Can you provide any reference/elaboration for your claim that tree survivability is not a problem? It's directly counter to the arguments made in the article. Grasses and shrubs are a lot more hardy than trees, as anybody who's even been on a mountain can attest to.
Your other points are well taken and they are sort of addressed in the article in the form of the infrastructure issues. I think the author also would agree that it's sort of feasible in theory, but extremely expensive and impractical.
But you need a meter of soil, two meters would be better. This is 10-20x as much soil as is currently available on most green roofs (or mountainsides).
There are already pictures in this thread of buildings with trees on top, so... the idea that somehow trees are subject to instant death when lifted off the ground is silly. The conditions are not any harsher than trees living in an asphalt jungle in the city are subjected to every day.
It called my attention that in South Finland there are pine trees which apparently are able to grow with their roots barely covered with soil. Some sit directly on hard rock with all their roots visible. I took two photos of this on 2006:
http://pix.hamoid.com/finland2006/nature_is_a_huge_canvas.jp...http://pix.hamoid.com/finland2006/going_back_to_my_roots.jpg
Those trees survive winter winds at -22F (-30C) with very little sunlight, although sometimes winds knock them down making a vertical wall out of the exposed roots.
You are right, if one sees roots it doesn't mean there aren't other roots.
I think the difference is, South Finland was compressed by 1 km of ice during the last ice age, and the ground is pure granite that is blown up using explosives whenever a new building or road is built.
In those places I talk about, the dirt layer is extremely thin or often nonexistent. The photos I linked don't show that, but many trees are clearly sitting on pure red granite rock with just a little bit of dirt and moss surrounding the roots, in the middle of pale rock.
Yes, and the article directly addresses this: Still, plants in these environments aren’t usually tall and graceful. In other words, not the tall trees we see in architectural drawings.
Though I'm personally very partial to the gnarly mountain trees, too.
> Can you provide any reference/elaboration for your claim that tree survivability is not a problem?
Mountane ecology start a 1500ft at the very lowest (e.g. in Scotland), and a characteristic of them is that they're generally forested. Elevation is not an issue. Wind and exposure mostly mean that no all species will handle it (duh) and you will have the usual loss as not all saplings will survive, but trees do grow, even in windy environments with no groves to buffer them.
Conifers are extremely hardy trees and will grow without issue. Hell, a mere 500ft might be too low and warm for them.
Your other points are well taken and they are sort of addressed in the article in the form of the infrastructure issues. I think the author also would agree that it's sort of feasible in theory, but extremely expensive and impractical.