This article was originally published in the Forests for Maine’s Future on August 26, 2014 and was written by Joe Rankin. View the original article here.

It’s perhaps fitting that the largest city in the most forested state in the nation should be nicknamed the Forest City. Of course, when Portland acquired that sobriquet, back in the 1800s, Maine and New England had a lot less forest.

Portland has thousands of trees. Large forested parks; small forested parks. Street trees by the hundreds. And a long history of nurturing what is known as urban forest.

Of course, in the beginning it wasn’t that way. Trees were initially felled for lumber, which became a big export item and helped the city prosper. But Portland planted its first tree in 1793 on Washington Avenue, and after the middle of the next century began a broader tree planting program. The city’s first tree inventory was undertaken in the 1860s.

Today Portland spends some $500,000 a year on planting and caring for its urban forest. City Arborist Jeff Tarlling supervises a staff of four full-time arborists and a forestry supervisor. Together they care for an estimated 18,000 trees: street trees and the trees in nearly a thousand acres of city parks, including coastal islands. And the city still plants some 200 to 250 trees a year and occasionally even harvests logs for lumber and pulp.

“It’s interesting to look back at the early city forester reports,” said Tarling. “One of the biggest complaints they had was if they could stop the horses gnawing on trees. That’s one of the things I don’t have to solve.”

People have planted trees and gardens in cities almost as long as there have been cities.

Today trees perform a host of vital functions in urban areas. They soften the hard edges of buildings, muffle traffic sounds, slow stormwater runoff, absorb pollution. They provide shade and reduce the heat sink effect of a city’s vast expanses of concrete and asphalt.

“They do a lot for making cities more liveable,” said Tarling. A city with a healthy population of trees tends to attact people, he said. That helps cut down on urban sprawl since people might otherwise eschew cities in search of a three-acre tract in the suburbs with a 45-minute commute.

But why are trees important in cities and towns in Maine, which is 90 percent forested, the state with the highest percentage of forest in the country?

Well, because that’s where the people are.

According to the Urban Forest Data for Maine published by the U.S. Forest Service’s Northern Research Station, 512,878 Mainers live in urban environments, though only 1.1 percent of the state’s land is classified as urban.

“Urban forest is the forest where people live. In a lot of cases people can’t get out and appreciate the vast forest in the rest of the state,” said Jan Ames Santerre of the Maine Forest Service, who manages Project Canopy, which provides grant funds to help communities bolster their street and park tree planting and maintenance efforts.

“They provide an aesthetic appeal to our communities that a treeless community doesn’t have. They have social values, environmental values and economic values, health benefits and numerous other values that people wouldn’t think of when they think of trees in the places where they live.”

Sometimes, she said, people don’t consciously acknowledge their attachment to urban trees, unless “they’re clued into that sort of thing.” That’s a mindset that those, like Santerre, have to constantly work to overcome. It’s almost as though many people take urban trees for granted, though they sure do miss them when they’re gone.

“People still talk about what Maine’s communities looked and felt like in the 1950s and 1960s” before Dutch elm disease laid waste to the American elms that provided a leafy splendor to towns small and large across much of eastern North America, said Santerre. “People want to re-create that look, but also the way a community felt back then,” she adds. “It’s really hard to describe what that does to somebody, but when people sit in a park surrounded by green, it relaxes them. It’s a good feeling and it provides a sense of community.”

But the benefits of trees go beyond the feel-good aspect. They are, literally, an investment in place.

Kathleen Wolf is a research scientist at the University of Washington who studies the human dimensions of urban forests. She has written that trees can help cut residential and business heating and cooling cost, boost occupancy rates in business districts, bump up customer traffic, increase commercial and residential real estate values, and boost home sales prices.

People like to see trees in retail areas, writes Wolf, who has studied public perceptions of urban forests all across the U.S.

“Trees positively affect judgments of visual quality, but more significantly, appear to influence other consumer responses and behaviors,” she wrote in a 2009 article on urban forests published in Main Street News. Surveys show people “favor trees in retail settings; this preference is further reflected in positive perceptions, customer behavior, and product pricing.”

