This. Trees (especially large ones) are a pain to irrigate properly, might not be drought-resistant, grow very slowly until they reach their full potential at removing CO2, interfere with infrastructure that we humans are used to (piping, electricity, telco), roots break up pavements, branches can be a hazard after storms, fruit might attract rats, …

I’m very much pro trees (despite what I’ve listed in the first paragraph), but I’m sure there are places in cities where you can’t plant trees but could put up algae tanks.

If you understand German (specifically Austrian dialect) you might like this podcast episode about challenges and methods to overcome them in the context of greenery in the city of Graz:

Simple Smart Buildings: Bäume in der Stadt

Webseite der Episode: podcasted3e6b.podigee.io/153-baume-in-der-stadt

Mediendatei: …podigee-cdn.net/1742586-m-9ecab280e580cd07f75c83…

TL;DL of this episode: it’s not as simple as “just plant more trees”.