New York City’s $122-million trees

The New York City Parks Department’s estimate that a dollar spent on the city’s trees is worth $5.60 back is more amusing than useful.

I mean, I understand why they did this study. As the parks commissioner told the New York Times, “Trees are great for a variety of reasons, but how do you explain that to the Office of Management and Budget?” It’s sort of depressing that the Parks Department owes the Office of Management and Budget an explanation of the greatness of trees, but they’re number-crunchers and doubtless are happiest with you when you give them some.

The Times story goes into considerable detail about how the department did its figuring, and I won’t rehearse it here, but consider this assumption:

Trees in lower-density areas, typically in Queens and on Staten Island, are generally more valuable than those in Manhattan and high-density areas of Brooklyn and the Bronx because they provide the greatest environmental benefits, according to Fiona Watt, chief of forestry and horticulture for the city.

“Trees in front of single-family homes will provide greater shade, and it’s intuitive that a large tree in front of a home seems to resonate more than the same tree in front of a huge apartment building,” she said.

It’s not intuitive at all, and therein lies the problem. A large tree in front of a huge apartment building brings pleasure to many more people than the relatively small number who get to see a big tree in a low-density neighbourhood. Ten thousand people a day might walk under a tree on a busy street, enjoying a moment’s cool shade in the summer. In a neighbourhood of low-enough density some days, the shade of a tree might never fall upon the sidewalk when somebody’s walking on it. This does not appear to be taken into account in the Parks Department’s efforts.

I’m not saying I’m necessarily right, but that neither is the Parks Department. The result is an unreliable estimate, the kind of thing you always end up with when you try to put a value on government services. We know what we’re paying, but what we get back is always a slippery guesstimate.

The best police department, for instance, is one that never solves any crimes because there aren’t any to solve. To put a value on a crimeless society, we have to guess how many crimes there’d be if there were no cops, and that’s a fool’s game, and we haven’t even gotten to estimating the economic damage of those crimes. What’s 10 feet of road worth? A safe crosswalk? A library? The economics are so topsy-turvy, so necessarily based on unprovable assumptions, that you can’t tell.

This is one of the foundations of the argument for having governments do as little as possible — the sheer impossibility of proving whether we’re getting value for money. In the case of streetside trees, I wonder whether we’d be best off leaving them to be the responsibility of the owners of adjacent buildings, who get the direct benefits of the shade and increased neighbourhood appeal, and therefore have the most direct incentive to maintain them. Not likely to happen, of course, but there are plenty of big, beautiful trees on private property the world over.


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