It turns out it's not just the disappearance of rainforest trees — mahogany, teak, Brazil nut — that is cause for concern. In a new paper, "Street Trees — A Misunderstood Common-Pool Resource," Indiana University environmental affairs scholars Burnell C. Fischer and Brian C. Steed note that the tree cover in a number of metropolitan areas — the so-called urban forest of street trees like ficus, sycamores, and dogwoods — has declined dramatically. (According to Trees Atlanta, a nonprofit conservation group, Atlanta has lost 60 percent of its tree cover in the past two decades.)
"The loss of forests in municipal areas has drawn parallels to the loss of rainforests in other parts of the world," write Fischer and Steed, "and has generated increased calls for better management of urban forest resources."
Part of the challenge of better management, say the authors, is the confusion that surrounds street trees and "tree spaces." Many jurisdictions lack even an inventory of the trees they have, which Fischer and Steed say is essential for effective management. And it's often unclear, at least to an adjacent property owner, who owns a street tree and is responsible for its care. These arrangements vary by municipality, with local governments sometimes assuming ownership and care and sometimes "delegating" all or part of those interests and obligations to adjacent homeowners, homeowners' associations, or community organizations.
But according to the researchers, the greatest ambiguity surrounding street trees stems from the common perception that they are a public good - meaning that their benefits can't be limited to certain people, and that the benefit one individual receives from them doesn't diminish anyone else's. Although Fischer and Steed acknowledge that street trees share these characteristics of public goods, they argue that the urban forest should be considered a common-pool resource: one that's broadly available and at risk of deterioration if it is overused.
Competing uses, rather than overuse, pose the greatest threat to street trees, contend the authors. The benefits to specific parties of cutting down trees to facilitate construction, improve visibility of commercial signage, or limit liability from falling limbs frequently win out over the benefits that intact trees provide to all, such as reducing air temperature, protecting watersheds, and absorbing greenhouse gasses.
To prevent the loss or degradation of street trees, Fischer and Steed emphasize two principles as keys to successfully managing a common-pool resource: (1) clearly delineated rights and responsibilities relating to street trees, beginning with an unambiguous definition of "street trees"; and (2) a dependable enforcement process. The researchers don't recommend a particular type of management system - private, municipal, or community-based - over another. Instead, they suggest that the significance of viewing street trees as a common-pool resource comes from the realization that "sound management mechanisms are necessary for the survival of the resource. In the absence of these institutions, tragedy often ensues."