Insects, mushrooms, earthworms, and other soil dwellers take organic material and, through digestion, convert it into humus - a key element of fertile soil.
Fallen leaves from Fall and Winter contribute to this, and that is what allows the regeneration and growth in spring.
It is mother nature's recycling process!
Also, did you know the word “humility” comes remotely from the Latin word humus, meaning “earth”?