Urban Forestry Fundamentals, Part 1: Concepts and Terms

Part 1 introduces Urban Forestry concepts and terms. Part II covers why and how to think like an urban forester when selecting and caring for trees. Written by Michelle Sutton 

Broadening Notions of “Urban”  
Forestry is managing woodlands for enjoyment, ecosystem health, and wood products. Urban forestry is getting trees to grow in inhospitable environments, like along city streets, so that humans and wildlife can benefit from trees in their daily lives.

In this context, urban means significantly altered by human activity. So college campuses, parks, and even your yard are urban settings, and they are all stressful for trees. Cornell Urban Horticulture Institute Director Nina Bassuk, an expert on street trees, explains why.

“Among the landscapes in which we live,” she says, “the soil has been disrupted and probably significantly compacted, which reduces oxygen, nutrient, and water availability to tree roots. Heat is reflected off of buildings, paved surfaces, and cars, putting more water stress on plants. Deicing salts used on paved surfaces can reduce water uptake by plant roots and cause toxic symptoms. Tree roots that are in the vicinity of pavement and structures often have limited soil volume to explore.”

Small, newly planted trees in the urban forest are sometimes subject to the further indignity of vandalism. They are extra vulnerable to drought, weed competition, and damage by mowers and string trimmers. It’s rough out there for mature trees, too. In parks or even alongside your driveway, notice the state of the trees that are closest to foot or car traffic. They will often show signs of stress, like dead branch tips, because their roots have been compacted.

Interventions for Our Trees  
Urban forestry gives us tools to analyze a site and then match the right tree to the particular conditions of that site. It asks, what are the toughest tree species for these stressful conditions? How can we best prepare the site before we plant the tree, and what is the best way to plant? How do we best care for them in the delicate first few years of establishment, and all their lives?

Why go to all this trouble? Trees make our urban environments livable. They provide beauty, psychological comfort, and energy-saving shade; they calm traffic; they take carbon dioxide out of the air and sequester it as carbon in their wood; their canopies slow down stormwater runoff so that municipal drainage systems are less taxed; they are proven to improve property values; and they provide food and shelter for wildlife.

In the last twenty years, there’s been a growing movement in urban forestry to put a dollar value on our urban trees based on their many tangible ecosystem benefits, like energy savings. Community forestry groups are using free technology like the i-Tree suite of tools to assess the extent and value of their urban forests.

Using i-Tree, Council Board Member Brenda Cagle of Red Hook coordinated a tree inventory and analysis for the Town’s street trees in 2013. The team found that there were 450 trees on public land in Red Hook that provide $70,661 in annual benefits, or $157.02 per tree. She and the team also inventoried Beacon, which had 855 street trees providing $109,304 in annual benefits.

Cagle says, “Communities are usually surprised to learn the dollar value of the benefits provided by trees. They see how important it is to preserve this resource and often change their funding priorities. Most small municipalities perform only one type of tree maintenance— removal. But after the inventory results are in, they begin to think about properly managing the forest to keep it healthy and safe. The urban forest has been described as the only infrastructure whose value increases over time, making its management a wise investment.”

For practical reasons, these and most inventories are done exclusively on public trees. Yet, the urban forest is actually made up of all the trees, public and privately owned, within a municipality. Though the term “forest” may be misleading, it was coined because the focus of urban forestry has always been the benefits (energy savings, etc.) that can be realized from the collective urban canopy.

An Urban Forest Mini-Glossary

balled-and-burlapped trees vs. bare root trees: Trees whose root balls come in a ball of soil wrapped in burlap are super heavy to transport and often require backhoes or other equipment to plant. More communities are going with bare root trees, because they are cheaper and much lighter to transport and thus more volunteer-friendly—they can be carried by hand and planted with just a shovel.

certified arborist: In the arboriculture field, the International Society of Arboriculture (ISA) Certified Arborist designation is widely regarded as an important mark of professionalism and essential knowledge.

city forester / urban forester / municipal arborist: Though duties can vary from city to city, these job titles are more or less synonymous.

community forestry: A growing model wherein citizens and nonprofits partner with government to strengthen the urban forest.

cultivars: The word “cultivar” is a mash-up of “cultivated variety.” For instance, ‘Karpick’ (cultivars are always indicated by single quotes) is a cultivar of red maple. Cultivars are selected or bred for ornamental qualities or the ability to withstand certain stresses. ‘Karpick’ is much more narrow than the regular red maple, so it could work better in a tight urban space. If you wanted a red maple cultivar that holds its blazing red leaves late into fall, you might pick the cultivar ‘October Glory’ for that trait. There can be dozens of cultivars of a given tree species.

monoculture: What got us into trouble when Dutch elm disease infected American elms. Whole neighborhood, even citywide, tree canopies were decimated. Now urban foresters maximize biodiversity in their tree inventory so that if any one species is infected with a new disease or decimated by a pest, it won’t be so devastating to the larger urban forest.

tree lawn: The strip of grass between the sidewalk and the road that is owned and often planted with street trees by your municipality. If you get a hankering to plant trees or anything else in the tree lawn, it’s a good idea to consult with your urban forester first. 🌳