. Although Philadelphia is one of the greener urban spots in the U.S., Lubar and Wells believe that its tree canopy should double, from 20% to 40%. Incidentally, the tree types you’re most likely to spot in Philadelphia are black cherry, ash, and the invasive ailanthus, a.k.a. tree of heaven; together, they make up a quarter of the tree population. Not surprisingly, the most tree-deficient parts of the city are the most built-up: Center City, South Philly and North Philly. “Most trees here are in parks,” Lubar notes. “They should be better distributed—more should be planted on streets, private land and school yards.”

Simply being in the presence of trees can boost your well-being by lowering stress hormone levels

Ecology-wise, what are the best trees to plant? “Large-maturing, deciduous trees, mostly native,” answers Lubar, who points to white oaks, tulip poplars, sugar maples, and hickories (if you can stand the falling nuts). “The benefits from large trees are huge!” Wells adds. He cites one project the Arboretum was involved with. “In 2009, we consulted for landscape architects who were working on Shoemaker Green, which is outside the University of Pennsylvania’s Franklin Field.  There was a grade change, and we helped protect six mature London plane trees, with an average diameter of 24 inches. We ran some calculations on these six trees, and learned that they provide the same environmental benefits of 1,300 two and a half inch-caliper trees.” Yes, that number is 1,300.

While large trees are the most beneficial, homeowners tend to gravitate toward small ornamentals such as dogwoods and redbuds. “They’re nice, they’re easy to see, and they don’t block vistas,” Lubar says. “It’s a challenge to get people to plant large trees.” The native vs. non-native issue is another area in which ecological and aesthetic goals can be at odds. “There’s no question natives are better in terms of supporting native wildlife such as birds and bees,” says Wells. But non-natives can really expand your plant choices, if, for instance, you want an evergreen screen in your yard.  “As long as non-natives aren’t invasive and they perform their landscape function, that’s okay. But try to make native trees a larger part of your garden,” Lubar suggests.

Remember that when you plant a tree, you’re entering into a long-term relationship. Make sure this is a creature you can live with—and maybe even become simpatico with.

Freelance writer Nancy Stedman is a Philadelphia Tree Tender.