Leave your Dead Leaves on the Ground this Fall
Leaf litter, commonly considered an eyesore, is a surprising microcosm of biodiversity. It serves as a cover for the most species-rich habitat: soil, which hosts more than half of all life on earth. Beneath piles of leaves, twigs, and bark, a variety of creatures flourish, from small reptiles such as salamanders and frogs to invertebrates like snails, earthworms, and spiders.
When invertebrates consume leaf matter, they break it up into smaller pieces. Then, tandem forces of bacteria and fungi decompose these pieces and convert them into valuable nutrients such as nitrogen, calcium, and sulfur that helps feed trees and other plants.
Those natural processes help replenish the soil and contribute to the life cycle as dead plant matter transforms into sustenance for living plants. Although leaf litter can look deceivingly stagnant, a microscopic world of activity teems beneath the foliage.
As a microhabitat, leaf litter is diverse. Structurally, it’s made of plant rubble such as leaves, flowers, bark, seeds, and twigs. Chemically, it contains substances such as cellulose and lignin. A 2023 study suggests leaf litter strengthens ecosystem biodiversity by making soil more fertile and reducing the risk of pathogens left behind by animals.
Leaf litter goes through three stages of decomposition to produce soil. The observable top layer is the litter layer. The second layer, composed of rotting leaves, is the fermenting layer. The last, completely rotted layer is built up of a thick and dark organic matter called humus, a type of soil that provides the ideal environment in which plants grow and thrive.
Think of that soil as an entire ecosystem, says Sue Barton, a plant and soil scientist at the University of Delaware.
“The soil system contains the mineral component, which is the sand, silt, and clay. It also has spaces that are filled with air or water, and then it has organic matter,” she says. “Then a living component, like earthworms and fungi and bacteria. It’s good to refer to soil as a complex system, rather than a single entity.”Not only does leaf litter decomposition help release nutrients into the soil, but it can also store carbon in the ground. Forests sequester this greenhouse gas by capturing carbon dioxide in the atmosphere. Through photosynthesis, carbon transforms into biomass, which eventually dies and becomes leaf litter or deadwood.
Leaf litter is also an important habitat for animals. When the bitter months of winter arrive, dead leaves provide wildlife a place to shelter and hide from the elements. Below the detritus, moths and butterflies cocoons lie nestled, and bumblebees burrow to avoid the cold, hibernating over the winter months.
“Most butterflies and moths overwinter in the landscape either as eggs, caterpillars, chrysalises or adults,” says Barton. “Luna moths, Baltimore checkerspot butterflies, and wooly bear caterpillars tuck themselves into a pile of leaves for protection from cold weather and predators. Red-banded hairstreaks lay their eggs on fallen oak leaves. Swallowtail butterflies disguise their cocoons and chrysalis as dried leaves, blending in with the real leaves.”
What to do with leaf litter
There are several options for saving your leaf litter.
Barton suggests raking the leaves off your lawn and into your landscape beds, because letting the leaf litter cover the lawn doesn’t allow light to penetrate and prevents the lawn from photosynthesizing. To avoid leaves fully covering your lawn, you can use a mulching mower to cut the leaves into small pieces.
Doing this, says Barton, “improves the quality of the soil, so the plants that are growing in that area have more nutrients to take up. They'll have a looser, more open soil with better soil structure. That promotes better root growth, which of course, promotes healthier plants.”
She warns against sending leaf litter to the landfill.
“What you shouldn't do is put them in a plastic bag and send them to a landfill somewhere because you are getting rid of a resource. If you send it off to a landfill, that resource won't be able to be reused in somebody's landscape.”