1.
The Zombie Forest
Pinus sylvestris, Scots pine
GLEN LOYNE, SCOTLAND: 57° 04' 60' N
As the ice retreated to higher ground at the beginning of the current interglacial period, the boreal forest set off in pursuit. Plants that had not been seen on the islands of Britain for thousands of years began, gradually, to return. Ice persisted on the uplands of north Wales and the Highlands of Scotland, but in the valleys and the plains, lichens formed a crust on the exposed rocks. Then came mosses with their creeping fur, laying the ground for grasses and sedges first, soon to be followed by the pioneer shrubs of hazel, birch, willow, juniper and aspen. This boreal system worked its way north, across the land bridge where the English Channel now is, a sweeping tide of green on the heels of the ice, the cocktail of early seeds dispersed according to the natural cycles of wind, rain and the migratory patterns of animals, including humans.
Ten thousand years later, I follow. Pointing the car north from Wales, I head to where the map says the treeline has come to a halt at its present position: Scotland. Driving to Fort William through the spectacular soaring valleys along the west coast of Scotland, the rocky outcrops of the peaks appear stationary, like the roof of a cathedral merging with the sky. The rich green slopes roll back and forth with every bend in the road; scree tumbles in long runnels like waterfalls from hidden lakes of rocks high above. Sunlight shears the view, one minute blinding, the next revealing a promised land.
It is not until I am actually there that the contradiction strikes: I am searching for the upper limit of the forest, but where is the forest? Scotland’s forbidding hills, rank upon rank of shadowed slopes rising out of the mist, are such a durable a sight in collective memory and culture it is almost impossible to imagine them otherwise, and yet Britain was once, briefly, an island of trees. Caledonia, as it was named by the Romans, means “wooded heights,” but its “great wood” has become a mythical thing. Scotland’s bare hills are both epitaph and warning: this is where the commodification of nature leads.
To ask what is happening to the treeline in such a ruined landscape is a profoundly political question. On paper, Scotland is held to be the southern and western limit of the Arctic treeline in Europe; estimates based on temperature and growing seasons suggest that here it should be at 2,300–2,400 feet.1 Stumps have been excavated at 2,600 feet dating from a slightly warmer era four thousand years ago.2 But how the treeline is responding to warming now is hard to say because nearly all the trees were cut down. Efforts to restore Scotland’s great wood are under way, “re-wilding” the hills and planting trees, partly to allow them to find their level and re-establish a natural transition zone between the forest and the moor. But such changes are controversial. How we see the present and the future often depends on our understanding of the past. What is natural? What is being restored? Meanwhile, as humans debate ecological history, global warming gathers force, threatening to render our meager response irrelevant.
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The treeline’s first wave, or primary, vegetative cover after the last ice age resulted in a patchy forest that the foremost historian of British landscape, Oliver Rackham, calls wildwood.3 This was a dynamic shifting community of plants—at its southern end connected to mainland Europe by the land bridge, and at its northern frontier petering out into the moorland tundra of the “flow” country in the far north of Scotland and the scattered rocks of the Hebrides, where the dry cold of the Arctic polar vortex wrestles with the Gulf Stream for influence.
This wildwood was rampant but precarious. Birch was quick to establish but transitory, giving way to other, bigger and bolder trees. As the evolving society of the forest worked out its own logic, a steady state would emerge with a particular tree or trees dominant. In much of southern England this was lime, in the north and Wales it was a mix of hazel and oak. In the Highlands of Scotland the apex tree was originally oak. But the steady state of the wildwood could be upset and tipped into another cycle by an influx of a new species or a change in the weather. The introduction of the pine was one of these.
Around 8500 BCE pollen records show Scots pine (Pinus sylvestris) arriving suddenly across Britain, colonizing a corridor up the west coast of the British Isles, nosing its way into the inlets and fjords of Scotland and then across the straths and valleys and up into the mountains. Pine out-competed the birch and oak that had generously worked up sufficient soil for it to flourish. So successful was the pine that the birch disappeared almost completely for thousands of years, surviving only in a remnant zone in the flow country north of what is now the city of Inverness.
This pine wood spread across Scotland, reaching its apex of around 80 percent of the land area, according to Rackham, around 4500 BCE. Recent archaeology, pollen analysis and even the 7,000-year-old bones of pine trees preserved in bogs have fed debate about the scale and the fate of Scotland’s once magnificent wildwood.4 Conservationists are seeking a record to guide their attempts at “ecological restoration.” Opponents are seeking evidence that the trees were eliminated through natural causes and that the current status quo of grouse moors and deer parks is just as deserving of the designation “natural.” At issue, it seems, is one vision of nature over another, neither of which attributes much influence to humans for creating the shape of the landscape in the first place, and yet the history of humans and the history of the forest is deeply entwined.
Before driving north, I read a scientific paper by Lithuanian researchers demonstrating that the DNA of the Scots pine in the eastern half of Scotland came from a refugium—a place where species survived the last ice age—near Moscow around 9000–8000 BCE.5 Previous DNA analysis has shown that the surviving pines in the west of Scotland came from the Iberian peninsula in modern-day Portugal and Spain. In both cases the seed migrated to Scotland on timescales hundreds of times faster than is possible through natural succession. The most likely vehicle for such rapid migration was humans.
There is a myth in Celtic folklore—with an apparent grain of truth—that when the Celts colonized Scotland they met Ukrainians coming the other way. For the Celts, the pine was a sacred tree with a myriad of uses. The pine was ailm in the Celtic alphabet, the ogham script, and it is very likely that they brought it with them from Ireland and Wales. It was perhaps sacred too for the mysterious Ukrainians, who were part of the Celtic kingdom, “the people of the Danube” in old Irish, the only others with red hair. For humans so tied to nature and reliant on plants it would make sense to travel with your own habitat. Something twenty-first-century humans might soon wish we were able to do.
The result, in the present day, is two distinct genetic communities of Scots pine in Scotland divided by the Highlands. They have yet to cross-pollinate and conservationists are keen that they do not since the genetic and chemical distinctiveness has consequences for other species that rely on the keystone of the pine. Insects like wood ants, for example, can taste differences in resin and will choose particular trees as a result. Leaf chemistry, flower timings and growth forms are all different. The crested tit remains east of the Cairngorms, embedded in its environment. However, the conservationists needn’t worry yet. The risk of interbreeding is minimal since the fragments of surviving forest are spread out and very small. Less than 1 percent of Scotland’s old-growth pine woods remain.
Rackham argues that the pine wood never stretched from shore to shore, but it certainly covered most of Scotland until Mesolithic humans began to clear the forest for agriculture, hunting and construction. Managing the forest through felling, clearing or burning for game played a role in creating biodiverse habitats of heath and moor, but also set the stage for the creeping blanket bog that has become upland Britain’s signature landscape. The bog is, in a sense, a ruined ecosystem as tree clearance has allowed minerals and iron to be washed into the lower layers of the soil, creating a pan impermeable to water. Unable to drain, the tundra-type landscape becomes waterlogged, and plants do not fully decompose, forming peat.
The pastoralist indigenous crofters, who farmed the Highlands till the clearances of the eighteenth and nineteenth centuries, traditionally moved their cattle between the lowland forest and the moor. The clearances and the subsequent expansion of Victorian shooting estates for grouse and deer are often blamed for the deforestation of the Highlands, but while heather burning and overgrazing by deer in the absence of apex predators like wolves, lynx and bears did indeed prevent the trees from coming back, much of the open upland landscape had already been formed by clearing all the trees.
Copyright © 2022 by Ben Rawlence