Wednesday 5 September 2007

Touch Wood: The Ecology of a Woodpile

I cannot drive past a firewood truck without scrutinising the load. It is my winter sport. As the surfer seeks the ultimate wave, so I search for the perfect load of wood. In my mind I see it - grey and dry, smooth-grained and barrel shaped, bearded with the pale lichen of its highland home. It splits with the merest caress of the block-splitter, yet resounds with a decent thwack. And it ignites with blushing haste at the first touch of an ember, then burns clean, lean and slow all night. It is the dream of the wood-gatherer. But with the firewood comes an unseen host, a whole ecosystem of which I am ignorant, until a bird shows me.

The grey shrike-thrush, so ignobly named, is one of our most inquisitive birds. And a peerless singer, as its full name Colluricincla harmonica implies. We know it simply as `Jo Witee', after its most frequent call. To `Jo Witee' two tonnes of firewood is a smorgasbord. The unassuming grey bird lands on the wood heap less than a metre away. It works at the wood, probing, hopping, stopping, tilting its head, then jabbing again. Though I call it grey, it is a grey as varied as clouds. On its back is the olive-grey of a coming storm. The beak is stormier still, but the under parts are the off-white of a gentle cumulus. It shows no fear of me, so I return to the mindless work of stacking the wood, accompanied by Jo Witee's rich whipping flute. It is much later, in splitting the stacked wood that I begin to find the bird's quarry.

Taken from their high-altitude home at near enough to freezing, the denizens of the wood find a ten degree winter's day summer-like. Some are triggered into immediate activity, rising to the surface of their cellulose ocean in search of mate or food: ants, moths, beetles, woodlice. Others remain secreted in impossible places. To my astonishment I split a solid log and find a spider web clamped to the freshly-split surface. Where there was surely no gap, a small jumping spider emerges from a web, or a young huntsman from a crack.

Each type of spider has its own personality, its own capacity to evoke fear or favour. But surely even the most hardened arachnophobe couldn't fear the jumping spider family (Salticidae). Small and harmless, one enthusiast describes them as possessing "charm . . . unbounded vitality . . . confident fearlessness". Their family name comes from the Latin salto, and refers to their ability to dance with pantomimic gestures. It is supposed to be possible to stand at an appropriate distance and wave arms in such a way that these little spiders will signal back.
One particular huntsman - Delena cancerides - is rare among spiders. It is one of only 33 species of spider world-wide that exhibit social behaviour (as against `spider eat spider'.) If a woodpile is disturbed too often, there are plenty of other places to hide a huntsman or twenty. But it is still a shock to move a sheet of board or corrugated iron and find a horde of tiny huntsmen socially scuttling about. The big ones seek out the backs of car sun-visors, but thankfully they are solitary.

Not all of the species in a woodpile arrive alive. Some are killed in the crush, or lose Russian roulette with the chain-saw. Others are dead before the cut, victims of a burn-off. (The merchants call blackened firewood `Chinaman's wood'.) Both cutter and insect look for standing dead wood. It is a race to see which can reduce the tree to nothing first. One cutter tells me that wood needs to stand dead for seven years before it is dry enough to burn. Another says a dead tree can stay green for over ten years, giving the insects a head start.

So if the cutters don't get to a tree, the longicorn beetle might. This beetle seeks out trees that are stressed, damaged or recently dead. It lays eggs on the trunk, preferably in cracks or wounds. The larvae bore long tunnels into the trunk, secreting an enzyme that helps them to directly digest the cellulose. If you press an ear to the trunk you might hear them munching.

They are often mistaken for witchetty grubs, which they resemble except for the marked broadening of the `head and shoulder' region that gives them a body-builder shape. Longicorn grubs spend up to two years in the wood before pupating, leaving the wood filled with dark brown frass. They finally emerge from the pupa as blackish beetles with long antennae, almost wasp-like in appearance. The wood they leave behind is usually less than the highest quality for burning, let alone for timber, though this doesn't stop some wood merchants selling it as good firewood.

My great-grandfather, Alexander Grant, left accounts of his woodcarting in the 1860's. He worked the woodlands to the west of Sydney. Cutters would fell trees with axes and handsaws, drag them out by horse and chain, then carry off the sawn-up logs by horse and dray. It was at least a four hour trip to Oxford Street Sydney, where they would sell the wood. He writes:

"A pump used to be on the triangular piece of ground up Oxford Street for water carts to fill up. At this place would be sometimes 25 to 30 loads of wood, and people used to come there to buy."

These were rough times. Each night these same merchants would travel back along the Parramatta Road in convoy. It was some protection against both robbery and fatigue.

"To think that I was expected to keep awake after staying in Sydney till about 10 o'clock trying to sell out the wood, and then this brute (of a horse) would take 3 hours to walk home as he would not walk one bit quicker with an empty dray than a full one, and to sleep I would go in spite of all I could do."

To add injury to indolence, the `brute' also kicked Alexander in the face, shattering his jaw and disfiguring him for life. The woodcutter later spent a fortnight in gaol for cutting wood on the wrong side of an unmarked boundary. Nearly 50 years later (in 1907) he still rails

"We should not have gone to gaol. The wood was left where cut and we were sentenced for stealing - stealing what then to be tried by a personal friend of the plaintiff, and in his private room after court hours, does it look justice?"

Things were no better around Hobart, where wood and water rights were strongly disputed on the slopes of Mount Wellington. Here the blue gums (Eucalyptus globulus) were prized for cladding the whaleboats that worked southern waters in the mid-19th century. But they, along with stringy barks (Eucalyptus obliqua), were also used to make water races for the many mills that lined the Hobart Rivulet near what is now the Cascade Brewery. More than once the races were sabotaged, or the timbers stolen by woodsmen employed by rival merchants or millers.

