I recently learned that there's a group dedicated to planting 1000 trees in the city of Trenton, NJ, USA. I'm really glad to see a city working to bring back a little nature!

This is missing out on likely the most important part of trees in urban areas. Shade. They give you a cooler place to stand or walk through.

This just makes me think it’s an aquarium that needs to be cleaned.

Upkeep costs. Oh, wait.

Your just thinking outside the box!

A few reasons: Trees need a lot of space and the space underneath a sidewalk isn't enough for long term life. They can die after like 30 years? This is tree dependent and location dependent.

Tree roots can destroy sidewalks making it harder for people to go over them. (Think people in wheel chairs)

Liability in terms of damage (have you seen trees after a storm?)

I guess it would take a lot of time to accommodate Mars for trees. More than for algae ;)

Less infrastructure erosion from roots? Integration into places like above ground parking spaces? Hell could you imagine integrating them into bridge underpasses or walk ways? Heck make a semi destructible version and use that for crash bollards. Only a level 5 vegan is going to complain if some allege is spilt.

Like I always think that people don’t get one thing about trees in a city. There purpose is is not about co2. The co2 reduction of city trees is neglectable. The reason you need them in a city is temperature regulation, shade, air quality, mood, the local eco system and maybe solidifying unsealed ground. Putting these tanks in a city is laughably inefficient w.r.t. co2 conversion if you compare this to any effort to do this in instustrial capacity ( which is is also still laughably inefficient)

We can have both trees and this ! Let’s replace the stupid ad spots on bus stops with these 😮

While I don't want to spoil the joke (but I will) and I hate techno-optimist solutions that displace actual solutions for our biosphere as much as the next person: supposedly, Belgrade is such a dense concrete hell that trees aren't viable solution (at least in the short term).

There is some rumbling that liquid trees are not the solution to the real problems caused by large-scale deforestation, nor does it reduce erosion or enrich the soil. However, much of this wrath is misplaced as Liquid tree designers say that it was not made as a replacement for trees but was designed to work in areas where growing trees would be non-viable. Initiatives like Trillion Trees are laudable, but there is something to be said for the true utility of this tiny bioreactor. The fact that they can capture useful amounts of carbon dioxide from day one is another benefit for them. Such bioreactors are expected to become widespread in urban areas around the world as the planet battles rising carbon levels in the atmosphere.

Source

Can't they just put the algae in the ocean?