Dead wood is dead good

There's a saying amongst ecologists and entomologists that 'dead wood is dead good', which refers to the importance to wildlife placed on seemingly decaying and redundant areas of woodlands. Peter Britton looks at that 'ugly' bunch of insects that provide an important role in local habitats far beyond their size.

Saproxylic beetles are insects that depend on dead and decaying wood for at least part of their life cycle and play important ecological roles in our habitats. Together with fungi, they contribute to the breakdown of dead wood and are involved in decomposition processes and the recycling of nutrients in natural ecosystems.

Saproxylic beetles interact with other organisms such as mites, nematodes, bacteria and fungi, assisting in their dispersal across the landscape. They also provide an important food source for birds and mammals, whilst some species are involved in pollination.

In Europe, there are fifty-eight families of beetles (order Coleoptera) with nearly 29,000 species. The exact number of saproxylic species is unknown, but a database of French saproxylic beetles includes 3,041 species. According to expert opinion, there may be closer to 4,000 saproxylic beetle species in Europe. In the UK, the figure is thought to be in the region of 800.

Dead wood is dead good

Dead and decaying wood offers a large variety of microhabitats, and different saproxylic species have evolved to exploit these niches, with certain species having very specific ecological requirements. Some saproxylic beetles require live old trees with cavities for their larval development, whilst others are dependent on trees that have recently died.

Saproxylic beetle richness depends on the quantity and quality of available dead and decaying wood in any environment with trees and woody shrubs, as well as on tree age structure, total number of trees, varying tree density and habitat continuity.

The diversity and numbers of saproxylic beetles can be influenced by the degree of sun-exposure, frequency of habitat disturbance, i.e. forest fires or clear-cutting, hedgerow management, clearance of fallen deadwood from parks, age of tree stands and presence of certain types of wood-decaying fungi, among others.

Threats

The main identified long-term threats are habitat loss in relation to logging and wood harvesting, and the decline of veteran trees throughout the landscape, as well as lack of land management targeted at promotion of recruitment of new generations of trees.

More short-term and localised threats arise from sanitation and removal of old trees due to safety constraints, in places heavily influenced by humans, e.g. a golf course or park. Other threats include agricultural expansion and intensification, urbanisation, fires and climate change.

Much is left to learn about the saproxylic beetles. In comparison with other species groups, and despite all the efforts of generations of entomologists, the biology of many species is still poorly known. Any research on saproxylic beetles enhances our knowledge of the functioning of ecosystems in wooded landscapes.

One of the most valuable attributes of any golf club, woodland area or parkland is the species that are directly or indirectly dependent on dead, old and decaying wood.

Veteran trees provide nutrition, shelter and anchorage to a whole ecosystem of species and the richness of species a tree supports generally increases with age.

Dead wood is an ephemeral habitat; it will decompose over time, creating rot holes in the branches and hollow trunks that are used as nesting sites by birds, bats and squirrels. Veteran trees support a huge quantity and diversity of invertebrates that can also act as food for nesting animals.

They are also particularly valuable for non-parasitic plants such as lichens, mosses and liverworts. These groups are particularly rich on old open grown trees because these trees provide nice light surfaces to colonise, but also because these groups have a slow colonisation and succession rate, so it can take decades to develop the rich communities.

These trees are important for fungi that decompose dead wood, fungi that form symbiotic relationships with the tree roots and those that live in the leaves or the bark or even between the living cells of the tree. Fungi feed much of the rest of the species in this ecosystem, either directly with species eating their fruiting bodies or mycelium, and indirectly through softening up the dead wood which enables it to be digested by others.

Each feature on the list of veteran tree features adds to the diversity of micro-habitats that the tree provides, so also the variety of wildlife it accommodates.

The role of fungi

Fungi have developed this role over 290 million years, since they evolved the capability to digest lignin, the building blocks of wood.

The living tissue in a tree trunk or branch is found just under the bark and, from here, the tree grows outwards over the years. This leaves a legacy of dead woody tissue on the interior of the tree. Broken or cut branches, tears and other damage to the tree can let in fungi colonies that will start to decompose this dead heartwood.

Although known as a dead wood habitat, most of the specialised beetles for which this habitat is so important actually eat wood that is decaying rather than just dead. As such, the initial decay caused by fungi in the dead wood of a tree is always the first step to creating this habitat. In this way, fungi are the pioneer species that convert, or 'soften' this initial dead wood into the rich habitat for which it is noted. They create the space and the substrate that enables the richness of other saproxylic communities of species to flourish.

This process of fungi assisted tree hollowing is natural and, contrary to older ideas, not a threat to the tree. It is a natural part of the ageing process and, in some instances, can help extend the life of an ancient tree.

Lichens

The richest tree dwelling (epiphytic) lichens occur in old-growth woodlands with long ecological continuity. Old-growth woodlands include old trees, natural death of trees, standing and lying deadwood (left in situ) and natural regeneration; these are usually associated with sites over 200 years old. Wood pasture and parklands support many of the highest grade sites for lichens, with 33% of Red Data List species associated with grazed woodlands.

