“The duff layer, a few inches above the soil, is one of the most vibrant and biodiverse parts of the forest or garden.”
Barbara Faurot, The magic of duff in the wildlife garden

Decomposing leaves are critical for the health of our yards and our watershed. Each of us can help increase biodiversity, support an amazing community of living creatures and increase ecosystem health simply by leaving the leaves.

Leaves are gifts to trees

“No one rakes the forest.” Diane Ehrich

Fallen leaves are part of a tree’s natural cycle. As they decompose, they return carbon, calcium, magnesium, phosphorus, potassium, nitrogen, trace minerals and other essential nutrients to the soil, feeding trees and other plants. While rock dust is often touted as a miracle soil amendment, leaves are the nutrition powerhouses that contribute many of the essential elements trees and other plants need. The University of Florida found that by using leaves as a soil amendment you can expect good yields of crops such as cucumbers, tomato and greens after 2 to 3 years. As leaves decompose, they also increase the soil’s structural complexity, which increase rainwater retention and increases habitat for diverse organisms.

Healthy soil houses a greater diversity of soil fauna (such as Earthworms, Potworms, Collembola, Mites and Isopods) which means decomposition — the process of organisms consuming plant material — happens more quickly.

Microbes are the main consumers, helped by larger soil organisms whose feces is the main source of food for microbes. Because microbes are too small to see, decomposition rate is often used as an indicator of soil health. Healthy soil also stores more carbon. Burghardt Lab discovered that when leaves are removed, decomposition rates drop by 17% and soil carbon storage by 24%.

Curious as to how soil health improves after you begin leaving the leaves? Try the Tea Bag Index to track decomposition.

Leaves are gifts to streams

Our yards are part of a watershed. In our area, streams and the web of life they support evolved with forests. Leaves are the dominant food resource for small streams, serve s the foundation of complex webs of relationships and supply much of the carbon needed to support a stream throughout the seasons.

Leaves from diverse tree species decay at different paces, supplying food for various organisms throughout their life cycles.

Leaves the leaves for moths and butterflies

Ferlauto & Burghard (2024) documented over 100 species of Lepidoptera from 21 families overwintering in yards. However, removing leaves reduced total insect emergence in spring by 17%. Butterflies and Moths by 45%, Beetles by 24% and Spiders by up to 67%.

Luna Moths are one of many Moth species who pupate in cocoons wrapped in fallen leaves under their host trees (Paper Birch, Black Walnut, Hickory and Sumac). Oaks, according to Douglas Tallamy, support 511 caterpillar species. 94% of the caterpillar species who feed on oak leaves drop to the ground and either dig a hole in the soil or spin a cocoon in the fallen leaves, emerging as adults the following spring.

Dozens of species of Moths and a few Butterflies eat dead leaves. Red-Banded Hairstreak Butterflies lay their eggs on fallen Oak leaves, which become the first food of the caterpillars when they emerge.

Moths, like this Luna Moth that’s being eaten by a Cardinal, are an essential high protein food source for birds, whether in their caterpillar or adult phase.

Leave the leaves for birds

“Fallen leaves are song and motion.”
Nancy Lawson

Many ground-foraging birds — Doves, Eastern Towhees, Turkeys, Thrashers, Thrushes, Flickers, White-Throated Sparrows and more — flip leaves in search of insects, Ants, Moth pupae, Beetles, Worms, Millipedes and seeds. Bluebirds and Flycatchers hunt in the leaf litter, swooping down to capture prey if they sense movement. Blue Jays cache seeds and nuts in soil and cover them with litter, helping regenerate forests. In fall and winter, even Chickadees and Nuthatches forage in the leaf litter. Many birds also use leaf litter for nesting material.

Leave the leaves for bees

If you’re lucky, you’ll spot a Queen Bumble Bee emerging from the leaf litter in the spring. They hibernate in loose soil, pine needle duff and leaf litter.

Leave the leaves for Frogs, Toads and Snakes

Toads and other small amphibians rely on the shelter and moisture provided by fallen leaves and feed on insects sheltering in them. Wood Frogs, Chorus Frogs and Spring Peepers hibernate in fallen leaves. If you have a pond, leaving the leaves provides habitat for invertebrates who in turn are eaten by Frogs, Toads, Salamanders and Birds. In winter, many Frogs hibernate in decomposing vegetation at the bottom of the pond.

Leave the leaves for Fireflies

Fireflies lay their eggs (up to 500) under leaf litter, moss or in the soil. Once they hatch, they spend their larval stage (up to two years) sheltered by decomposing leaves. They feed on other creatures who also live in leaf duff, including snails, worms, slugs and grubs. Without undisturbed, moist leaf duff, fireflies won’t make it to adulthood. 

Leave the leaves for bats

“The next time you find yourself hiking through the woods on a warm winter evening, keep your eyes peeled for a leaf that suddenly flies away – demonstrating a remarkable adaptation to an environment that had been considered out of bounds for winter bats.”
Jessica Hay

Some Eastern Red Bats hibernate by borrowing into leaf duff. During warm winter days, they may emerge to eat insects. Leaf duff protects both the bats and the insects bats rely on (Mormann et al., 2007).

What to do with extra leaves

• Smother a section of your lawn to make a new garden bed like this lawn conversion shared on r/NoLawns by augustinthegarden.
• Use fallen leaves as an alternative to shredded bark mulch to feed trees, plants and soil microorganisms.
• Create a soft landing — a pocket forest or pocket meadow of diverse native plants — around trees or large shrubs to increase structural complexity and trap fallen leaves. You can use stones, stumps or logs to increase habitat and help keep the leaves in place.
• Mulch the leaves into your lawn. Purdue researchers mowed 2 tons of leaves per acre into turf grass annually for five years, increasing microbial activity and health of the lawn. Michigan State researchers found that after a few years of mowing once or twice a week during leaf fall (up to 15cm of leaves at a time), a significant decrease in dandelions and crabgrass.
• Make leaf mold, then use it to start seedlings.

What happens to leaves in spring

Worried that leaves will smother your plants? If you have a naturalized yard, simply leave the leaves be. Come spring, plants will find their way through the leaves. And a month or two later, many of them will have broken down.

Make a leaf duff garden

Leaf duff also serves as a seed bank. Wai-Ora Trust uses duff to gain insight into current and historical species of plant communities. Curious as to which seeds might be in the leaf duff of a healthy ecosystem? Here’s a fun project to try with kids from Kiwi Conservation Club.

References

• Legacy effects of long-term autumn leaf litter removal slow decomposition rates and reduce soil carbon in suburban yards, (Ferlauto, Schmitt & Burghardt, 2024)
• Winter Roosting Ecology of Eastern Red Bats in Southwest Missouri, (Mormann & Robbins, 2007)
• Nesting & overwintering habitat for pollinators & other beneficial insects, Xerces Society
• Revisiting the Fates of Dead Leaves That Fall into Streams, (Marks, 2017)
• Life in the Leaf Litter, American Museum of Natural History
• Removing autumn leaves in suburban yards as a landscaping practice reduces the spring emergence of overwintering insects, (Ferlauto & Burghardt, 2024)