Remember the old adage about the man who knows the cost of everything but the value of nothing? Many of the most precious things in life — fresh air, natural beauty, cohesive communities — are given short shrift in decision making because they cannot easily be assigned an economic value.
Trees, of which our city is duly proud, are a perfect example. They deliver a host of benefits to our community. At a time when the earth is getting hotter at an alarming pace, they cool our city, reducing energy spent on air conditioning. They sequester carbon dioxide, a major cause of global warming. They remove particulates from the air we breathe. They retain precious water in the soil. They moderate the force of winds that blow in from the desert. Trees shade and cool our roadways, slowing the deterioration of asphalt and reducing repaving costs by as much as 60 percent.
Tall trees transit the borders between the natural world and the built environment, connecting us to the broader ecosystem. They provide habitat for wildlife, especially raptors like hawks and owls that are essential to keeping rodent populations in check.
Trees have important psychological and health benefits. Studies have shown that merely looking at a tree improves rates of recovery from illness. Students have greater success in school when their home study area provides a view of trees. Trees give us "peace and quiet," reducing ambient noise, like the roar of the 10 and 210 freeways.
For all of these reasons, trees have a positive effect on property values, increasing them by as much as 10–15 percent. Consider the attractiveness of a tree-shaded home or a tree-lined street and you quickly understand why our "city of trees" is a desirable place to live.
Measuring for better management
While positive qualities of trees have been appreciated for many years, trees are often regarded as "amenities," whose benefits are difficult to quantify. As a result, when the hard costs associated with the care and maintenance of trees are compared to the "intangible" benefits they confer, hard-nosed managers are inclined to make "tough decisions," and valuable trees are often removed in the name of sound fiscal management and cost efficiency.
Managing for sustainability requires us to seek enduring solutions that support the environment, the economy and social equity, sometimes referred to as "the 3 Es." Most management outcomes are measured in dollars. So in order to compare the merits of our decisions in all 3 realms, it would be helpful if we could measure environmental and societal effects in dollars, too.
Can we ascribe an economic value to trees?
Tree appraisal systems have been widely used since 1951, when the Council of Tree and Landscape Appraisers (CTLA) published the first edition of its Guide for Landscape Appraisal. Since then, methods of tree appraisal have evolved. Today there are more than 30 software packages developed for efficiently managing tree inventories and valuations.
Originally focused on "trees as property" — useful in real estate appraisals and litigation — tree appraisal systems have broadened their scope to include the environmental and societal impacts of trees. i-Tree, an open source software system released by the USDA Forest Service in 2007, calculates the asset value of a tree based on its annual benefits for energy conservation, air quality improvement, CO2 reduction, storm water control, property value increases and aesthetic value. It also incorporates GIS mapping and a phone-friendly application for mobile data collection.
How Much Is a Tree Worth?
Some trees have particular local significance. In 2010, when a company installing a traffic signal irreparably damaged the Dutch Elm at Indian Hill and Tenth Street, the City collected a settlement of $79,000, based on the tree’s appraised value. Ordinary trees are worth less, but it is not unusual for a mature tree on a residential property to have an asset value of $1,000 to $10,000, and to confer annual benefits of $500 or more.
Generally speaking, the larger the tree and the greater its leaf surface area, the greater its annual benefit and the higher its asset value. We may choose to cut down a mature tree and "replace" it with a sapling, but when we do so, we are actually destroying a productive asset and replacing it with one that will not achieve equivalent value for many years to come.
How Tree Valuation Can Help Us Manage Our Urban Forest
Although the City of Claremont has a tree inventory system that calculates the value of trees, data from that system rarely enters into our public decision making processes. Doing so could help us to make better decisions about the care and management of our urban forest. For example:
- Our Sustainable City Plan urges us to "expand our urban forest." Using the asset values from our tree inventory as an indicator could help us to know whether we are achieving that objective.
- What would be the effect of a major blight on a species of street tree? Forecasts based on data in our tree inventory could enable us to plan for such an eventuality.
- Tree inventory data could help us set appropriate penalties for people who damage city trees or remove them without authorization.n When residents or private developers request the removal of city trees, data from our tree inventory could provide an objective assessment of the cost to the community of doing so.
- What would be the net costs and benefits to our local environment and community of the proposed removal of city trees to accommodate hardscape repair or private development? Data from our tree inventory software could make it easier to find out.
In fact, all of our tree policies would be clearer and easier to understand if they were tied to the value and benefits of trees.