Are Leaves Really “Litter?”
November 18, 2022 | Permalink
State Naturalist Randy Hedgepath gazes at the autumn foliage at Fort Loudon State Historic Park
Nothing signals autumn in our temperate forests like the annual falling of the leaves. One cannot even picture the season without imagining leaves of every color drifting from the treetops and coming to rest on the ground below. For the tree this means an end to the season of photosynthesis and the onset of winter dormancy. For many a Tennessee resident they see their work as only just beginning! A flurry of activity sets about in backyards, parks and businesses, with people busily raking, blowing, bagging, mowing or burning this 'bothersome' detritus.
Yet there is so much more to this leaf cycle than there may appear. Reduce, reuse and recycle are not new concepts to Mother Nature – she has been following these practices for millennia, and she has big plans for all that leaf litter!
There is an entire universe beneath our feet, hiding in plain sight as we wander the forested, leaf-strewn paths. This brown, leafy blanket is a precious sanctum for a myriad of organisms, providing both food and shelter. Let’s take a closer look and see what we can discover…
The first creatures we will observe are nearly microscopic, but if you squint really hard you may see little whitish dots, smaller than the commas in this sentence, springing in all directions as you pull back the moist curtain of dead leaves. These are springtails, one of the many tiny invertebrates that inhabit this layer. It has been estimated that more than 100,000 of them can be found in a single square meter of leaf litter! They, along with a diverse community of fungi, are the decomposers.
Orange Pinwheel fungus (Marasimius siccus) is a common decomposer of leaf litter
You have probably noticed that the leaves that fall do not just sit static and build to great heights year after year – they get consumed! These tiny consumers cycle the nutrients bound up in the leaves back into the ecoysystem, making them available to other organisms. They also form the base of an intricate food web, providing nourishment to predatory invertebrates like firefly larvae, as well as salamanders, hatchling box turtles, tiny snakes, birds and mammals of all shapes and sizes.
Can you find the Carolina Wren that is foraging in the leaf litter?
Leaf litter is a haven of shelter and food for all snake species, including this juvenile Eastern Gartersnake (Thamnophis sirtalis)
While an entire novel could be written about the denizens of this hidden world, we will highlight only a few of them.
Did you know that Tennessee is home to at least 30 different species of fireflies? Like all beetles, they undergo true metamorphosis with 4 distinct developmental stages. They spend the longest part of their lives as a larva, and most of these larvae live in the leaf litter. They are all predatory in this stage, feeding on small invertebrates such as snails. At night they can often be seen emitting a soft glow on the ground, especially next to bodies of water, as they hunt for prey.
Firefly larvae are rather alien-like in appearance. This Pyractomena larva was unconvered while pulling Japanese Honeysuckle.
Another armor-plated Pyractomena firefly larva
When it comes to the enchanting Blue Ghost firefly (Phausis reticulata), the leaf litter is especially crucial, given that the flightless, larviform females spend their entire lives in it and in the soil beneath it!
The Blue Ghost firefly (Phausis reticulata) female is a flightless grub, no larger than a grain of rice
Butterflies & Moths
There are a surprising number of butterflies and moths that depend on leaf litter. For many species, the soft, moist, insulating layer provides a safe place to over-winter as a pupa. They are often very well-disguised as they await spring tucked safely away in their cocoon or chrysalis. Several of the giant silkmoths (Saturniidae) spin their cocoons onto the leaves while they are still attached to the tree, drifting to the forest floor when autumn arrives.
A vacant Polyphemus moth (Antheraea polyphemus) cocoon resting on the leaf litter at Meeman-Shelby Forest State Park
A newly emerged Luna Moth (Actias luna) at Edgar Evins State Park
There are also lepidopterans that over-winter in the larval (caterpillar) and adult stages. Great Spangled Fritillaries delight us with their large orange, black and white spotted wings in early summer, but did you know they spend the winter tucked away under leaf litter while still a caterpillar?
A Great Spangled Fritillary nectaring at Edgar Evins State Park
Wooly Bear caterpillars also over-winter in burrows under leaf litter.
Isabella Tiger Moth (Pyrrharctia isabella) caterpillar, also known as a Woolly Bear
The lovely little Red-Banded Hairstreak is another common butterfly found throughout the state. Its caterpillars take this dependence one step further, by actually feeding on fallen dead oak leaves.
A Red-Banded Hairstreak (Calycopis cecrops) at Edgar Evins State Park
Litter Moths (family Herminiinae) also feed on dead leaves during the larval stage and hide in the leaf litter during the adult stage.
A member of the Litter Moth family, Idia laurentii, at Pogue Creek State Natural Area
Countless other moth species can also be found, often hiding in plain sight, among the dead leaf detritis.
A well-hidden Pyreferra
Look closely to see this Dart Moth!
