This month, urban forestry concepts and lingo. Next month, why and how to think like an urban forester when selecting and caring for trees.
Life on the Streets
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 we humans can enjoy trees’ many benefits, like beauty and shade.
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. 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 particularly 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 10 years, there’s been a growing movement in urban forestry to put a dollar value on our urban trees based on their many tangible benefits, like energy savings. Community forestry groups are using free programs like the USDA Forest Service’s i-Tree suite of tools to assess the extent and value of their urban forests.
Using i-Tree, Brenda Cagle of Red Hook coordinated a tree inventory and analysis for the Town of Red Hook’s street trees. This was part of the Specialized Weekday Arborist Team (SWAT) project sponsored by Cornell Cooperative Extension (CCE) Dutchess County with funding from the USDA Forest Service and a NY Department of Environmental Conservation Urban and Community Forestry grant. It was completed in March 2013 by SWAT team members comprising forestry professionals, Bard College students, and master gardeners from CCE Dutchess County.
The team found that there are 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 has 855 street trees providing $109,304 in annual benefits, and in Cold Spring the SWAT team found there are 437 trees yielding $56,719 in annual benefits.
Brenda 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.
A Little Urban Forest 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 and planted without any machinery.
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: An increasingly popular 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, it won’t be so devastating to the total urban forest.
tree coffins, aka planting pits: These are tiny cutouts in pavement along city streets where most trees go to die young for lack of root space.
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.
Resources
Urban Horticulture Institute
i-Tree tools for Assessing and Managing Community Forests
This article appears in April 2014.
