We're deep into Russell's domain at Forsinard, the Royal Society for the Protection of Birds' reserve in the heart of the Caithness and Sutherland peatlands, often known as the Flow Country. The Society owns 8,398 hectares of peatland around Forsinard, and early this year acquired a further 3,845ha at Blar nam Faoileag in neighbouring Caithness. To the ignorant eye a fairly monotonous-looking expanse of moorland, broken by lochs and pools, this is in fact part of one of the largest and most intact areas of "blanket bog" in the world, where some 8,000 years' accumulation of peat supports a unique and delicately balanced environment. Walk into it, ideally accompanied by the expert eye of Russell, and you feel its very structure spring beneath your feet, you enter a landscape with a primeval beauty all of its own.

Time comes dropping slow at Forsinard, and it lies in layers. Earlier, in the pick-up with Russell and his assistant James Plowman, as we bumped along a forestry track from the RSPB visitor centre at Forsinard Station, I could see wizened, ash-coloured pine roots protruding from the peat embankments on either side, where they had been buried as long as 4,000 years ago, gnarled relics of a period where the climate warmed and this area became covered by pine woods. Further down, glinted fragments of 8,000-year-old birch. The peat reads like a great, layered document. Delve into it: here you'll find a layer of volcanic ash laid down when an Icelandic volcano, now known as Hekla 4, blew its top 4,000 years ago (you'll find the same ash layer in North America), there you'll discover charcoal that indicates when man first settled in this area.

Then there's the pollen. Drifting into the peat bog over eight millennia, it has been preserved and can be "read" and dated under a microscope. "In a lump of peat the size of your thumb," says Russell, "you can find up to half a million grains of pollen. That's quite a few megabytes of information."

It is its more recent history, however, that has threatened to put in jeopardy the Flow Country's delicate ecosystem of bog pools - the "dubh lochans" - and surrounding peat-dependent growth. It started in the Sixties, when the government offered grants to assist farmers and landowners in installing hill drains. Then in the Eighties a widely publicised row blew up over the private forestry investment that started laying dark slabs of sitka spruce and lodgepole pine across the boglands. In fairness, says Russell, this was before the importance of the peatlands had been fully realised. These days, they are sometimes compared to rainforests for their importance as absorbers of carbon that would otherwise pollute the atmosphere. On the other hand, they also release quantities of methane, regarded as a "greenhouse gas".

Six thousand hectares of forestry were established on Forsinard estate over a five-year period during the Eighties. Most of these he says, have been sold off since by the original investors to other concerns. The RSPB is now involved in buying up blocks of these trees, many of which are too small to be commercially viable. Unable to dispose of them any other way, the reserve uses them to block up the drainage channels cut for the forestry, gradually restoring equilibrium to the disturbed bog. "It might take 1,000 years for the forestry furrows to disappear, but the peat's been going here for 8,000 years, so that's not really a problem," says Russell philosophically, although clearly he would rather the trees weren't there at all. The Flow Country has been proposed as one of UNESCO's World Heritage Sites, with which status it would join the likes of the Great Barrier Reef, the Great Wall of China and the Taj Mahal. "So having forestry here, in a way, is like having a McDonald's in the foyer of the Taj Mahal."

The peatlands of Caithness and Sutherland contain 39 SSSIs (Sites of Special Scientific Interest). Russell has been at Forsinard since the RSPB acquired the estate in 1995, and his work involves everything from mowing the grass at the visitor centre to helping negotiate land purchase. "We get about 5,600 visitors a year, putting a minimum of œ185,000 into the local economy. That's a very useful figure to have, because it tends to make local politicians take you that bit more seriously" - also, he adds, because the conservation vs forestry debacle in the Eighties left some bad feeling among the locals. "However, I think the fact that the RSPB has a stake in the ground has done a lot to change perceptions. They see how we've run Forsinard over the past four or five years."

