The higher the density the less actual Nature needs to be bulldozed over for development. See:
* https://www.youtube.com/watch?v=cO6txCZpbsQ&t=9m28s
Fifteen minutes pedalling in one direction is downtown, fifteen minutes in the other is farm land.
By have more people in a given land area, the remaining land area can be left alone.
Too small living quarters are the problem, not the density.
How would you improve density if you aren't shrinking the space people live in?
Why would the inner city need to be a "concrete hellscape"? You can have decent density without 'concrete hellscapes'. The Oh the Urbanity channel has a video on the (misguided/misinformed) idea that "urban living" = Manhattan / Hong Kong apartment blocks:
* https://www.youtube.com/watch?v=BCmz-fgp24E
Want a front yard, back yard, and garage (attached to a laneway)? Plenty of that was built pre-WW2:
* https://en.wikipedia.org/wiki/Streetcar_suburb
* https://www.youtube.com/watch?v=MWsGBRdK2N0&t=1m8s
Examples (Streetview):
* https://www.google.com/maps/place/125+Hampton+Ave,+Toronto,+...
* https://www.google.com/maps/place/50+Geoffrey+St,+Toronto,+O...
* https://www.google.com/maps/place/70+Jackman+Ave+Toronto,+ON
Even when the "surrounding land" is a 15-20 minute bicycle ride away, or a hoping on a train to smaller a little farther away (or perhaps have train stations at Nature preserves)?
Or perhaps green spaces like New York's Central Park or Toronto's Leslie Street Spit:
* https://tommythompsonpark.ca/about/
* https://www.google.com/search?as_q=Leslie+Street+Spit&as_st=...
regularly interspersed between housing. Toronto used to have a number of rivers/ravines that got filled in for housing:
* https://www.blogto.com/city/2014/02/5_lost_rivers_that_run_u...
People need a green outlook out of their windows, surrounding greenery is linked to various kinds of psychological goodness. Having to commute to an overcrowded, dirty, needle-ridden park or outskirt somewhere isn't an option.
And for wildlife, continuous bands of greenery and routes of migration with only small interruptions (like street crossings) are necessary. Isolated islands are almost useless.