Dead wood is anything but dead

In a woodland, roughly one in five of the invertebrates you would find depend on decaying wood at some point in their life cycle. Fallen branches, standing dead trees and rotting stumps are the backbone of that habitat, and they are exactly what a tidy garden removes. A log pile is a simple way of putting some of it back, and it costs nothing beyond a corner of your plot and a willingness not to tidy up.

The principles are straightforward. Dead wood holds moisture, slowly releases nutrients and creates layers of dark, humid shelter that almost nothing else in a garden provides. Unlike a compost heap, a log pile is not designed to break down quickly. You are aiming for a slow, decades-long decay, and the creatures that move in at year ten are often different from those at year one. That gradual change is what makes it so valuable.

Choosing the right spot

Siting makes more difference than construction. Aim for dappled shade with at least one side catching sun for part of the day. Full sun dries the timber out and slows fungal decay, whilst deep shade stays cold and is less attractive to the basking insects, slow worms and grass snakes that log piles often attract. A position at the back of a border, beneath a hedge or below a mature deciduous tree is close to ideal.

Keep the base in contact with bare soil rather than paving, gravel or membrane, because the damp soil-to-wood interface is where the whole system gets going. Avoid hollows that sit under water in winter, and don't put the pile against a wall of the house where rising damp might become a worry. Leave it undisturbed: a pile tucked behind the shed and forgotten is far more use than one in the middle of a lawn you mow every fortnight. If you have the room, two piles in different situations will support a wider range of species than one large one.

What timber to use

Native broadleaved wood is best: oak, beech, ash, birch, hazel, willow, field maple, apple and cherry. Mixing species and log diameters is better still, because different timbers rot at different rates and support different fungi. Oak and beech last for years; birch, willow and sycamore soften quickly and will be colonised first.

What to avoid is just as important:

• Treated, painted or stained timber, along with MDF, chipboard and most pallet wood, which may contain preservatives or adhesives.
• Freshly felled green wood in large quantities, which can be slow to colonise; a mix of seasoned and fresh is fine.
• Anything from a tree with a notifiable disease in your area, such as ash dieback, unless you have checked local guidance.
• Conifer offcuts in bulk, which are acidic and less appealing to many invertebrates, though a few branches mixed in will do no harm.

Leave the bark on. It is where a great many beetles, larvae and hibernating insects spend the winter.

Building the pile

Start by loosening the soil where the pile will sit, so the bottom layer makes direct contact with earth. Lay your largest logs first, side by side and slightly apart, so gaps and crannies remain. Stack successive layers at alternating angles, log across log, like a very untidy game of Jenga. The aim is a loose structure full of voids, not a neat wall.

Add variety as you go:

• One or two vertical stumps, buried a third of their length in the ground, which mimic a standing dead tree and are especially attractive to beetles whose larvae need buried wood.
• Smaller branches and twigs stuffed into the gaps, along with a few handfuls of leaf mould or soil to help things get started.
• A hollow or two left at the base, which hedgehogs, frogs and toads will use as shelter.
• A log or two drilled with holes of 3–10 mm and 10–15 cm deep, on the sunny side, for solitary bees such as red mason bees.

A pile around a metre high and a metre and a half wide is plenty. Anything larger is a bonus, but even a modest stack of half a dozen logs is worth doing.

What will move in

The first arrivals are woodlice, millipedes, centipedes, earwigs and spiders, followed by beetles and their larvae, many of which spend several years in the wood before emerging. Stag beetle larvae, where you are lucky enough to have them, need buried rotting wood and can take up to seven years to develop. Fungi appear on schedule too, softening the timber and converting it into something other organisms can use, and their fruiting bodies feed slugs, beetles and small mammals.

Above that, the pile becomes a nursery and a refuge. Slow worms and grass snakes bask on the sunlit side. Hedgehogs nest in the base and may hibernate there. Bats roost in the deeper crevices of larger piles. Later still, moss, ivy and hart's tongue fern colonise the shaded logs, and the whole thing stops looking man-made and begins to look like a piece of woodland floor that happens to be in your garden.

Looking after it, or rather not

The main task is restraint. Don't turn the pile, don't tidy the leaves that collect around it, and don't move or burn it between October and March, when something may well be hibernating inside. Keep it damp in dry spells by watering the surrounding soil rather than the wood itself, and top it up every few years with a few fresh logs laid on the top, so the structure ages unevenly and offers both newly dead and well-rotted timber at once.

If a log sprouts a sapling or a cap of bracket fungus, leave it. If the pile slumps a little, that is the point. A good log pile is a habitat that keeps giving for a decade or more, quietly working away at the bottom of the garden whilst you get on with the rest of it.