As summer turns to fall, and the days get colder, the branches overhead become bare as their leaves fall to the forest floor. The seedlings which were previously sprouting out of the earth and developing vibrant green leaves of their own are now drowned out below the yellow and orange leaves of their taller kin. Now, every step in the forest comes with a loud crunch as the oak, maple, ash, and hickory leaves pile up. Each movement within the forest, no matter how small, is now accompanied and exaggerated by the shuffling of the litter. Chipmunks and squirrels alike create sounds worthy of an animal magnitudes larger. It’s now impossible for even the slightest of breezes to pass unnoticed. But while the small mammals of this deciduous forest must now forage with added caution, earthworms, fungi, and other fauna in the soil are now surrounded by a bounty of potential nutrients. And so the process of leaf decomposition, wherein the nutrients will be cycled back into the soil, where they will once again have the chance to be absorbed by a number of plant species, kicks into gear once again.
At first it may seem a slow process; the fungi and bacteria start to colonize each leaf which is suitable and within their reach. Earthworms, millipedes, and mites start to chip away at the fallen leaves before their outer layers become too hard for the worth of their efforts. With each cell broken down, or each bite of a leaf, no matter how small, a transformation occurs. The previously inaccessible building blocks of the plant matter become fuel for these organisms, and a portion of the fuel is spilled out back onto the forest floor.
The organisms which rely on the leaf litter directly for sustenance are not the only creatures sparked to activity by the falling of the leaves. The oncoming wave of nutrients brings a new life to the forest floor. Slugs and snails, sowbugs, spiders, centipedes, and springtails, are just some of the organisms which call the leaf litter their home; and they each have their own reason for doing so. Sowbugs, for example are attracted to the decaying matter and the moisture that lingers under the litter. The leaf-litter dwelling spiders prey upon the other creatures which have come to the leaf litter with a more innocuous intent.
The microorganisms which decompose the leaf litter have become used to their favorite leaves. After many lifetimes spent underneath the same tree species, they become specialized at decomposing those trees’ leaves. This represents a small, but noticeable, step towards potentially greater changes in species of tiny organisms.