On the forest floor, fallen leaves, pine needles, twigs, branches, and pinecones decay, forming a natural compost heap that regulates the amount of water entering or leaving the underlying soil. This natural fertilizer, called "leaf litter", also serves as a home for numerous animals, plants, and fungi.
Fungi feed on the detritus (dead plant and animal parts), and many animals--like snails and squirrels--feed on the fungi. Earthworms also dine upon the detritus, and they thrive in the rich soil. In turn, the worms provide food for other animals like frogs, lizards, songbirds, and shrews.
Since they eat dead matter, both fungi and worms are referred to as "decomposers". Here, in the leaf litter, decomposers are important because they break down the dead matter into nutrients for the trees to recycle. Without decomposers, forest floors would be buried in thick layers of dead leaves, which would shield small, emergent plants, like saplings and ferns, from the sun and stifle growth.
But decomposers aren't the only organisms that rely on the leaf litter: millions of invertebrates reside here along with thousands of vertebrates. These invertebrates and vertebrates take refuge beneath the decaying leaves and logs, foraging for food and mates. Some, like slugs and salamanders, depend on the leaf litter's moisture to survive during dry, cloudless days. Others, like snakes and wolf spiders, take advantage of the leaf litter's wide range of prey.
This relationship between producers (the trees, who produce the leaves that, eventually, become a part of the leaf litter), decomposers, prey and predators (called "consumers") makes the leaf litter an ecosystem of its own.