What is a tree worth?

Someone wrote to ask me about the valuation of landscape architecture, and I had to admit that I know very little about the process of assigning value to designed landscapes and elements.

But I do know that there is a fairly well established process for estimating the value of existing trees in the landscape, either as a fixed value to the owner (what you you owe them if you killed their tree) or as an annually accruing value (what are the benefits of this tree to the community). Researchers have just conducted a street tree survey of all 5 boroughs of NYC and found that after you factor in costs for planting and maintenance, the city is benefitting $122 million per year from its street trees. According to the NYTimes, these benefits aren't evenly distributed...

The tree census found that Queens has about 40 percent of the city’s street trees, followed by Brooklyn, with about 25 percent; Staten Island, with about 16 percent; the Bronx, with about 10 percent; and Manhattan, with roughly 8 percent.