Systems
11.12.2019

Refilling the Carbon Sink

Long seen as wastelands, Scotland’s bogs are now the scene of an intense restoration effort in which millions of exotic trees are being felled to fight climate change.

The bog at Forsinard stretches to the horizon, a vast mosaic of greens and browns. The tallest plants here grow only ankle high, but even so, walking requires careful attention. Hummocks covered in heather (Calluna vulgaris) or cotton grass (Eriophorum spp.) offer lumpy but secure footing. Soggy patches of Sphagnum moss are less predictable: They can bounce back underfoot like a trampoline, or give way and allow an unwary hiker to sink into the muck.

Roxane Andersen makes good time as she crosses this deceptive landscape, her feet encased in knee-high waterproof boots, finding the higher, drier spots with little effort. Andersen, a peatlands scientist at the University of Highlands and Islands in Thurso, Scotland, strides over to a tower stacked with electronic boxes interconnected by a web of cables and tubes, a strikingly alien presence in this wide expanse of flat wetland.

These bogs, in northern Scotland’s Flow Country, are deceptive in more ways than one. Beneath the moss and the heather and the sedge lies one of the planet’s largest surviving expanses of peat—a nutrient-poor, carbon-dense mass of partly decayed organic matter. Andersen has been working to document the peatland’s hidden strength: It has a prodigious ability to lock away carbon, making it an important resource in the fight against climate change.

Until recently, most people viewed bogs, like the ones Andersen studies in the Forsinard Flows Reserve, as a waste of space. In Great Britain and beyond, people have drained large swaths of peatland and converted it to pasture or crop land for centuries. An estimated 80 percent of Britain’s peat bogs have been damaged or destroyed. Today, however, Britain is on the leading edge of a global peatland-restoration movement, and the program at Forsinard is among the largest of these efforts.

Peat is made up of partly decayed plant parts, pickled in acid released by living Sphagnum moss. Plants in the vast bog at Forsinard are both rooted in peat and laying down new peat as time passes—a process that began about 10,000 years ago at the end of the last Ice Age. A mass of healthy peat is about 90 percent water, which it filters and purifies, and houses a small group of specialized plants that have adapted to the extreme conditions of a nutrient-poor, waterlogged, acidic habitat.

Andersen tracks the greenhouse gases that the ecosystem breathes in and out using eddy covariance technology. “Eddy flux covariance towers look very complicated,” she says, “but the principle is simple.” The instruments sample eddies of air flowing over the bog every 30 seconds to track the amounts of carbon dioxide and methane absorbed and released. The automated system gathers data day and night, unless powerful winter winds damage the machinery or the corpses of the bloodthirsty Highland midges that swarm here in summer clog its passages. Andersen’s data have shown that undisturbed bogs make strong carbon sinks, while drained areas release significant amounts of carbon into the atmosphere. She and her colleagues are using these results to piece together best practices for restoration.

Andersen reaches down and grabs a handful of the dainty Sphagnum moss that dominates—and creates—healthy peat. Its living tips are red-brown, tinged with bright green. “I absolutely love Sphagnum,” she says. Then she closes her fist and rivulets of water pour through her fingers.

The moss’s quirks both ensure its survival in this harsh, soggy habitat and facilitate its role as an ecosystem engineer. Sphagnum is a living sponge, Andersen says, able to absorb twenty times its weight in water. Interspersed among its bright green photosynthetic cells is a matrix of hollow cells that holds onto moisture and releases it gradually, ensuring the surroundings stay wet. The moss acidifies its environment by producing hydrogen ions. And it releases a chemical compound, called sphagnan, that helps slow decay. The result is a watery world that allows peat to build up.

Scientists now know that peat ecosystems are the most powerful carbon sinks on Earth. They are capable of holding twice as much carbon per hectare as a pristine redwood forest, the planet’s second-most carbon-rich ecosystem, says Hans Joosten of the Greifswald Mire Center in Germany. Scotland’s peat bogs, which comprise more than 20 percent of the country’s land area, hold about 75 percent of the carbon locked away in all British soils and vegetation—which is why their restoration has become such a priority.

The beauty of the peatlands is subtle. Joosten and others call them a Cinderella habitat—hardworking, so far as carbon storage and water purification go, but easy to ignore. “It tends to be perceived as a brown, drab blanket of wetness,” says photographer Peter Cairns, who admits to a love-hate relationship with the Flow Country. He’s trudged for miles through the bog, lugging heavy, awkward equipment in his efforts to capture its essence. “It’s flat, wet, hard going,” he says. “It’s a very difficult habitat to work in, and a difficult story to tell.”

But Cairns also knows it’s an important story to tell. In the 1980s, the British government subsidized a blitz of bog drainage in order to plant exotic trees for marketable timber. (Since World War I, when a lack of available timber hindered Britain’s war effort, the country has viewed creating forests as a national good.)

