Wild Barcelona: Fruits of decay

Steep paths send you plunging rapidly into the deep valleys of Collserola, where sunlight mingles with the damp mist, infiltrating fans of slanting tree shadows. The woods have recovered the rich autumnal smell of decomposition. Mushrooms are emerging, thrusting aside the leaf mulch, though some of the most colourful fruits of decay are at eye-level.

Semi-circular conks jut out of dead or weakened trees. Named shelf fungi, after their perpendicular angle of growth, these solid, dense structures can last for years, having absorbed the hardness of the wood they grow on. The red-banded polypore, for instance, grows a new spore-containing layer each season, allowing you to count up its years. The result is a multi-coloured conk of white, yellow and red.

In Castilian, shelf fungi are known as yesqueros—tinderboxes. While the surface is inflammable, the interiors can smoulder for days, allowing them to be carried around like primitive cigarette lighters.

Most vibrant of all the yesqueros are the turkey tails, thin and leathery, with a fine velvety surface. Infinitely varied, they produce rings of startling blue or green among the browns and greys. In this species, the contrasting bands of colour reflect growth spurts rather than years. They can smother a fallen trunk or tree stump with exuberant clusters, while, out of sight, microscopic threads penetrate deep into the wood, armed with enzymes to digest it. Fungi can break down the toughest of organic material, including hooves and shells, so a tree is no big deal.

As well as recycling essential nutrients, and stopping a forest choking on its own debris, shelf fungi help provide homes. It’s not unusual to see a woodpecker’s hole drilled directly underneath a protruding conk. It’s not that the birds want a porch roof to keep off the rain but simply that fungus-infested wood is clearly easier to chisel.

Lucy Brzoska runs nature tours and writes for www.iberianature.com