48

I wait among pine trees in the last car park in the glen. I'm on the lookout. I have a rendezvous.

A white van with the words ‘Forest Research’ on the side comes winding slowly through the trees, the red-bearded, freckle-faced driver glancing about him.

‘Joe?’

‘John?’

We shake hands.

It's August but too early in the morning for the tourists to be about – the bikers, the hikers and the random strollers. We have the forest to ourselves.

We cross the Affric River, dark and still as it flows under the wooden bridge on its way to the great loch Beinn a'Mheadhoin, then plunge into an undergrowth of long grass and straggly heather, the heather bells just beginning to show colour. Who else comes here, off the beaten track, now or at any time? A faint blush of purple is showing on the surrounding slopes. Behind us rears the prow of the lesser Sgurr na Lapaich (two hills in Strathglass share that name), a silent watcher.

The ground is broken and hummocky, the humps festooned with lush vegetation – mosses, blaeberry, cowberry and calluna. We brush through fine-spun, gauzy spider webs, almost invisible, which brush our faces in passing like soft fingertips. A wood ant, bigger and clumsier than the familiar garden kind, flops onto my hand. Joe says old forest like this is its natural home.

We reach a spot in open woodland where, in the near vicinity, a few spreading Scots pine grow alongside a birch or two dripping with hairy lichens, an alder and a spindly rowan. At our feet, a fallen trunk, species unknown, lies felted with vegetation, in slow decay. The remains of a pine tree, which snapped 10 feet from the ground in a winter gale, thrusts up a branch tufted with a single small mop of foliage.

This is Joe's research patch – a sheltered spot in the area marked Pollan Buidhe on the map.

He wanders among the trees, stopping to peer through a lens the size of a thimble, seeking out lichens and mosses lodged in crevices in the bark or drooping pendulously from branches. He hands me the lens and I struggle to focus (there's a knack in it). Suddenly, the blur resolves into a tiny forest of delicate fronds and fluted spicules, a secret landscape emerging from mists. He names this as a species of bryoria, Bryoria fuscescens in botanical terms, not by any means a rarity – it's all around. Joe's after something a bit more special.

The morning becomes a lesson in botany. Parmelia saxatilis – ‘brown branching hairy kind of stuff. It grows on rocks as well as trees. Saxatilis is Latin for growing on stone.’ A mass of pale yellowy-green moss draped over a rock is Racomitrium lanuginosum, soft and spongy by the look of it but dry and fibrous to the touch. Swathes of Alectoria sarmentosa hang from a broken trunk and, close by on a lone pine atop a bluff, Imshaugia aleurites – a presumed indicator of woodland longevity. Its presence here helps, in a small way, to reinforce the theory that this pinewood has grown in unbroken succession for centuries and possibly thousands of years.

Elsewhere in Pollan Buidhe, other scientists are busy. Helen is studying what the pollen grains stored in the soil can tell us. With her is Alex. ‘I'm the partner,’ says he. ‘I'm here to help carry the things.’

The sun shines, it's hot, a light breeze stirs the foliage. Pollan Buidhe on a summer's day is a Forest of Arden, except that Shakespeare's Arden never knew midges. Alex, who's small and dark, pulls a gauze veil over his face and trim beard for protection against the tiny bloodsuckers. Helen seems oblivious. I douse myself with insect repellent and we head into the undergrowth.

This cup-shaped hollow in Pollen Buidhe is ideal for Helen's purpose, which is to chart the vegetation that has grown in Affric through the ages. The clues are in the tiny pollen grains preserved for many centuries in the thick layer of peat that lies beneath the vegetation. Here the peat slowly accumulated to a depth of many feet, forming a sink into which a constant rain of pollen fell. Since no stream flushes through the ground the sediment of ages has remained undisturbed and little has seeped away. The picture is clear.

The ‘things’ Alex helped to carry are mainly a bundle of long tubes. Helen takes the first tube and they screw it into the ground, adding another and then a third as the probe sinks deeper. When the full depth is reached, they withdraw the tubes, now filled with a core of dark peat, a visible record of the past. Each centimetre marks the passage of ten years – a metre's depth is a millennium. Bits of fibrous material survive even at that depth but it's the pollen, invisible to the naked eye, which will provide the information Helen needs.