Tim De Chant shakes his head:
[T]rees atop buildings have become an architectural crutch, a way to make your building feel sustainable without necessarily being so. And that’s a charitable assessment. Here’s how I really feel—trees on skyscrapers are a distraction from rampant development and deforestation. They’re trees for the rich and no one else. They’re the soma in architecture’s brave new world of “sustainable” development.
In reality, trees on skyscrapers will likely be anything but sustainable. Structures built to support trees need to be over-engineered compared with their abiotic equivalents—trees are heavy, so is dirt (multiply so when wet), and so are watering systems required to keep them alive. If those trees are to have a chance on these windy precipices, their planters had better be deep, which further compounds problems raised in the previous sentence. A skyscraper that’s built to support trees will require more concrete, more steel, more of anything structural. That’s a lot of carbon, not to mention other resources, spent simply hoisting vegetation dozens of stories up, probably more than will ever be recouped in the trees’ lifetimes.