The main reason that Aldo Leopold would argue that it is important to protect the Greenbelt is that:
Fragmenting the Greenbelt would put stress on the integrity of threatened ecosystems like the Carolinian forest
Fragmenting the Greenbelt means that some species will be at risk because they don’t have enough continuous living space
Development in the Greenbelt would result in harm to living beings, like tulip trees, which have intrinsic value
Fragmenting the Greenbelt puts animals in danger and separates their living spaces, causing animal suffering