Healthy forests are full of life; from the lush tree canopy all the way down to the forest floor. What may look like a bunch of moss, rotting wood, and dead leaves at first glance is actually a rich and diverse ecosystem. In fact, this often overlooked habitat is one of the most important on Earth. Through endless death and decay, the things that happen on the forest floor help support all life on our planet, but how?
Let’s explore why death is so important in forest ecosystems, and how destruction and decay brings new life to the forest floor.
When we talk about the forest floor, we are talking about the lowest level of the forest ecosystem. It consists of soil, leaf litter, decaying organic matter (like fallen branches and logs), insects, small mammals, and other types of vegetation. Due to the forest canopy high above, the forest floor gets minimal sunlight. This creates dark, cool and moist conditions— perfect for mosses, ferns, insects, and fungi that have evolved unique low-light adaptations to thrive.
The processes that happen down here support all life on Earth. Decomposers like fungi break down organic matter (like fallen branches, leaves and bark), giving back vital nutrients to the soil. These nutrients are then used to grow and sustain more trees, fungi, and plant life. When you consider that more than half the world’s land-based animals, plants and insects—and 1.6 billion people—rely on healthy forests, then the importance of this gigantic recycling center is put into perspective.
The animals and insects that live in this dark and damp world are also very important. Insects like ants break apart leaves and twigs on their hunt for food, and beetles drill holes into the tree bark which makes way for other insects and fungi. Soil organisms (worms, snails, woodlice, etc.) return decaying organic material to the earth through their waste. It’s the endless diversity and abundance of species down here that makes forests teem with life.
Fungi are the forest floor’s main decomposers. Walk around any old growth forest today and the tree trunks will be littered with all kinds of mushrooms. The mushrooms that we see (and eat) are actually the ‘fruit’ of the mycelium network—billions of fine white strands that form the underground part of fungi, kind of like the hidden part of an iceberg. This network spreads through soil and wood, connecting plants together. You can think of it as the forest’s version of a high-speed internet connection.
Fungi feeds on non-living organic matter like wood and fallen leaves. Many fungi form symbiotic relationships with plants, known as mycorrhizae. This is when the mycelium interacts with plant and tree roots, helping them absorb water and nutrients from the soil. In return, the plants provide carbohydrates to the fungus.
This mutualistic relationship benefits both the fungus and the plant/tree. Some fungi, like beech Woodwart or Chicken of the Woods (known as heart rot fungi) enter trees through hollows and cavities, creating brown rot that causes wood to lose its structural integrity and turn powdery over time.
Of all the elements that a forest needs to thrive, deadwood is one of the most important. It’s so important, in fact, that it is considered a ‘keystone structure,’ meaning that it plays a huge role in taking care of ecological processes and supporting species. Species that rely on deadwood are called saproxylic (from the Greek sapros meaning ‘rotten’ and xylon meaning ‘wood.’) All kinds of animals and plants, together with fungi and other microorganisms, can be saproxylic.
Throughout their lives, trees undergo a number of changes, but rarely just fall over and die. They might be battered by storms, attacked by insects, catch fire, struck by lightning, bent by wind, or crashed into by neighbors. Wood decay takes place over tens or hundreds of years, and begins in living, healthy trees. These events create rich new habitats for all kinds of organisms to call home, whether in broken trunks, water pockets, or hollows. In Europe, it’s estimated that 30% of the birds that live in forests use tree hollows to nest. Lift any rotting log from the ground, and you’ll find insects galore!
As trees grow old and weak, various species take shelter, food, and nourishment from different stages of death and decay. This diversity is what makes natural, old growth forests so full of life—and why so many species can rely on deadwood to survive.
Deadwood also has a big impact on river health. Fallen trees create safe areas for fish and other invertebrates to breed, while also providing a natural flood defense by slowing down the river flow. Deadwood also helps keep river water clean, filtering out pollutants and improving its quality.
A tree becomes deadwood when it dies, but during some parts of the year (like late fall and winter) it isn’t always easy to tell the difference between living, healthy wood and decaying deadwood. Here are a few ways to identify deadwood from living trees in forests:
In forest monocultures, there is no deadwood. Trees planted for logging grow so fast that their trunks and branches are too thin and cannot support nesting animals and birds. As a result, they cannot grow a proper canopy, letting lots more light down onto the forest floor and allowing only certain types of mosses to grow. Wood beetles and pests spread quickly, reducing the forest's ability to protect itself against invasive species.
The practice creates ‘green deserts’ where all the trees are the same age and none are left to rot naturally, totally removing the vital diversity the forest floor needs to support a healthy habitat. One 2021 study stated that only 3% of the planet’s surface can be considered untouched wilderness, meaning that all those important, life-supporting processes we have talked about in this article have vanished from many parts of the world.
This is why rewilding and conservation initiatives that focus on planting a diversity of plants, trees, and crops encourage species to return to the green deserts, transforming them into biodiverse habitats. While simply planting more trees might seem like a great solution, it’s the variation of species that makes the difference over time. Other strategies—like killing trees to create more deadwood and letting nature take over—is another solution to our monoculture problem.
Overall, forests need a healthy amount of death and decay to remain strong and biodiverse. The next time you find a fallen log on the ground, take note of all the different species living in and around it—the result may surprise you!
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Woodland Trust: Life in deadwood
Insects in the forest ecosystem
Decomposing fungi
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