"Forsinard?" the ticket inspector had said on the three-hour train journey from Inverness. He had chortled ghoulishly: "The midges are real bad up there today, sir. Ferocious, they are." Things hadn't looked good since I'd walked into the station for the 7am Thurso train and noticed the destination board showed 15 stops before Forsinard. The three-hour journey wasn't eased by the fact that, in contrast to the beneficent sunlight that had bathed the Highlands the evening before when I'd travelled up from Edinburgh, the Cromarty and Dornoch coasts were blanketed by haar, prompting me to wonder whether I was ever going to see those famous Sutherland skies. And now Scotrail was issuing midge warnings.

However, as the lush lands of the Strath of Kildonan gave way to open moorland dotted with Scots pine, the mist started to disperse. And by the time I stepped on to the platform at Forsinard, the gold, green and russet weave of the great bog that undulated all around was glowing in the sun.

Forsinard. It's a Norse-Gaelic hybrid for "high water", and it is the abundance of water, held in the peat bogs - which can be as much as 98 per cent water to 2 per cent peat -that gives the place its unique character. The sphagnums don't die as such, but keep growing at their tips. In the airless, soggy, acidic environment, beneath this spongy living surface, the organisms which normally cause decomposition can't exist, so the layers of dead moss build up into what we call peat, sometimes six metres deep. This pool-riddled bogscape covers half of Caithness and Sutherland and constitutes some 13 per cent of the world's blanket bogland. To see anything else like it, you'll have to take yourself off to the likes of Newfoundland, Alaska or Tierra del Fuego.

As Russell and I plod across the bog, engaged in a scoter survey, he points out plants, often rare elsewhere, that thrive here; bonsai-like dwarf birch and aromatic bog myrtle, or the bog-bean stems that criss-cross the surface of pools, inevitably cropped to a deer's reach from the edge. He stops before a mossy hummock and gives me a break-down of its vividly-hued microcosm: a matrix of sphagnum, of course - gingery-brown sphagnum fuscum in this case, through which sprout heather and hare's tail cotton grass and sprigs of pretty yellow bog asphodel; also the glistening red leaf clusters of a sundew, which ensnares insects for the nutrients it won't get from the peat. We note with some satisfaction that this particular one is doing a good job with midges, although, as we know to our cost, it still has several trillion to go. It is hot and sticky, and the ticket inspector's prophecy has proved horribly true, with legions of clegs thrown into the bargain.

A frog leaps out of our way into a pool and Russell warns me at one point to watch out for adders under my feet. Lurking in the brown depths of the pools, with extending jaws as fearsome as anything in Alien, are the voracious larvae of various dragonflies, the adults of which skim across the water, big rattling hawkers and smaller, glittering darters and damselflies. Bird life, of course, abounds here - including 66 per cent of the European Community's greenshanks, 35 per cent of its dunlin population and 17 per cent of its golden plovers, although with the breeding season over, most have moved to the coast. Predators such as merlin, harrier and even golden eagle patrol these wide-open spaces. The intruding forestry also harbours crows and foxes, which provide a threat to the eggs and young of the bogland's indigenous species.

The scoter count is not going well. The little black duck is common as a winter visitor to British coasts, but there are only about 100 breeding pairs in the country, of which 14 pairs are at Forsinard. But with a poor survival record for the broods. Russell and Plowman are trying to find out what's happening to them. We've seen none, until towards the end of the afternoon when, coming away from a small loch, Russell spots a family of six on the far side. We sit down to watch, joined by a convention of highly interested midges.

"Well, we've at least got one brood that's performing," he says. "That's good news."

But of the bird life, what lingers on in the memory during the journey back to Edinburgh is the trio of red-throated divers we came across, two adults and a chick, cruising in a pool like displaced plesiosaurs. Rain geese, the locals call them, and at our approach they let out a long and eerie cry. Rain to come, or was it simply the high and lonely voice of the Flow Country?