Luckily, those urban green spaces have a similar positive effect on our systems as a full forest would.
Separately, I would like to point to a place like Prospect Park in NYC, where one can find themselves in the equivalent of a new growth forest complete with the majority of applicable local flora. There are also botanic gardens, where one can experience a number of different groups of blooms throughout the year. We're capable of having this be part of our urban experience.