The wood carters of today still dance with the law. By dint of their work, they have to fly by night. Short winter days of cutting, stacking, loading, unloading, repairing trucks and chainsaws; twilights and nights of delivering, handling the same wood for the fourth or fifth time, enduring complaints about how wet and cold their pampered clients are - the very clients who write them dud cheques. Suffering the snow, the mud, the impossible driveway, the irate customer, the predictably unpredictable weather. To survive, the species has developed its own canny instincts.

The taxman is the arm of the law most often capered with. My request to pay by cheque is met with a guffaw at the other end of the phone. The deal is strictly cash. And when I ask his name there is an eloquent pause. "Pete . . ." is all I'm told. (Say no more.) A few short years and he'll probably go the way of my last reliable supplier. Pat was as wide as he was tall - lived on ice-cream and coke, and used to complain about his health problems. If they cut him open they'd probably find longicorn grubs. At least he was honest.

The other kind are almost as abundant as the wood-dwellers they inadvertently deliver. I ask one where he gets his wood. "Up the bush" he says with a wry grin. His load is full of wattle and stringy bark. Stringy bark is a favoured food of Swift moth larvae (aenetus species). In turn these witchetties are an irresistible delicacy for the yellow-tailed black cockatoo (Calyptorhynchus funereus). These can kill a young stringy bark by stripping and weakening it in search of grubs. In other species of eucalypt it has been seen tearing large panels of live wood down the tree, then using the attached end as a platform on which to stand and munch the grubs exposed by its tear. The rollicking squawking birds can also make a mess of mature stringy barks, leaving mounds of the ropy bark littering the forest. Though the wood burns well enough, the mess made by its bark is nothing in its favour as firewood. When it's hollowed out by grubs it's even less attractive. Still some cutters can't resist finishing what moth larvae and cockatoos have begun.

Swift moths are not the only candidates for the name "witchetty". In different parts of Australia it has been given to the larvae of many different species, both beetle and moth. All have in common a large larva that is part of traditional Aboriginal food. They can be eaten cooked or raw, and are supposed to taste quite nutty.

But not all large moth larvae are edible. One of the largest, the giant wood moth (Xyleutes boisduvali) has a wing span of up to 250 mm. Though its abdomen is the size of a small sausage, its larva is prized as fishing bait rather than human fare. In Tasmania the larva of the wattle goat moth (Xyleutes durvillei) is also prized for fishing. The female moth lays masses of creamy yellow eggs in a blob of sticky fluid, onto the bark of wattle trees - hence its popular name wattle grub. The larvae burrow into the soft sapwood, where they can fatten up for several years. The prized grubs are commonly sold for $1.00 each, which fact is responsible for the mutilation of many young wattles. Between bait hunters, fire, cockatoos and larvae infestations, most wattles are short-lived. Their wood is not totally despised as firewood, but it generally burns too quickly and too hot.

Just as not all wood types are right for burning, so not all wood-dwellers are welcome in the home. One that can't be tolerated is the silverfish. A member of the thysanura order, there are 23 different species of silverfish in Australia. The most successful are the imported ones, whose ancestors existed for millions of years before the advent of paper. As with longicorn larvae, many species of silverfish secrete cellulase, which helps them to digest cellulose. But though they can eat wood the hard way, it can't be doubted that Herr Gutenberg's printing press did thysanura a great favour by encouraging the proliferation of paper made from easily-digestible wood fibre.

Our small black cat has developed a liking for silverfish. Whether indoors or out, she cannot resist chasing these piscatorial pretenders. I can't believe she actually digests the things - but usually the merest touch is enough to end their book-munching career. In the woodshed the assassin is more likely to be a spider.

A frequenter of the woodshed with even fewer friends than the silverfish is the scorpion. Ancient members of the arachnida, scorpions are thus related to spiders and mites. Ancient too is our fear of them, stemming first from their poison, but also from their symbolic power. In the bible scorpions rank with snakes as symbols of pain and desolation. "And their torment was as the torment of a scorpion when he striketh a man." (Revelation 9:5).

The venom of some scorpions has been found to contain toxins that can directly damage heart tissues. But the majority are no more venomous than those in my woodshed, they are simply larger. Cercophonius squama, the only variety in Tasmania, is rarely as big as a pen top; those in Palestine can be bigger than a penknife, and are thus able to inject more of their venom. So although fatal scorpion stings have been recorded, including in Australia, the majority have a sting about as painful as that of a european wasp (which has caused many more fatalities, and is far more aggressive.)

Scorpions are in fact shy of publicity, seeking dark, dry spots to go about their business. They can be found beneath piles of bark and leaves, or under rocks, though a nicely stacked load of firewood will do very well. As their eyesight is only up to distinguishing light from dark, they hunt by feel, using their large front claws, which bristle with sensitive hairs, to provide instant information about their prey. These can then be immobilised with the tail-mounted sting.
I split open a log and find one inside a cavity created by beetle larvae. The scorpion has gone there to hunt, and judging by the pile of shells, legs and other detritus, it has had a successful time. Not a fussy eater, it will consume beetles, spiders, larvae, even other scorpions, with the female often devouring the male after mating. It is said a male will never sting a female - a strange chivalry, if it is true.

The widowed female is a careful mother. She digs a semi-spiral burrow, and eventually gives birth to perhaps forty tiny white scorpions, which she will carry for weeks on her back, while they feed, grow and moult. When they are large enough to fend for themselves, they stay clear of their former home for fear of becoming mother's next meal. In more than 25 years of handling firewood, I have only ever encountered a dozen scorpions. And I have never been stung by one, "touch wood".

1 comment:

Kristi said...

Hi Peter,
This is really great. I love the way you've linked (links again) everything to the woodpile, including your great grandfather. Ive never found insects quite so interesting until now!