How Much Is That Tree Worth?

Here’s something to ponder as you lie beneath a sprawling elm or maple or oak on a lazy August afternoon:

Just how much is that tree worth?

Priceless, you might be thinking at the moment, as your hammock sways gently in the shade. But, of course, that’s nowhere near wonky enough for those seeking to put a price tag on the value of a healthy environment.

A report released last week by the Casey Trees Endowment Fund and the National Park Service attempted to document the economic value of nearly 2 million trees in the District of Columbia. It focuses on the value to our nation’s capital and its residents of air pollution removal, reduced building energy use, and reduced atmospheric carbon, while acknowledging additional benefits of trees, including air temperature reduction and improved water quality -- all of which contribute to improved human health and well-being.

The study used the USDA Urban Forest Effects Model (UFORE) to analyze data collected from 201 one-tenth-acre field plots randomly located within a grid pattern in D.C. and divided into land-use categories. UFORE was designed to use standardized field data from randomly located plots, along with local hourly air pollution and meteorological data, to quantify urban forest structure and numerous urban forest effects for cities around the world.

The resulting value of D.C.'s trees: about $1,875 per tree -- or $3,615,044,000 for the 1,928,000 trees considered in the study. That value was derived from:

air pollution removal (annual): 540 tons ($2,500,000)

carbon storage (total): 523,000 tons ($9,631,000)

carbon sequestration (annual): 16,100 tons ($297,000)

building energy use savings (annual): $2,616,000

structural or compensatory value (total): $3.6 billion

As you can see, some of the value recurs annually (such as carbon sequestration and building energy use savings), while others are calculated over the life of the tree -- a bit of mixing apple and orange trees, as it were. But you get the point.

There are other sources of value not quantified in the D.C. study, such as “hedonic pricing” -- the economic ripple effect on nearby properties and commerce -- and improved human health, including mental health. (A good summary of the economic benefits of urban trees can be found in a 2004 paper by the University of Washington’s Kathleen L. Wolf, available here in PDF.)

But enough wonky pondering. Now, back to that hammock -- and the $3,750 worth of trees holding it up.