THE TREE MAY BE DEAD BUT ITS WOOD STILL SUPPORTS LIFE
“Dead wood provides one of the two or three greatest resources for animal species in a natural forest ecosystem,” says Charles Elton in ‘The Pattern of Animal Communities’. Although it is quite often removed in an effort to keep things tidy and make space for living trees, dead wood is actually a vital element in woodland ecosystems. 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. Incredibly, forests worldwide produce and decompose 150 billion tonnes of wood every year! This article is adapted from an article by the Woodland Trust that can be found on their website (www.woodlandtrust.co.uk).
DIFFERENT TYPES OF DEADWOOD
Fallen deadwood: 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.
Standing deadwood: 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.
Decaying stumps and roots: A considerable amount of wood is found beneath the ground in the large, woody roots that anchor trees in soil.
Rotting heartwood: 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.
WHY IS DEAD WOOD SO IMPORTANT?
“Dead trees are the biological capital of the forest, and removing wood debris and snags can interrupt the energy and nutrient cycles. We must balance thinning areas for safety and human use, and leaving these standing trees and fallen logs for the important role they play, even in their death.” [Leave No Trace, lnt.org]
Nutrient recycling: 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. Not only is it enriching the soil and increasing its stability, but it also plays a role in carbon storage.
Biodiversity support: “If fallen timber and slightly decayed trees are removed the whole system is gravely impoverished of perhaps more than a fifth of its fauna,” says Charles Elton. 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 (see next point) as well as nesting, shelter and larval development. It may come as no surprise that beetles, ants, honey bees, and wasps frequently use hollow logs and decayed trees to build their nests but did you know that 45% of all bird species depend on dead trees for some important part of their life cycle?
Food Source: It is said that there is more life in a dead tree than a living one –mature trees are made up of mostly dead cells whereas dead wood is alive with life – primarily fungi and nitrogen-fixing bacteria, which are both crucial to the health of the forest. Mushrooms are food for insects, birds, mice, squirrel, and deer. During critical winter periods, highly nutritious mushrooms can compensate for nutrient deficiencies in deer’s native forage (Turkey tail on dead wood pictured below).
While decaying wood plays a crucial role in woodland ecosystems for all wildlife, there are several groups of species that have a particularly close relationship with it.
Fungi: Fungi are the principal agents of decay in wood, breaking it down via secretion of enzymes. Some species can feed on both living and dead wood, whereas others specialise in the breakdown of dead wood only from a particular type of tree, sometimes even at a particular stage of its decomposition.
Mosses: Mosses are ecologically important as they are one of the first colonisers of bare ground and exposed surfaces. They absorb huge quantities of water, helping to soak up rainfall and create a humid environment. They also act as an important home for other creatures – these are mainly invertebrates such as woodlice and slugs. Birds will tug moss up looking to expose these invertebrates and enjoy a tasty meal. Moss is also home to a host of microscopic invertebrates such as rotifers, tardigrades and nematodes.
Saproxylic beetles: Many beetles rely on dead wood for the development of 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.
Insectivorous birds: 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.
Bats: 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.
HOW CAN WE PROTECT DEAD WOOD?
Dead and decaying wood can have negative connotations. When walking through the woods, 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 when deciding whether to retain or remove dead or 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 will have a devastating impact on the visual appearance of our countryside and hedgerows. While the biodiversity impacts are also huge, the resulting increase in dead wood habitat in woodlands could actually benefit many species, provided it is allowed to remain.
If you have dead trees or fallen branches in your garden that are not a safety concern, consider leaving them where they are as a vital support for a multitude of different life forms. They may not conform to our ideas of tidiness but they are pretty neat!