It may not look like much, but fallen branches, rotting stumps and dead trees are the lifeblood of any woodland. Decaying wood recycles nutrients back into the soil, provides food and nurseries for rare animals, and hosts spectacular collections of fungi.
Forests worldwide produce and decompose 150 billion tonnes of wood every year.
Wood decomposition is one of a woodland's essential recycling processes and a natural part of every tree's lifecycle. Dead and decaying wood also provides a nutrient-rich habitat for fungi, a nursery for beetle larvae and a larder for insectivorous birds and other animals.
Deadwood comes in many forms, all of which has its part to play in woodland ecosystems.
Naturally fallen branches, bark and toppled trunks, as well as felled wood, hold a reservoir of nutrients which are gradually released into the woodland floor as they decompose. Once they're unlocked, these same nutrients can be reused by living trees and other plants for new growth.
The rarest kind of deadwood is that of dead trees which still stand. Dead trees can be vulnerable to high winds and the tendency for human caretakers to 'keep things tidy', but those allowed to remain in place offer incredibly valuable habitat for wildlife that can live nowhere else. Living trees may also retain large sections of deadwood.
A considerable amount of wood is found beneath the ground in the large, woody roots that anchor trees in soil.
A natural part of the lifecycle of veteran and ancient trees is the hollowing of their trunks, caused as older heartwood begins to decay at their centre. Depending on the species, a tree can live for hundreds of years while actively decaying in parts, with living wood continuing to support the tree towards the outside of its trunk.
It's thought around 30% of Europe's forest-dwelling birds nest or roost in tree cavities.
If wood did not decay, our woodland ecosystems would soon run out of nutrients, so wood decomposition is an essential recycling process. Vital nutrients are released that can be used again by trees for growth – maintaining a healthy ecosystem.
The diversity of species in decaying wood is incredibly high. Part of the explanation might lie in the many kinds of microhabitats it creates. The myriad combinations of decay type, extent and location in different tree species, contexts and climates, are almost innumerable. Plants, fungi and animals then make use of these microhabitats for food as well as nesting, shelter and larval development.
Wood is also a vital component of river health. Just as standing, dead and fallen trees in woodland and wood pastures are important for a range of species, the same is true for stream and river channels, their margins and their floodplains. It is vital in supporting different life stages of fish and invertebrates, for slowing the flows to provide natural flood defence, and for improving water quality by filtering pollutants.
While decaying wood plays a crucial role in woodland ecosystems for all wildlife, there are several groups of species that are deadwood specialists.
Credit: Guy Edwardes / naturepl.com
Fungi are the principal agents of decay in wood, breaking it down via secretion of enzymes. Some species are able to feed on both living and dead wood, whereas others specialise in the breakdown of deadwood only from a particular type of tree, sometimes even at a particular stage of its decomposition.
Credit: Mike Read / naturepl.com
Many beetles rely on deadwood for the development of their larvae. These are known as saprolyxic beetles, derived from the Greek sapros meaning ‘rotten’ and xylon meaning ‘wood'. Their grubs often feed on wood softened by fungal decomposition, or on the fungal bodies themselves. By burrowing into wood as they go they are also afforded some protection from predators. In all, around 650 UK beetle species are thought to require deadwood at some point in their lifecycle.
Credit: Sam Hobson / naturepl.com
Where there are beetle larvae there are animals that specialise in winkling them out. A number of woodland birds have evolved the strong beaks, long tongues and behaviours to help them extract invertebrates from deadwood. Woodpeckers in particular also prefer standing deadwood in which to excavate nest holes - and these in turn may be commandeered down the line by bats and other cavity nesting birds.
Credit: David Chapman / Alamy Stock Photo
Several bat species use crevices beneath bark or rot holes in trees for roosting, hibernating and even breeding. Older trees are important roosting sites as they tend to contain more deadwood and damaged areas which offer safe, dry cavities.
Dead and decaying wood can have negative connotations. When walking through a wood, people may see rotting logs or broken branches and think that the woodland is unhealthy or dangerous. A tendency towards 'neatening' habitats, particularly in urban and suburban areas, could mean deadwood is removed for the sake of keeping up appearances. Safety considerations may also lead to the removal of deadwood or declining trees from a woodland or park.
While the risk that dead and dying trees pose to people and property is usually low, woodland managers must weigh up the safety risks against their enormous ecological value.
It is important to consider management options at an early stage in respect of retaining or removing dead and dying trees. In some situations, dead and dying trees may be left with
no action where they represent a relatively low risk to footpath users.
In many areas of the country, ash is one of the most common species of tree. The loss of ash from woods and hedgerows due to ash dieback disease, Hymenocyphus fraxineus, will have a devastating impact on the visual appearance of our countryside. While the biodiversity impacts are also overwhelmingly negative, the resulting increase in deadwood habitat and structural diversity in woodlands could actually benefit some species, provided it is allowed to remain.
There are many sites across Europe with few ancient trees and a large age gap between the existing old trees and their successors. Usually, we have to wait for trees to develop the dead and decaying wood habitat associated with ancient trees and the biodiversity they support. A practice known as veteranisation can help speed up this process.
Veteranisation is a technique whereby younger trees are intentionally ‘damaged’ in a way which may speed up the development of valuable habitats which otherwise would only be found on ancient and other veteran trees. The idea behind it is to try to mimic nature using tools. The techniques should not kill the trees, but instead encourage the decay process to develop at a younger age, thus potentially shortening the development time for habitats usually only found in old trees.
These techniques are never carried out on ancient or other veteran trees as they already contain valuable habitat. Veteranisation is instead a complementary nature-conservation tool, when time is not on our side. It cannot replace veteran trees, but it may help bridge an age gap.
Restoring damaged ancient woodland to its former glory is just one of the ways we protect and create important woodland habitat. We work with landowners to help them manage woodland sensitively and ensure otherwise overlooked features, such as deadwood, are allowed to remain in place.
With your support we can continue and extend this work to bring even more vital habitat into good repair.
Help us restore irreplaceable ancient woodland and bring it back to its former glory.
Donate to our restoration fund
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Rachel Hoskins • 22 Jan 2019
Trees woods and wildlife
A dazzling array of shapes, sizes and colours. Find out about fungi and lichens, from ancient taboos to magic and medicine.
Trees woods and wildlife
Get the lowdown on woodland beetles that rely on trees and the woodland ecosystem, from decaying wood to dead animals.