A Yellow-washed Metarranthis Moth (Metarranthis obfirmaria) at Denny Cove, South Cumberland State Park
Lastly, even our state butterfly, the Zebra Swallowtail, depends on leaf litter for its life cycle. Despite their colorful appearance, they are difficult to find because of their nocturnal feeding habits. During the day they crawl down the Paw Paw trunks and hide in the fallen leaves.
A rare daytime sighting of a Zebra Swallowtail (Protographium marcellus) caterpillar at the author's residence
Bumble Bee Queens
In late fall the annual cycle of the bumble bee colony comes to a close, ending with the fertilized queens (also known as gynes) seeking out a cozy place to spend the winter. She places her burrow under an insulating layer of leaf litter, often utilizing an abandoned rodent nest, to await the arrival of early spring.
A freshly emerged Brown-belted Bumble Bee (Bombus griseocollis) in March
Hatchling Box Turtles
When they first emerge from their eggs, Eastern box turtles measure a mere 1.25 inches across and are quite vulnerable. They spend the first few years of their life feeding on invertebrates and fungi as they travel through the leaf litter layer.
An Eastern Box Turtle (Terrapene carolina) hatchling found by the author and her son at Washmorgan Hollow State Natural Area (and returned safely to where it was found)
Tennessee is home to at least 56 species of salamanders (more than any other state!), and all of them rely on moist environments in which to live. Leaf litter is the perfect refuge for these small amphibians to hide and feed.
Northern Slimy Salamander (Plethodon glutinosus) at Edgar Evins State Park
An Eastern Newt (Notophthalmus viridescens) patrolling the leaf litter at Roan Mountain State Park
Have you ever wondered where frogs go during the colder months? Most aquatic frogs spend the winter partially buried in the mud near oxygen-rich waters. The Wood Frog goes about things a bit differently. It actually allows its body to freeze under a thin covering of leaf litter! It may appear dead to us, and indeed it would be if it weren’t for the glycerol in its blood preventing ice crystals from piercing its tissues. When the thaw returns it will revive and hop away!
A well-camouflaged Wood Frog (Lithobates sylvaticus) at Roan Mountain State Park
Leaf litter provides valuable cover and hunting grounds for all species of frogs and toads.
A tiny Cricket Frog (Acris) ready to spring in the leaf litter at Meeman-Shelby Forest State Park
It isn’t just the fauna that rely on this annual blanket! Leaf litter provides insulation, moisture retention and nutrients to a diversity of native plants, shrubs & trees, including some of our favorite spring wildflowers. This layer is especially important to our spring ephemerals which need extra protection for their perennial organs (i.e. rhizomes, tubers, corms) during the colder months.
Sweet Betsy Trillium (Trillium cuneatum) emerging from the leaf litter at Burgess Falls State Park
Putty Root orchids (Aplectrum hyemale) nestled in the leaf litter at Tims Ford State Park. They will photosynthesize through the winter months.
While shed leaves in most any form have ecological value, not all are created equal. The leaves dropped by most trees break down rather quickly during our wet winters, and are often completely decomposed by the following spring. There is one exception to this rule, however, and that is the oaks.
Oak leaves abound at Fort Loudon State Historic Park. From left to right: Southern Red Oak (Quercus falcata), White Oak (Quercus alba) and Post Oak (Quercus stellata)
Oak leaves are higher in tannins which help resist the effects of decomposition longer. This is important because oak leaf litter persists year-round, providing a safe haven for the many organisms that need it 365 days per year. Research even suggests that oak leaf litter can suppress invasive species such as Japanese stiltgrass (Microstegium vimineum) and Asian jumping worms (Amynthus agrestis).
Oak leaves carpet the ground at Big Hill Pond State Park
If providing food and habitat, cycling nutrients, retaining moisture and combating invasive species weren’t enough, a soft, bouncy layer of leaves also provides a cushion for many species that need a safe place to land from the trees (pupating caterpillars, for instance).
If you want to provide this essential ecological ingredient in your landscaping, but still wish to maintain a lawn, simply rake the leaves to an area that you don’t mind leaving them (they make excellent mulch for flower beds!). Chopping, mowing or burning the leaves unfortunately destroys all of the organisms that take refuge there. Sending them to the landfill doesn’t do them much service either!
Learn more about ways you can contribute to invertebrate conservation at the Xerces Society webpage
With an increasing awareness of more environmentally-sound landscaping, many often ask what it is they can do to help. It really isn't so much about what you can do - it is more about what you do not do! Nature knows how to provide for her own, if we simply allow these natural processes to occur. Inviting this wildness into our lives invites the biodiveristy that the ecoysystem thrives on, and allows us to participate in the rewarding journey of conservation, right in our own backyards.
The next time we head out into the parks to refresh ourselves this Holiday season, let's cherish the magic of this annual cycle - because we know there are countless creatures tucked safely away that are feeling very thankful.