The Value of Trees
By Neil Norton

I struggle with using monetary value to describe trees since in my heart a poem does a better job. Yet Urban Forests around the world are faced with an enemy larger than dutch elm disease, fire, or the asian long horned beetle- it is commercial and residential development.

The Urban Forest faces a loosing battle to the bulldozer when it is defended with a poem. To defend the trees within our urban areas we have to spell out their value in the language of the developer and our civic leaders-cash. I am not being critical of the so-called "free market" that allows competition to give us the most inexpensive housing and provide a living for a segment of our population. My only wish is to make the playing field more level, after all, saying "save the trees" quickly is dismissed in a planning commission meeting when up against private property rights and the seemingly unquestioned principal of making money off of land. The costs of such development should be more carefully scrutinized before a 10acre track is cleared of trees. I want to compare dollars to dollars. So what is our urban forest worth?

The national urban forest (Lower 48 in United States) has a compensatory value of more than 2 trillion dollars according to USDA researcher David Nowak (Compensatory Value of Urban Trees in the United States, Journal of Arboriculture 28 (4): July 2002). His research team counted more than 3.8 billion trees with an average compensatory value of approximately $630 for each tree. Compensatory value was calculated based on tree trunk area, species, condition, and location. Average replacement cost and transplantable size were obtained from the International Society of Arboriculture. While somewhat impractical, it gives an estimate of the value of our urban forest, much like one would value the assets of a corporation or factory concern (which as we saw with Enron also has limitations). In the case of Atlanta, the compensatory replacement value of the Urban Forest was calculated to be 3.7 billion dollars (ibid).

Interestingly, the compensatory value of the urban forest really only scratches the surface when considering its value. In 1994 it was estimated by researches that in Atlanta alone, the Urban Forest removed 1,196 metric tons of air pollution at an estimated value to society of $6.5 million (The Effects of Urban Trees on Air Quality, David J. Nowak, USDA Forest Service, Syracuse, NY). Like a company, an Urban Forest also creates value, and like a company these earnings should be considered when calculating its value. The functions an Urban Forest performs include pollution removal and temperature modification, in addition to non-tangibles like aesthetics, social and community value, and wildlife value. In fairness, trees can have negative functional value like a hazard tree striking a building. This would be analogous to losses that a corporation might impose, like pollution. What value society will place on these tree functions is unclear at this point but their values need to quantified and understood.

Maximizing net functional benefit of the urban forest will lead to the greatest value to society. The "free market" is great at calculating the initial costs of a development but often lacks consideration of the not so obvious costs and social costs. Based on much of the research being conducted as to the value of the Urban Forest, we are not far away from battling the removal of our urban forest with not a poem or chaining ourselves to a tree but with dollar value. Now it is up to us, the citizens, to use this language to make our civic leaders more aware.