The Cost of a Tree? (v2)

How much should it cost to chop down a tree? What is the value of clean air? How do we define that value? What discount factor do we apply? -- Irina Filippova in True cost of natural resources

Many years ago the UK government held a public enquiry regarding building a new airport runway terminal. They tried to do a cost benefit analysis, and included the cost of things like, the historical value of an old church, which would have been demolished. They ran into difficulties though, because subjectively it was easy to equally justify the cost being this or that, which made the final answer about what was the best option quite meaningless. 

I guess there is a real problem when we try to objectify something that isn't objective. Perhaps that's a confusion of quadrants. Plus bear in mind, we're not talking about a fixed resource, like a Picasso painting, of which there is just one artist, never to be repeated. We're talking about living energy in multiple interacting forms.

When an asteroid hit the planet Earth 65 million years ago, as is currently hypothesised, and wiped out virtually all the dominant life forms, and blacked out the skies long enough to kill most plant life, leaving just a few small critters to survive, was that a "cost" to the planet? It could be argued that the dinosaurs were preventing new species from developing. Their extinction gave small mammals a chance, and we are their children. How do we "cost" that? Was it a net loss, or a net gain? 

I'm not saying the matter of "cost" is irrelevant, because naturally, we need air, we need water, we need food, we need medicine. It could also be argued we need books, the internet, culture, art, poetry, and religion, because we need meaning. We know these things have value, and we pay for these things with money, but individuals make their own personal choices about how much they want to spend. 

Also, the natural resources that we use are often also human resources. Millions of people can't just turn up to a river and start using it, as it becomes contaminated and unusable. Millions of people can however, use their brains and organise a system whereby the water is cycled through cleaning systems and distributed carefully to each family. That's really why there are so many people -- we've been learning to make better and better use, organising better systems. 

If there are no people there to buy it, does a tree in the forest have any value? Just take humans out of the picture, and all there is is all there is. Now if humans want to use that tree, can they organise, learn the way forests grow, and create a system whereby the trees can be used and reused and so on?

Life reproduces.

Our problems arise when we can't understand the cycles; when we can't invent new methods; when we can't create energy out of energy. What is the value of empty space? At the moment, nothing. What if zero-point energy was possible? What if in 1000 years we gained that knowledge, then what would be the value of empty space? It would be infinite.

So how do we establish the cost of cutting down a living part of the living system? 

changelog: 

v1 - tried to answer and failed

v2 - leave the question open