This type of energy derives from living things, such as plants, animals, and humans. It combines natural elements like earth, air, light, and water, following a cyclical process involving birth, growth, maturity, death, and decay. Only sustainable practices, such as returning organic residues to the soil, can preserve biological energy. Renewability, reliance on natural cycles, and the need for careful management to sustain its balance characterize biological energy. In the context of The Unsettling of America, it represents the traditional, cyclical approach to energy use that is in harmony with natural systems. This concept emphasizes the interconnectedness of life and agriculture, showing how preserving and returning energy is crucial to maintaining ecological balance.

The maximum population or level of activity that an environment can sustain without experiencing long-term degradation is its carrying capacity. In agriculture, it involves the number of crops, animals, or people that a piece of land can support while maintaining its productivity and ecological health. Natural limitations, such as soil fertility, water availability, and the balance of nutrients, define carrying capacity.

Berry uses the concept to highlight the ecological limits that industrial agriculture frequently ignores. In contrast to biological energy, industrial energy pushes beyond natural boundaries by using synthetic fertilizers, monocultures, and mechanization, thereby depleting the land’s resources and disrupting its natural resilience.