The New York City Park’s Dept. recently completed a two year study to determine the cost v. benefit of urban trees ($5.60 for every dollar spent). So what is the calculus for steel trees? The sculptor Roxy Paine has three steel trees being erected in Madison Square Park. Not much carbon dioxide being removed from the air, but they’re lovely to look at — and that cost benefit-analysis is even more difficult to calculate (click to enlarge photos).