What use is a tree when it dies? You may think not much, however dead wood is a vital component of the woodland ecosystem, with many functions including providing food and breeding areas for a wide variety of organisms, nutrient cycling, soil formation and hydrological cycling. In fact, the biodiversity of a woodland is increased massively due to the presence of plenty of dead wood.
A dead sycamore stump showing holes made by the wood boring beetle Anobium punctatum.
So having dead wood around is great, but the type is also important, with different organisms utilising wood of different tree species, different sizes, differing stages of decay and both standing and fallen dead wood.
A well rotten branch supporting a good growth of moss.
Species that feed directly on dead and decaying wood are known as saprophytes. This includes many species of fungus and insects such as beetles. Some species of fungus are specific to tree species, such as the birch polypore, otherwise known as Piptoporus betulinus, whereas others target a variety of tree species, but may cause decay in different ways – known as white rot and brown rot depending on what part of the wood they decay.
A standing dead birch stem supporting the birch polypore as well as other fungi including the hoof fungus.
Many saproxylic fungi also provide food for other species, notably species such as fungus gnats, (Family Mycetophilidae) and beetles such as Platyrhinus resinosus, which feeds on King Alfred’s Cakes (Daldinia concentrica), a common fungus often found on ash and beech.
Insects too make use of dead wood, with numerous species of beetle feeding on decaying wood as larvae. Such species include many of the longhorn beetles (Family Cerambycidae), such as the spectacular Rutpela maculata and Rhagium mordax and the less colourful, but equally impressive Dorcus parallelipipedus, the lesser stag beetle – brilliant name too!
A fallen birch stem, with beetle exit holes visible at close range.
And let’s not forget the larger organisms that benefit from dead wood – the birds and mammals. Many species make their homes in dead wood or indeed in dead cavities within living trees, which provide excellent nest sites for woodpeckers, other hole nesters such as blue, great, coal, marsh and willow tits and bats such as the noctule. And even piles of dead brash can have their use, making ideal nesting sites for smaller birds like blackbirds, robins and wrens and small mammals such as mice and voles.
A brash pile suitable for breeding birds and small mammals.