But it’s important to note that people gave the highest marks to areas with a full, mature tree canopy, something that takes decades to develop, she said. Trees need to be looked at as a long-term investment.

“Trees and landscapes can be significant elements in place marketing,” Wolf writes. “Economists have noted that shopping was once a utilitarian activity to fulfill needs and wants, but today shoppers are pursuing places that offer social, memorable experiences. Trees help create place and connect to deeply felt preferences and appre- ciations that people have for nature.The urban forest is an important part of the vibrant, satisfying places that shoppers enjoy.”

The benefits of urban forests aren’t limited to large cities — smaller towns and villages benefit similarly.

And in addition to making downtowns and city residential neighborhoods more attractive places to live and offering concrete (pun intended) financial benefits to businesses and homeowners, there’s yet another reason for municipalities to invest in trees — they can help ameliorate the effects of climate change.

Cities are particularly vulnerable to rising temperatures since their concrete, steel and asphalt create a heat sink, and also are impervious to rainwater. In the northeast, where climate change is expected to increase the frequency and intensity of heavy rains, having trees around to help slow that runoff is a cost-effective solution and one with a bunch of positive side benefits.

Tarling said his staff is already planting trees with the idea of slowing stormwater runoff, which can overwhelm a city’s municipal sewage system and send untreated effluent into rivers, streams and the ocean, as part of a multi-pronged project by the City of Portland.

The Manomet Center for Conservation Sciences worked with the mid-coastal small city of Bath to try to get a handle on the value of the urban forest and the potential for trees to be put to work combating the effects of climate change, the so-called “ecosystem services” urban forests provide. Bath was intended to serve as a laboratory where the results could be applied to other small and mid-size towns across New England, said Andrew Whitman, the director of Manomet’s Sustainable Economies Program and one of four scientists who took part in the study, aided by the Maine Forest Service’s Santerre and Bath City Arborist Tom Hoerth. The four-year project was supported by a grant from the U.S. Forest Service, as recommended by the National Urban and Community Forestry Advisory Council.

Bath has 8,500 residents and more than 25,000 trees, according to a draft report on the four-year project. Those 25,000 trees are worth an estimated $10 million. Or, at least, that’s what it would cost to replace them. The city now views trees as fixed assets, like vehicles or fire hydrants. But Hoerth notes that there’s a crucial difference:  where vehicles depreciate, trees actually increase in value:  “The bigger the tree, the more benefits it provides, and those benefits, along with the tree’s financial value, grow over time.”

Manomet scientists worked with Hoerth and Santerre to put into dollars and cents the annual value Bath’s street trees yield to the city, using a computer program developed by the U.S. Forest Service called iTree. The analysis put that figure at $780,000 annually.

Bath’s trees remove 16,000 pounds of pollutants from the air, produce 626,000 pounds of oxygen, avoid 756,000 gallons of storm water runoff, and store over 1.4 billion pounds of carbon dioxide, according to the draft report on the project. Putting figures to those types of benefits can help bolster arguments for tree-planting and maintenance budgets.

The project confirmed the value of iTree as a way to quantify the value of a small town or city’s tree inventory, though some parts are more user-friendly than others, said Whitman. One other thing it showed is that northeastern municipalities are unlikely to be able to sell carbon credits on the offset market, at least  in the short term — their forests just aren’t big enough and the costs of participating are too high.

The project also looked how climate change is likely to affect small municipal urban forests in New England. Whitman said the project team concluded that, while urban forests would see changes over the next decades due to climate change, the urban forests are likely to be much more affected over the short term by introduced pests and diseases. Bath, for instance, faces the possible loss of 1,200 trees to emerald ash borer, a voracious introduced pest that has already decimated ash trees in the midwest and has been found in New Hampshire.

Urban forests can also serve as outdoor classrooms, teaching kids about the importance of forests worldwide. Earlier this year Portland thinned 12 acres of Pine Grove Park, a small park in the North Deering neighborhood, removing two loads of sawlogs and nine loads of pulp.

