(Image: Erland Grøtberg/Gett)
A team went looking for bogs that bear witness to Britain’s great deforestation – but most were too young. What’s the path out of the quagmire?
WINNIE-THE-POOH’S friend Eeyore lived in a corner of the English countryside that will be familiar to anyone who has ever been walking in this part of the world. You decide to take a shortcut. The ground begins to get slightly soggy. Then very soggy. But you are a hardy hiker, and surely it’s not worth turning ba… squelch. One boot sinks deep enough to take on a sockful of slime. You may let out an Eeyoreish sigh.
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But for some, the small bogs that dot the British countryside and many other damp landscapes are places to be sought out, not avoided. We’re not just talking about wildlife, although wetlands are havens for rare plants and animals. For scientists, bogs are a treasure trove of information. They preserve pollen and spores that open a window to the past going back many thousands of years.
Tony Brown is one of the researchers trying to open this window. A few years ago, his team began to search out bogs to take core samples from. It was a job that involved getting wet and muddy. And that wasn’t the only problem.
Brown wanted to study the great transition in the landscape that took place when forests were felled to make way for farmland. This process began about 5000 years ago, but it really got under way during the Bronze Age, which in Britain was from about 4500 to 2500 years ago. So the team wanted to find bogs that went back this far. But at site after site, the peat went back almost, but not quite, far enough to record the transition. “We were frustrated,” Brown says. And at first they were baffled, too.
“The team wanted to find ancient bogs. But at every site, the peat only went back to the Bronze Age”
Peat bogs form where the soil becomes permanently sodden, encouraging the growth of plants such as sphagnum moss. The low-oxygen, acidic conditions preserve organic material, from dead plants to wind-blown pollen and spores to the occasional ancient murder victim. Carbon dating layers and identifying the pollen and spores reveals what the vegetation was like in the past, and thus what the climate and people were up to.
Large peat bogs form in the bottom of broad valleys and on upland plateaus kept wet by heavy rainfall. Such bogs often date back 10,000 years to the end of the last ice age. But to get a better picture, Brown’s team also sought out smaller bogs, often covering no more than 1 or 2 hectares.
These miniature mires typically form in smaller valleys where groundwater seeps down from the slopes and, in the case of spring mires, where a stream emerges. And it was these smaller mires that only provided a record going back 2000 or 3000 years. The question was: why?
“Whenever I give a talk on this, people say, ‘How about beavers?’,” says Brown, who is a geographer at the University of Southampton, UK. Old beaver-dammed lakes can indeed turn into bogs, and beaver numbers were probably falling at this time because of hunting. But the mires that Brown and his team were studying are too small and on ground that is too steep for them to have been made by beavers.
As the team puzzled over the findings, Brown remembered an idea aired in the 1970s by Peter Moore, a botanist at King’s College London. Moore had been studying small mires dotted about the heathland of Surrey in southern England. He suggested that deforestation generated these mires. When trees were removed, they were no longer there to suck up lots of moisture, so the ground became waterlogged.
Moore’s idea was dismissed in the 1980s, when the role of climate change became more prominent. During the Bronze Age, the British climate got wetter, and this alone seemed enough to explain the increased bogginess in some areas. Researchers also pointed out that some bogs predated the axe-wielding farmers. But a few counterexamples do not disprove the idea, says Brown. After all, deforestation does not have to account for every mire.
So last year his group put together a computer model to see whether Moore’s idea really holds water. They coded in the local topography of a bog called Hoar Oak in south-west England, along with the known ability of trees to suck up and sweat out water. The result was convincing, at least in this case: “When you reduce evapotranspiration you get saturated soil,” says Brown.
So it looks as if many of these small mires are artificial, the product of ancient meddling by people. After all the effort of clearing the land, the would-be farmers may have had only a few harvests before it turned boggy. But their efforts may not have been entirely wasted. Some of these small mires seem to have been desirable property during historical times, perhaps because they provided oases of lush grazing during droughts. In the New Forest in southern England, for example, is a mire enclosed by a bank known as the Bishop’s Dyke, said in local legend to be the area that the Bishop of Winchester could crawl around on his hands and knees in a day.
Blooming boggy
Brown’s findings, presented at last year, fit in neatly with what we know about the history of farming in Britain. The first farmers felled and ploughed using tools of flint. Evidence is emerging that they weren’t very good at it. “Farming started in a piecemeal way in isolated areas, then almost disappeared, and only picked up properly in the early Bronze Age,” says Brown. It may be that the first wave of farmers brought methods that were ill-suited to the region. Only later was the land transformed by the cutting edges of Bronze Age technology.
“It is certainly plausible,” says Iain Diack, a wetland specialist at the conservation organisation Natural England, based in Telford. “One can imagine that these places did receive a lot more water once the trees were removed, although one imagines there was some kind of wetland before, but not perhaps as wet.”
And Brown and his colleagues are not the only ones to conclude that many bogs were made by our ancestors. In the past three years, teams about the small mires of the Massif Central in France and the western coast of Norway.
Brown would also like more data on the bigger bogs of England. Even though these mainly formed much earlier, their extent may have been boosted by deforestation. “I suspect if we had enough on dates of blanket peats, we would find a big acceleration in the Bronze Age,” says Brown. But early farmers also destroyed many wetlands by digging drainage channels, as Diack points out, so it is not clear whether the country as a whole got boggier.
Now there are to the way they were before the Bronze Age, by planting new woodland to lock up carbon dioxide and reduce the risk of flooding.
But if Brown is right, then some of these tree schemes could dry up our spring mires. And that’s not good. “They support an unusual assemblage of plants and animals, unmatched in western Europe for diversity,” says Diack. (Any enmired hiker should look out for the marsh fritillary butterfly and the bog orchid.)
So some places should not be reforested, or should be reforestated only if old drainage systems are removed at the some time. With care, we should be able to maintain the rather boggy and sad places that grace the English countryside. Good news for dragonflies and marsh gentian, melancholy donkeys and the British sock industry.
This article appeared in print under the headline “Enmired”
