This combination of natural history, philosophy, and poetic writing informed the environmental movement. It is perhaps best known for the following quote, which defines Leopold's land ethic: "A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise." In his chapter entitled "Thinking Like a Mountain" Leopold set out the concept of a trophic cascade, pointing out that killing a predator wolf carries serious implications for the rest of the ecosystem.