An article in a recent issue of Ecological Economics (Vol. 95 , pp.1-10) presents results from a detailed analysis of the net cost per tonne of carbon (tC) abated from planting trees in the five boroughs of New York City.
Based on GIS data down to 50 feet square cells (4.645 m2), and even finer tree canopy data, the study identifies 183,000 public locations where a tree could be planted. Distinguishing four species of trees, the study takes into account a tree’s survival probability, its lifespan, loss from pruning and removal, distance from the nearest building, location relative to the building, and the building’s age, number of floors and percent residential use, and then calculates net abatement. Putting that against the cost of planting, pruning and removal, the study arrives at a cost effectiveness ratio ($/tC). The simulation model is run over 50- and 100-year horizons.
The resulting cost effectiveness ranges, in the 100-year run, from $3,615/tC for a London Plane to $8,410/tC for a Callary Pear, and, for a London Plane, from $2,755/tC in Queens to $4,938/tC in Manhattan.
By rank-ordering the locations it arrives at a marginal cost curve ($/tC for increasing tC/year) for each of the species that can help decide where to put one’s effort for maximal effect.
These costs are astronomical compared to afforestation in rural areas. One meta-study of 55 studies found the average cost of sequestering carbon through rural forestry programs (taking into account the opportunity cost of land) to range between $117 and $1,407/tC. While street trees abate more carbon, the higher cost of planting and maintaining street trees makes street trees less cost-effective. Planting through volunteer effort would lower the cost.
The study notes that trees offer other services as well, including reducing air and water pollution, increasing aesthetics, increasing property values and mitigating the heat-island effect. The sole aim of the paper was to estimate the carbon offset benefits of street trees.
2014-01-03 – ED