The science of rot

The five stages of woodland decay

Death and decomposition are vital processes for our natural environment. As gloomy as that may sound, these processes are nature's way of reusing and recycling essential materials.

During autumn, deciduous trees start to prepare for the cooler temperatures and shorter days ahead by reducing the energy they need to survive. They do this by conserving energy and shedding their redundant 'solar cells', leaves.

Discarded by the tree, the leaves make their journey to the ground to join the shady underworld that lives on the woodland floor. The leaf litter layer that blankets a woodland floor is a vital food source for many bacteria, fungi, plants and animals. Each plays a pivotal role in the woodland's carbon and nitrogen cycle.

1. Hung out to dry

Leaf litter © PJ

Some leaves begin to lose moisture while still attached to their parent trees. This occurs during the shedding process. The tree reduces the flow of water and nutrients to the leaves effectively blocking the base of the leaf, an area called the abscission zone.

Once incorporated into the litter layer, the vegetable material dries out through the loss of water and soluble carbon compounds to the atmosphere. Fungi and micro organisms move in to feed, weakening the fibrous supporting structure of the leaf.

2. The detritus division

Stag beetle larvae © Harry Lines

Enter the detritivores. At this stage the rather bulky woodland material heavyweight demolition to break it into smaller pieces. This is carried out by a range of soil inhabitants including ants, slugs, millipedes, woodlice, insect larvae, springtails and earthworms.

The earthworm, one of the most important soil animals, is like a little processing plant breaking down bulky leaf material into the compost-like material called humus. As well as increasing the fertility of the soil, earthworms help with the transportation of soil and air to deeper depths, effectively mixing the soil up.

3. A date with a decomposer

Stinkhorn © Rospix

Next come the primary decomposers, including the foul smelling stinkhorn fungus, which help break the leaf litter down chemically. These families of fungi possess a unique enzyme that is capable of decomposing lignin, the complex chemical structure found in wood. The enzyme is secreted onto the wood's surface degrading the structure into an oozing residue that the fungus can consume through its hyphae.

4. Call for seconds

It's now time for the secondary decomposers, such as springtails, mites and potworms. Springtails act as both detritivores and secondary decomposers with populations of this microscopic animal estimated to be in excess of 100,000 individuals for every cubic meter of soil. Pretty impressive for an animal that most people haven't even heard of.

5. Microbial banquet

Lastly come the microscopic bacteria and fungi. These tiny workers break down the remaining proteins, polypeptides and nucleic acids of the leaf litter into its basic carbon- (carbon dioxide, methane and sugars) and nitrogen- (ammonium, nitrate and nitrite) containing constituents which will be used by growing plants in the spring completing the nutrient cycle.

Next time you visit a woodland make sure you take time to have a rummage in the leaf litter layer to discover its amazing minibeast inhabitants. Keep your eyes peeled for the tiger earthworm, the subterranean slug, the elusive stag beetle and the skilled woodland ants.

We can take a leaf out of nature's book in our own green spaces. Unlike a woodland, our gardens often need additional help in the form of nitrogen fertilisers. Find out how you can benefit from rot in your garden with the NatureUK's guide to 'Finding the beauty in decay'.