Regenerating land for plant growth requires nutrients derived from animals, such as bone meal or manure.

“even if you were to try and grow plants without animals on land as part of an ecosystem you're going to need at least nutrients that come from animals you might use completely synthetic fertilizers but you could also use animal manure to fertilize your plants any good gardener knows this you're going to use bone meal you're going to use horse manure you're going to use something from animals to put the nutrients back in the land”