The resulting plantations of lodgepole pine (Pinus contorta) and Sitka spruce (Picea sitchensis), species native to North America, failed to thrive. The Flow Country had been treeless for thousands of years for good reason. Peat soil is often too acidic and nutrient-poor to support healthy trees, and the Flow Country endures howling winter winds up to 90 mph, which can stunt their growth or yank them out by the roots.

Native bog plants, in contrast, have evolved to thrive where nutrients are scarce. Sphagnum absorbs nitrogen with great efficiency, and each plant in a carpet of moss continuously recycles nitrogen from its dying base to its living tips. Heather, which grows in a stunted form on the bog, depends on the mycorrhizal fungi that live in its roots to extract nutrients from the peat. Sundews (Drosera spp.), carnivorous plants whose sticky, tentacled leaves stick up like tiny space aliens, acquire their nutrients by trapping passing insects.

During the forestry boom, the government offered grants to those interested in plowing up natural bogs to plant trees, and provided tax relief to wealthy forestry investors. Overall, 67,000 hectares—17 percent of the ancient peatland of Flow Country—was drained. Some of Britain’s richest citizens reaped impressive profits, but usable timber was rarely produced. In most cases, the plantations have grown only spindly trees that are unsuitable for lumber, so are used as biofuel or simply abandoned. While these ill-conceived forests haven’t produced much wood, they did trigger one of the fiercest environmental battles in British history.

Richard Lindsay had just begun to survey the life of the Flow Country when the government’s timber incentive program began. He and his colleagues at the UK Nature Conservancy Council hurried to record the beauty and biodiversity of wild Flow Country bogs moments before plows began ripping them apart to create tree plantations. “We were literally running along right in front of the plows,” he remembers. “We would go and survey an area one day, and go back the next day to see the plows [pass] right through the area that we’d just surveyed.”

Living in pup tents, walking long distances across the formidable bog, Lindsay’s crew explored an intricate world where water equaled life. They found a community of different Sphagnum and sedge species—some adapted to live on the raised hummocks and ridges, others thriving in the lower, soggier spots. They discovered that the rolling terrain hid mazes of pools, where diving beetles moved busily between the surface and the bottom, caddisfly larvae trundled along inside protective shells they’d built from bits of clay and pebbles, and newts and frogs fed on the insects.

This aquatic abundance also supported droves of migratory birds. Ornithologists who rushed to study the Flow Country found a spectacular array of breeding species. In April, when the migratory waders arrive, the bogs come alive with graceful birds flying, calling, and soon after, incubating their eggs. Throughout the spring and summer, wading birds stalk the edges of bog pools, picking off prey to feed their chicks. In addition to offering rich hunting grounds, the bog provides ideal camouflage. The grey, white, and black plumage of common greenshanks (Tringa nebularia), large sandpipers named for the light-green hue of their legs, disappears against the sedge and heather. Golden plover (Pluvialis apricaria) hatchlings look like little more than a heap of Sphagnum moss when hunkered down atop the bog.

The region is essential habitat for breeding birds. The researchers found that the Flow Country hosted a startling 66 percent of Europe’s breeding greenshanks, 35 percent of the dunlin (Calidris alpina), and 17 percent of all European golden plovers. Divers—elegant, sharp-billed birds known as loons in the U.S.—also raise families here: Black-throated (Gavia arctica) and red-throated (Gavia stellata) divers nest among the small lakes of the blanket bog, often crossing the bog pools with young chicks on their backs.

But as plantations grew up, the conifers formed dense, impassable thickets. Predators began to move in—hooded crows (Corvus cornix), red foxes (Vulpes vulpes), pine martens (Martes martes), and others that birds of the bog had never encountered before. The danger zone stretched hundreds of meters around each plantation, eliminating potential nesting habitat for unknown numbers of dunlin, golden plover, and willow ptarmigan (Lagopus lagopus).

The new plantations also brought other threats to the region’s native species. To prepare their land for timber, plantation owners plowed up the bog, killing off the blanket of native plants that build peat and hold water on the landscape. Water drained away, eroding gullies and drying out the peat.

Lindsay, now head of environmental and conservation research at the University of East London, sees bogs as superorganisms in which the plants work together to manage the flow of water and keep the system healthy. “If you cut an artery in your leg, it’s a small wound but can have profound effects on you,” he says. “In the same way, cutting a small part of a bog can have profound impacts because its entire hydrology is connected.”

Armed with new data from these scientific surveys, a group of advocates led by the Royal Society for the Protection of Birds (RSPB) and the Nature Conservancy Council launched a full-fledged battle to protect the Flow Country bogs. Finally, in 1988, after about 190,000 hectares (470,000 acres) of UK bogs had been drained and planted with trees, the government ended its financial incentives. By then, the Flow Country had been severely impacted. RSPB acquired part of it—the 21,000-hectare (51,900-acre) Forsinard Flows Reserve—in 1995. Within four years, an additional 146,000 hectares (360,800 acres) of Flow Country bog had been designated as a Special Protection Area under the European Union’s Bird Directive.

