A related article from 2013: http://www.archdaily.com/346374/can-we-please-stop-drawing-t...

"There are plenty of scientific reasons why skyscrapers don’t—and probably won’t—have trees, at least not to the heights which many architects propose. Life sucks up there. For you, for me, for trees, and just about everything else except peregrine falcons. It’s hot, cold, windy, the rain lashes at you, and the snow and sleet pelt you at high velocity."

Edit: it makes me wonder: what about grass. A lot of grass can live up to 2km.