All bark and no bugs : SCIENCE
Tidy forests cleared of rotting wood and dying trees are rapidly losing their wildlife, says Malcolm Smith Fallen trees are home to hordes of wood-boring insects and a plethora of colourful fungi - forest life from the dead
Sunday 26 February 1995
But appearances can be deceptive. The trees here may be thriving, but much of the wildlife they support is heading towards extinction. One of the main reasons is a shortage of rotting wood - along with the "rotters" that decompose it - and an unhealthy human preoccupation with keeping forests ``tidy''.
In Finland, as in every European country, natural forest has become exceedingly rare. Ever since man began managing timber - for house- and ship-building, iron-making, or just for firewood - dead and decaying wood has been taboo. Foresters are obsessed with tidiness and healthy trees; dead branches get in their way, and make their pristine forests less viable.
We have, as a result, become used to a sanitised version of forest. A few dead branches strewn about spark fears that the whole eco-system is about to self-destruct. Fallen branches are invariably removed. Decay in living trees - if they are of commercial value - is cut or treated. Any trees that fall prematurely are cut up and cleared away.
Most disastrously of all, no trees are left to become naturally gnarled and aged, impressive because of their very senescence. They are no longer allowed to shed their huge limbs as they, very slowly, give up their own lives to provide a habitat for other forest creatures.
In natural forest, by comparison, half the timber will be in various stages of decomposition: age-old giants with dead limbs, fallen branches, rotting stumps. Whole trees, enormous with age, will have fallen on the forest floor and become home to a plethora of colourful fungi and hordes of wood-boring insects - forest life from the dead.
Dead wood is a forest's richest wildlife habitat. In Britain, one-fifth of our insects - particularly beetles, flies, spiders and pseudoscorpions (harmless scorpion lookalikes) - are utterly dependent for their survival on dead timber. Wasp-mimicking flies, longhorn beetles, click beetles, hornets, robber flies, weevils and many others thrive on it. So, too, does an array of fungi. The white, fan-shaped funnels of angel's wings grow on rotting conifers; the pale, yellow-brown gregarious elf cap on oak stumps; and the cream, aptly-named cauliflower fungus - an edible one - on the base of pines. There are hundreds more.
This army of rotters slowly decomposes the dead timber, returning nutrients to the soil. Expensive fertilisers add what rotters would do for free, processing up to 10 tonnes of dead wood per hectare each year. Forest insects also provide a rich food supply for a third of Britain's woodland bird species, including woodpeckers, warblers and titmice.
"Around 40 per cent of these creatures are threatened with extinction Europe-wide," says Dr Martin Speight, an expert on the insects that thrive on dead wood who works for Ireland's wildlife service. "Some populations are now up to 1,000 miles apart because so few forests have any significant quantity of dead timber left." Ancient forests have a larger number of threatened species than any other habitat. Most are rotters. Originally, every forest would have had a plethora of them.
In southern England, the great storm of 1987 provided a rare opportunity to enrich a substantial number of woods. Conservationists - and many foresters - are convinced it was an opportunity missed. Instead of being left to rot, vast amounts of fallen timber were extracted. What couldn't be sold, often at knock-down prices because the market was satiated, was burnt. More damage was done to many a Sussex and Kent woodland by timber extraction than was caused by the storm itself, according to the Council for the Protection of Rural England and conservationists at the wildlife trusts of those counties worst affected.
Why were foresters so determined to see dead timber off their land? Much of their paranoia stems from a fear that the fungi and insects that rot dead wood might do the same to healthy trees. A few can - spruce bark beetle and the infamous Dutch elm disease (caused by a fungus spread by bark beetles), for instance. But the overwhelming majority don't cross the divide from the living to the dead.
"If they were able to attack healthy trees, forests could scarcely exist," argues Dr Speight. A living tree has a battery of defences, both physical and chemical, against being eaten alive. These mechanisms break down in trees only when they become very old, decayed and damaged, usually by storms.
The foresters' misapprehensions aren't just ridding Europe of dead wood, insects and fungi. Some forest birds are in decline too. The white-backed woodpecker is one - a beautiful, red-capped, black and white variety that depends on old and decaying trees, preferably aspen and birch. It feeds mainly on fallen trunks and rotten stumps, probing deep inside for insects Once widespread in Scandinavia, the woodpecker is now confined to southern Norway and Sweden and parts of Finland. It is no longer common anywhere.
Dead or dying trees that remain upright provide nesting places for woodland owls and forest bats. Greater Horseshoe Bats, in decline across central and southern Europe - including southern Britain - have been deprived of many of their natural forest roosts. Most have taken to buildings as a poor substitute for tree cavities.
Fallen trees and logs protect saplings, the future woodland canopy, from grazing animals. They provide nooks and crannies for plants such as mosses, liverworts and ferns to thrive in.
With so many species at risk, what can be done about Europe's over-sanitised forests? In a study for the Council of Europe, Dr Speight has listed forests which are likely to be of international importance in terms of supporting wood-rotting insects. In many cases, the term "forest" is a misnomer; some are just a few tens of hectares in area. Sweden, with 31, has the largest number surviving. Among the country's huge area of commercially exploited forests, some gems clearly remain.
In Britain only a handful of forests are listed, including the Scots pines - many of them large and old - of Abernethy Forest in Inverness and the aged oaks and beeches of Windsor Great Park (rich in insects, lichen and fungi). Epping Forest and the New Forest are others. Ireland has no sites, reflecting its paucity of woodland generally and the almost complete absence of natural forest with old trees and dead wood.
Now that the prime forest sites have been identified, what should foresters and conservationists be doing? The first priority, says Dr Speight, should be their protection - by which he means no commercial exploitation. Stan- ding trees should be left to fall naturally; fallen timber on the ground should be allowed to rot where it lies, all of which goes against the grain for many a traditional forester.
These measures alone may not be enough. If dead wood is particularly scarce, "protection" will have to be more proactive. It may even be acceptable to kill some medium-aged trees to fill the gap until older trees become senescent naturally. In some Swedish forests where this is practised, white-backed woodpeckers have returned. Transferring dead timber, from forests with a rich array of rotters to forests where they are scarce, has also been suggested.
In Finland, where two-thirds of the country is tree-covered, only 460,000 hectares of forest out of 20 million are protected in national parks and reserves. That is little over 2 per cent of the total; the rest is commercially exploited. A very much smaller area contains old trees and a natural supply of dead wood. Attitudes are changing, however. The Finnish Forest and Park Service is surveying the country's forests to locate the most natural ones, so that more of them can be considered for protection.
Just over Finland's eastern border, however, Finnish companies are logging the extensive spruce forests of Karelia - once part of Finland but annexed in the Second World War by the Soviet Union. Russia needs the money. The loggers will take the largest, oldest trees, depriving these magnificent forests, too, of their insects. Ironically, some of Sibelius's grandest and most majestic music - evocative of towering, sturdy forest trees - takes its name from here: the Karelia Suite. !
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