Planting trees on rooftops?
I recently visited Cira Green, a park in Philadelphia that's located on top of a parking garage, about 100' off the ground. The park features numerous garden beds and native trees. There are a number of challenges that come with planting trees on elevated surfaces including soil volume and mixture, ...
Like the video already outlines... lots of structural issues for having trees there, while planted cascades and similar green-roofs are much simpler and easier to build. I think this is one of the cases where the result does not justify the costs/efforts required.
Probably doesn’t make sense for standard residential buildings but for these tall buildings that are highly engineered, does it really increase the costs by that much? Trees offer a large increase in benefits over other types of vegetation due to the shade and many times greater biomass.
That said, simpler green roofs should also be more widely used in cases where trees are too heavy or expensive. And vines and green walls too. I want to see the concrete jungle become an actual jungle!
Assuming the structure can support the weight, I'm all in favor of green roofs. Though, most buildings are privately owned and therefore are not true replacements for proper public greenspace within a city. I think it's also important not to get distracted from the primary source of land waste within cities: car infrastructure.
Lately I've been thinking about how a city would look if you could take up street and sidewalk, plant trees, and keep just a bike path through the middle. The logistics challenges (maintaining access to buried infrastructure/protecting them from roots, and making sure vehicle-based emergency services like firetrucks and ambulances can get everywhere, handicapped people have options/access everywhere) are keeping me busy but I have a couple ideas for photobashes of solarpunk streets to try out eventually.
