Technical W
oodlands and parklands can be some of the most important invertebrate habitats in the UK, supporting a number of
nationally rare species, the majority of which are associated with dead wood. Although many people may see damaged or dying trees as unsightly, deadwood is vital for the survival for some of our most interesting, brightly coloured, and threatened species in the UK.
Deadwood/saproxylic invertebrates
Saproxylic invertebrates, which rely on deadwood for survival, make up 6% of British invertebrate fauna, and include 700 species of beetle as well as flies, parasitic wasps, moths, bugs, sawflies and spiders. These creatures rely on deadwood in a number of ways; it can provide a home for adults and juveniles, contain the ideal conditions for egg laying and larval development, and offer a food supply in the form of wood, fungi, mould, sap and other saproxylic invertebrates. Importantly, these invertebrates have been described as bioindicators and can be used to assess the overall health of the ecosystem.
Such invertebrate species are essential for the maintenance of overall ecosystem health. Not only do they provide food for birds, mammals and other invertebrates further up the food chain, but they are vital for the natural regeneration of our
‘tidy’ by the removal of dying trees or fallen branches. According to the European Red List for Saproxylic Beetles (2010), nearly 11% of saproxylic beetles are threatened, and 14% are thought to have significantly declining populations.
The role of saproxylic invertebrates in wood decay
Some of the first colonists of dying trees are the bark beetles, which form tunnels at the junction of the bark and underlying wood. Fungi grow on the walls of these tunnels which, in turn, feed the larvae of the bark beetle. Saproxylic predators follow, such as root-eating beetles and clerid ant beetles, which feed on the adult and larval stages of bark beetles. The hard sapwood is invaded in the early stages of decay, and this can only be achieved by those beetles with heavy jaws and good digestive systems. Some longhorn beetle larvae are capable of this, and even larger burrows can be formed by the death watch beetle. These burrows open up the way for other species, such as the larvae of the large robber fly which predate on other larvae and eggs. As the decay progresses, fungi make the wood softer, allowing a greater diversity of species to coexist. Flies, hoverflies, centipedes, millipedes and mites may utilise the wood at this stage, and it may be used as a hibernation site for social wasps, ground beetles and queen bees. In addition, stag beetles, longhorn beetles
Woodlands have many roles to play in a functioning ecosystem, and both living and dead trees are involved in carbon storage, soil nutrient cycling, hydrological processes and the provision of food and shelter for a wide range of flora and fauna. Diverse and properly managed woodlands will ultimately supply the habitat niches required by deadwood invertebrates, as well as maintaining overall ecosystem health.
Management for deadwood
Deadwood can exist in various forms, from entire standing trees with various degrees of rot, to small twigs in the leaf litter. Many saproxylic invertebrates need very specific conditions, therefore size of deadwood, age, species, stage of decay, and whether it is standing or fallen are important factors to consider. When managing a site, variety in the structure of the woodland is vital. In order to protect these communities
of interesting and important invertebrates, woodland needs to be managed primarily in a way that conserves the living trees, as these will become deadwood in due course without the need for human intervention. In woodlands with a high level of management, consider retaining some of the older, larger or damaged trees and allowing them to die naturally rather than removing them. Saplings can be planted so that, in the future, there will be trees
Cardinal Click Beetle ©Hawk Conservancy
woodlands. These species, historically, have survived in natural ‘virgin’ forests, spanning thousands of years, with a continuous supply of ancient trees, falling branches and dead wood. However, saproxylic species have now been identified as the most threatened group of invertebrates in Europe due to the decline in suitable habitat. In the present day, woodlands have been heavily managed by humans, resulting in even-aged forests maintained for timber, with many woodlands kept
Longhorn Beetle ©Trevor Pendleton
and click beetles may also be present, the latter of which can produce a violent ‘click’ to bounce them into the air to avoid predation. Other species may rely on different forms of decay, such as rot holes and sap runs. For example, red rot in trunks and branches of oak trees form an important habitat for the rare heartwood click beetle. Also, the larvae of the hoverfly, Myathropa florae, have long tails, which allow breathing in aquatic conditions such as rot holes which are filled with water.
Stag Beetle ©Angela Horne
reaching maturity on a continuous basis. Choose a mixture of native tree species. Leave deadwood where it is - both fallen and standing, including both twigs and entire trunks. Mature trees with heart rot can still stand safely for hundreds of years without the need for removal. They support a number of rare invertebrates that rely on the unique conditions it provides.
If a branch is rotten, and requires
removal in the interest of public safety, leave it on the ground below the tree. It is
“Saproxylic species have now been identified as the most threatened group of invertebrates in Europe due to the decline in suitable habitat”
APRIL/MAY 2012 PC 119
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