Toronto completed a similar initiative after Hurricane Hazel in 1954. A number of neighbourhoods in valleys were not rebuilt after devastating flooding, and the city was left with wonderful green space, especially in the Don Valley. For me, it’s a “top 10” biking experience, to cross Toronto by bicycle along the trail system.
As an aside, it took a minute for me to parse the OP as I initially took it to mean some sort of infrastructure resiliency project (buying outhouses vs buying out houses).
MD has some replace-felled-trees law, but it’s kinda crappy cause trees can be planted somewhere else entirely. So a big development can be treeless.