At that point, the anti-plantation movement was driven solely by conservation concerns—Lindsay and the others were working to protect the peatlands’ native species. It would still be a few years before ecologists came to appreciate another trait of the bog: It stores tremendous amounts of carbon, but only if it’s healthy—and wet.

When bogs are drained, air exposure speeds up peat decomposition, causing the bogs to hemorrhage carbon into the atmosphere. “Peatland switches from a carbon sink in natural conditions to a carbon source in drained conditions,” Andersen says. “Carbon that has taken thousands of years to accumulate could be released in much less time.”

Major farming regions in Europe and North America—including the Midwestern corn belt and California’s Central Valley—lie on drained peatlands that have been spewing carbon for centuries. “You cannot see these emissions,” Joosten says. “A meadow with cows looks like a rich agricultural landscape. [But] this area emits the same amount of CO2 per hectare as driving 135,000 km (83,885 miles) in a mid-size car.” He calculates that drained peatlands produce about 6 percent of all human-generated greenhouse-gas emissions. “That’s an enormous amount for a source that had not been recognized before,” he says.

Today, Scotland is pouring cash into eliminating the very forests that people were paid so generously to plant just decades earlier. The country has spent millions so far, including more than £10 million ($12.85 million) for restoration work at the Forsinard Flows Reserve. The Scottish Government’s Climate Change Plan aims to restore 250,000 hectares (617,800 acres) of peatland by 2030.

Because drained peatlands give off carbon 20 times faster than intact peatlands can sock it away, the priority during restoration efforts is to re-wet the ground. At remote forestry sites, the trees are often so small that it would cost more than the timber is worth to truck it away. In these cases the felled trees are left to rot in the plow furrows. Andersen and others have learned that the felled trees’ rotting remains boost nutrient levels in the soil, encouraging the growth of tall grasses that can outcompete native plants.

Over the past two decades, the scientists have also gained other important insights about the restoration process. Many of their lessons have been learned at a location within the Forsinard reserve known as Talaheel—one of the first sites to be forested and one of the first targeted for restoration in 1998. Before the trees were planted, foresters dug up the peat using a special plow that scarred the bog’s surface and left a pattern of deep furrows alternating with ridges of piled earth. They planted trees on the ridges, while the furrows allowed water to flow out and away from the area, ultimately sinking into drains at the edges of the plantation.

Early restoration workers blocked the collector drains so the water table could rise again. In the wet ground, native bog plants, such as heather and cotton grass, began to take root. But Andersen and her collaborators found that, over time, the ridges and the furrows were colonized by different plants. The higher, dryer ground hosted grasses, sedges, and heather, while Sphagnum moss dominated the wet depths. Based on their findings, restorationists now flatten the plow ridges and block each furrow with a dam of cut peat to keep the entire site wet. 

Bog restoration takes time. Some of the more recent restoration sites look grim, like open graves for stunted trees. In many places, bleached and broken branches still lie heaped in the old plow furrows. But Andersen knows change is coming.

Today, sixteen years after restoration began, Andersen has found that Talaheel has switched from carbon source to carbon sink, capturing about 60 percent as much carbon per hectare as the pristine control site. “Even though some of the plants growing there are not typical of undisturbed bog,” Andersen says, “on balance, they’re taking up more carbon than they release.” Now, with what she’s learned from Talaheel and other restoration sites, she believes that peatlands damaged by plantations can be transformed from carbon source to sink in fewer than 10 years.

As she nimbly picks her way back across the recovering landscape, Andersen gazes at the mottled emerald and olive of the open bog. She sees hope for the ecosystem’s ability to adapt. “Peatlands have been around for such a long time, slowly but surely forming peat,” she says. “That suggests they’re intrinsically very resilient.” If they can be restored to health, she and other scientists believe that peatlands will endure, even in a time of unprecedented change. Holding its secrets close, the bog hides a paradise for birds and beetles—and, deeper down, a vast stockpile of carbon we can’t afford to set free.

Peter Cairns

Peter Cairns is a conservation photographer and filmmaker with more than 20 years of professional experience. A long-time advocate for rewilding and nature-based tourism, Cairns is a co-founder of SCOTLAND: The Big Picture, a serving Board Member of the Scottish charity Trees for Lifeand is a Senior Fellow of the International League of Conservation Photographers.

Sharon Levy

Sharon Levy is a science journalist and wetland enthusiast based in Northern California. She’s the author of The Marsh Builders: The Fight for Clean Water, Wetlands and Wildlife, from Oxford University Press. Her work has also appeared in Undark, BioScience, Nature, New Scientist, and other magazines.

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