In late May 20 third graders from Lyseth Elementary School planted 300 white pine, black spruce and balsam fir seedlings there, a project underwritten by the Maine TREE Foundation (a Forests for Maine’s Future partner), Plum Creek Timber Co. and UPM Madison.

“We technically didn’t need to replant,” notes Tarling. “It was more about getting the students involved. They got to see the logging equipment and we had a demonstration.”

While the jobs of city foresters and foresters who work in forests elsewhere in Maine are, in their basics, remarkably similar, it should also be noted that people like Tarling and Hoerth face some unique challenges.

For the urban environment is not at all hospitable to trees. It can, in fact, be a particularly brutal landscape, especially for street trees. Horses may not be much of a problem these days, but there are plenty of others.

Chief among them is lack of space. Trees need space for their roots to reach out, and too often sidewalk-street greenspaces or “tree pits” don’t have as much as they really need. Space is at a premium in cities. Without the space, and the oxygenated, non-compacted soils, trees are slower to get established. Because their root systems are cramped they are more vulnerable to everything from high winds to drought. Pollution is a problem, road salt used to remove snow is toxic to many species, snowplows themselves can damage trees, and so can people who peel bark or carve their initials in it.

We ask a lot, particularly of street trees. Including that they have lacy, light foliage, grow quickly, look beautiful, and be the right size at maturity. Not just any species can meet those demanding requirements and is tough enough to stand up to the type of abuse street trees are called on to endure year in and decade out. Plus there are pests.

We’ve already noted how the blight of Dutch elm disease denuded thousands of American cities in a matter of decades. Sugar maples have proven to be less than ideal candidates for street tree spaces because they are susceptible to road salt poisoning. Emerald ash borer threatens all four species of ash found in North America. Then there is the Asian long-horned beetle, another import that has had a profound effect on the leafiness of several medium and large-size cities. The beetle, which finds a variety of hardwoods to its liking, was responsible for the removal of virtually every tree in some neighborhoods of Worcester, Mass. after it was found there.

Sometimes even the trees themselves become the problem. The Tree of Heaven, for instance, was imported to the U.S. from China in the late 1700s and widely planted as a street tree. It didn’t take long, however, for it to wear out its welcome:  the tree has a foul odor and a habit of suckering wildly. It’s now considered an invasive species.

Norway maples were widely planted as a street tree, but have since come into disfavor because they are considered an exotic invasive. Portland hasn’t planted Norway maples for 25 years, and is in the process of removing the ones that are there, said Tarling. Project Canopy won’t help pay to plant Norway maples, said Santerre, and it’s no longer funding the planting of ashes either, given the threat of the borer.

These days many urban foresters emphasize planting native trees. They’re already adapted to their environment and climate, so that’s one hurdle overcome. But, having learned a lesson in vulnerability with street tree monocultures, of elms, then later, ashes, they’re also emphasizing planting a variety of species.

“We’re trying to come up with a wide spectrum that can adapt to urban areas,” said Portland’s Tarling. “We’re trying use as many native trees as possible. That being said we don’t want to ignore non-native trees that do well in an urban environment either.”

Portland is planting lots of red maples, one of the eastern U.S.’s most widespread hardwoods. Portland is also planting oaks, hop hornbeams, hawthorns, American larches, sassafras; pitch, red and white pines; spruces, and gingkos. It’s experimenting with an English-white oak hybrid named “Crimson Spire” and out some disease resistant elm cultivars like “Princeton.”

Project Canopy’s Jan Ames Santerre said municipalities want to avoid trees that are invasive or that aren’t recommended for a particular area’s hardiness zones.

“There are a lot of different kinds of oaks that are useful,” she said. “There are dozens of smaller-stature trees appropriate for smaller spaces such as crabapples, cherries, hawthorns, Japanese tree lilacs. There are some different varieties of disease resistant elms as well.”

Communities should look at the source of the stock, since different nurseries can have stock with different genetics. “When you’re looking for trees, look for differences in shape, structure and canopy and different kinds of flowering,” she said. “Think about what the tree will look like in 30 years.”