"Slippery Elm/Ulmus rubra," the sign reads. "This tree has provided benefits to society of $32,480 during its lifetime thus far, or $406/year."
A tree is a public good that we tend to take for granted, so it never occurred to me to try and put a price tag on one before. I was shocked by how valuable the tree apparently is.
I contacted McMaster grounds manager Barb Rabicki to find out more. She said similar signs have been posted on a couple dozen trees around campus. The value is calculated based on a model developed by the United States Department of Agriculture. The model appears to be complex, but Rabicki says it is based on "established annual values for many parameters including stormwater management, oxygen generation, carbon dioxide sequestration, pollutant absorption, property value increases (and) energy related savings." Interestingly, the model doesn't seem to take into account that people may just enjoy seeing trees around for aesthetic reasons.
A tree care/landscaping company, Davey, has a calculator on its website to estimate values of trees based on the USDA model. You can estimate the value of a tree based on its region in the U.S., the type of tree, its circumference and the type of setting it's in.
The signs with tree values seem like a really good "nudge" for people interested in preserving trees and forests, as explicitly telling people a tree's estimated value may help them realize how special the tree is.