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Comment by soVeryTired | Hacker News Reader

I'm not sure I understand what it means to measure the "economic value of a tree". Yes, trees provide shade and reduce pollution, but does that really mean one can meaningfully attach a dollar value to a tree?

There are two statements that I think are meaningful: "this tree costs $X to plant and maintain", and "This tree provides benefits that would otherwise cost $X". But if you want to make the latter statement, are you really sure you've captured all the benefits? Including aesthetic ones? Because I'm not really convinced that's possible.

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Urban vegetation:

1. Has high reflectance in the infrared, so they reflect sunlight back to the sky before it is converted to heat. Built surfaces would absorb this radiation and heat up.

2. Reduce heat also by evaporating water.

3. Reduce ground level heat by providing shadow.

4. Remove pollution from air, such as sulfur oxide (SO2), nitrogen oxides (NOx), ozone (O3) and fine particles.

But yes, converting these to money is very indirect and involves a lot estimation.

Urban trees in Israel made the news last week. They were having a huge affect on heat and fine particles due to an urban forest fire.

Next time, try ice plant and jade plant, or just go with concrete.

Whats the contribution of 1. to climate change? Insignificant?

The contribution of trees and albedo in general to climate change is huge. But I doubt that urban trees, specifically, contribute a significant effect. They do greatly contribute to avoiding the also-problematic urban heat-island effect, though.

It is tough to capture complete benefits and express it in a dollar amount, especially because it is already tough enough to measure the economic value of products that haven't yet competed in the marketplace.

The US Forest Service created algorithms to calculate ecological value based on rainwater each tree retains, the electricity conserved, and reduction of air pollution - that calculation just happens to be expressed in dollars. How they make that transition from ecological value to economic value is a mystery to me, but it is just something to keep in mind as you look over this. It is moreso a measure of ecological impact, not economic (though, of course, they are connected).

Natural Resource Economics is a whole field largely devoted to determining the market value of natural resources (trees, rivers, clean air, all sorts of stuff). It's messy work and difficult for reasons that others have pointed out. But it's certainly a real thing, and incredibly useful for policy-making, where being able to speak in dollar-amounts is crucial.

I take economic value to mean tradable/purchasable by another party. I'm basing that definition on the generation and sale of carbon credits in voluntary and regulatory carbon markets and the value power supply companies place on planting trees that reduce power usage (demand side management) like http://www.swenergy.org/Data/Sites/1/media/documents/news/AP...

> I take economic value to mean tradable/purchasable by another party.

Improving public health and reducing e.g. lung cancer can have value for the national economy, even if individual people do not perceive tradable value in things like buying a home on a street with less polluted air, or quitting smoking.

I guess I'm trying to differentiate hard values from soft. Hard values typically show a more direct path between the product and the action making that product. Like carbon markets that directly influence the planting of trees. There's a chain of custody between those two items that we can (read: should be able to) track.

Every value is a soft value. Everything has some usefulness, and we guess at the level of usefulness. You might think that something like an auction is good for defining hard value, but the winners curse [1] shows auctions are just good at finding people with the biggest error in their estimation. A food is another nice example. Might not be interested at all right now, but wait 24 hours without eating, and i'll be all over that meal.

Value is a slippery concept, and i think i'm willing to go out on a limb and say all value is subjective.

[1] https://en.wikipedia.org/wiki/Winner's_curse

FTA: All these are formulated according to figures from U.S. Forest Service that estimate the total ecological benefits a tree gives in dollars. In the case of the tree in the image below, this one has a benefit for its population that amounts to slightly more than $500 USD each year.

You can't expect to get in-depth, exhaustive explanations of complex concepts in a short article, but you should looks the primary sources cited therein and critique those if you feel they fall short.

Look at real estate prices.

There was an article I read not too long ago that showed the areas in NYC with more trees and greenery also command higher rents.

Also on a completely anecdotal level I feel more "at ease" and less anxious when I'm in parts of cities that have a lot of greenery, especially compared to areas that are barren and nearly all concrete/brick/whatever.

I imagine I can't be the only one who feels that way.

There was an article I read not too long ago that showed the areas in NYC with more trees and greenery also command higher rents.

That can just be correlation though, the affluence might make it easier to keep trees or be an indicator of larger setbacks or whatever.

It does fit with the other research that just seeing trees makes people subconsciously feel better.

If the affluent find it easier to keep trees that must be because they exert power to do so, which implies they want them for some reason. Same reasons they would pay more to be around them in the first place? The affluent would find it much easier to get rid of trees, even if protected by regulation, and the land value the trees take up is worth more.

I think the causation implied by this correlation is implied pretty strongly.

As you point out, it's usually fairly straightforward to calculate the costs attached to a given tree.

When you say you're not convinced that it's possible to be really sure you've captured all of the benefits, do you mean captured their exact value? Or a hard upper bound of such? Or a soft upper bound with a given confidence interval? Or even just enumerated all of the benefits?

I think calculating an upper bound with confidence interval for the value of a tree in a city would be a really interesting exercise. To do it properly you'd have to account for everything from tangible benefits (shade, reduced CO2) to vague generalities such as residents who "feel happier living in a city with lots of trees". I think it'd be possible, but definitely not trivial.

How would you evaluate your estimate? I can't think of any objective way of testing whether you have the 'right' answer.

Short of using two similar cities and varying the tree density in one while making the other a control group, I'm not really sure. I was thinking of the number more as a way to assign value than discover it. Good question though!

In LA the economic value of a tree is overall negative - as the fast growing trees planted long ago have become too large and destroyed miles of sidewalks

In what way is that sufficient to suggest that the net value is negative?

I'm estimating. There is 11,000 miles of sidewalks to fix. plus the problem is kicked down the road to homeowners.

http://www.nbclosangeles.com/news/local/LA-Expected-to-OK-Pl...

"$1.4 billion plan to repair a backlog of broken sidewalks that will allow the city to turn over the responsibility of future upkeep to property owners. City officials plan to spend the funds, which will average at least $30 million a year over the next three decades"

It's important to put these numbers into perspective instead of just using the shock value of "billion" — LA County has a $28 billion annual budget.

0.1% of LA county's budget next year will be repairing damage from trees.

I'm not going to argue whether that's a large or a small amount. Just want to put the $1.4B number into perspective.

"Has some negative effects" != "is overall negative"

Surveys, the same way National Parks are valued at $92bn

http://time.com/money/4389722/national-parks-economic-value/

"I'm not sure I understand what it means to measure the 'economic value of a tree'."

As ^green infrastructure^.

Trees->flowers->insects->pollination. Lack of pollinators can be compensated by more trees. This is but one example ~ https://www.epa.gov/green-infrastructure/what-green-infrastr...

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