Lobaria and Sticta are flagship species for ancient wood pasture in the UK and are included on the European Red List of macrolichens.

An individual veteran tree can support a great diversity of species within its myriad of niches; from acid-barked well-lit twigs, to base-rich shaded trunks, from dry overhangs to rain tracks, and wound marks below points of damage. The highest diversity in wood pasture and parkland will occur where there are a range of tree species and ages and fallen or standing deadwood left in situ.

Although south facing slopes are often favoured, lichens are found in a great range of lit conditions from very exposed to deeply shaded at the base of tree trunks. The variation provides different niches allowing for a number of species to colonise one tree or area.

The scale of a site and opportunities for expansion of lichen communities is vitally important; fragmentation of sites through development impacts directly on species that are not able to disperse spores over distance. Neighbouring riverine, hedgerow and way-side trees are important links in the continuum of diversity.

Saproxylic insects

Saproxylic species are not only specialised to what is now quite a rare habitat but are also only able to disperse over small distances. This makes fragmentation a real threat. These beetles now mainly reside in the isolated refuges that have been able to provide a continuous and plentiful source of dead wood.

Almost one-fifth of Europe's wood beetles are at risk of extinction due to a widespread decline in ancient trees, according to a new report which suggests their demise could have devastating knock-on effects for other species.

18% of saproxylic beetles now exist on a conservation plane between "vulnerable" and "critically endangered". Another 13% of the insects are considered "near threatened" and their disappearance could have a disastrous impact on biodiversity and ecosystems.

What can you do?

The demise of insects, especially bees and butterflies, is well documented, with a 40% decline estimated worldwide.

Sometimes, it seems that 'doing your bit' in your corner of the world will have little effect, but leaving a fallen tree or branch to go through its natural decaying process is one of the simplest things to do - assuming it hasn't fallen across a fairway! Even then, the tree can be moved to a safer place and/or chopped up and converted into log piles and living walls.

Include signage to explain to members and the general public the reasons behind these seemingly disregarded areas. Write about them in your newsletters. The more you inform, the more informed they will be and, given the concerns for the welfare of the planet in general, you are likely to garner the respect of your members ... and the wildlife you are helping!

The good old days!

I remember a time when mum used to hang fly paper from the kitchen ceiling to catch flying insects - especially houseflies and bluebottles - in an effort to stop them infesting the house.

No home, it seemed, could avoid half a dozen or more houseflies dizzily circling the lampshade, whilst bluebottles entered any open window or door - at speed - and proceeded to visit every room in the house like an out of control drone, bashing themselves senseless against any closed window in the process. This would go on for what seemed an eternity until the bluebottle either exited from whence it had come, or dad had been successful in hunting it down with a rolled-up newspaper or a purpose-made plastic fly swat.

Outside in the garden, the buzz of bees could always be heard and butterflies fluttered prettily by, whilst wasps would pester anyone foolish enough to be holding a soft drink, jam sandwich or similar sweet confection, often resulting in much thrashing about and screaming. "Just sit still" would come the not so reassuring advice from parents.

Summertime car journeys would result in hundreds of insects being splattered against windscreens and headlights; so many, at times, that the driver would be required to pull over to remove them using a scraper kept in the boot for just such a purpose. Wipers and screen wash did nothing more than smear them over the glass!

May Bugs (cockchafers) and flying ants would swarm in vast numbers, with the former happy to settle in the back-combed or permed hair of young ladies; their buzzing leading to screams of delirium from the temporary host!

Cabbage white caterpillars would appear in huge numbers on dad's prize vegetables and proceed to munch away at the leaves. No problem for me as I despised cabbage!

Many common garden butterflies, such as red admiral, comma and small tortoiseshell, laid their eggs on stinging nettles, the host plant providing food for the caterpillars. Now, nettles are often grubbed out to make way for more 'attractive' plants.

If all this seems a tad fanciful to younger readers, believe me, it is not. Such was the abundance of insects in the sixties through to the eighties. Such occurrences are very rare these days and most car journeys now are 'fly free', whilst homeowners can open their windows and doors safe in the knowledge that, apart from the occasional six-legged intruder, the same is true.

So, what happened?

Intensive farming, in short. It is too deep a subject to go into in detail, but an ever increasing - and demanding - human race required feeding, so all manner of chemicals were poured onto the land to achieve this, whilst hedgerows and trees were grubbed out to provide the maximum area for growing produce and raising livestock.

Supermarkets too insisted on perfect products. No spots on apples, no blemishes on fruit, uniform vegetables, and a plentiful supply of cheap and tasteless chicken; all requiring considerable 'advances' in land management. Something had to give.

The first real signs of anything being wrong came in the early 1980s when a sharp decline in farmland birds was observed; a trend that has sadly continued. A few years later, and woodland birds also suffered a decline in numbers, although not to the same extent. The decline in wetland and water birds has not been so marked, quite possibly because much of their food source is not affected by chemical use. That said, we may yet see a decline in this sector due to microplastics in the sea.

Whilst insects are at the bottom of the food chain, their importance to all life cannot be overstressed. From general pollination - an essential role in itself - through to being a vital food source for birds and animals, insects demand both our respect and protection.