When the Burren was forest
Fossil fungal spores recovered from local turf are helping piece together the complex history of how human activity made the Burren what it is today, writes DICK AHLSTROM.
THE RUGGED BURREN landscape of north Co Clare was once covered in pine trees and hazels before being cleared and later grazed flat by early farming activity, according to new research. A clearer picture of the impact of human activity and farming on the Burren over the last 3,500 years has emerged as a result, with the team from NUI Galway relying on an unusual information source – the spores of a fungus that grows on cattle and sheep dung.
The presence of the spores and tree pollen in peat samples recovered from a number of locations across parts of north Clare has helped to explain the current state of this ecologically important landscape, explains Prof Michael O’Connell.
Based in the palaeoenvironmental research unit of NUI Galway’s School of Natural Sciences-Botany, he and German PhD research fellow Dr Ingo Fesser went in search of coprophilous fungal spores.
The spores recovered from peat samples up to half a metre deep is a sure sign that cattle and sheep once grazed nearby, O’Connell explains. They are an ideal marker of grazing for two reasons, first because the fungi only grows on dung and second because the resultant spores remain close to the ground and do not spread widely.
“We were trying to look at the long-term environmental changes that have taken place in the uplands,” he says. In particular they looked at the stretch west of Ballyvaughan between Cappanawalla Hill and Black Head.
Today it is a stark landscape, bare limestone riven by channels where arctic-alpine species that make the Burren world famous including the mountain avens, bearberry, crowberry and the beautiful gentian cling precariously to life.
It was not always so, O’Connell indicates. “We dug out peat sods and the peat has preserved these fungal spores.” Pollen too is trapped in the peat, giving an indication of the original plant cover and evidence of later farming activity based on the presence of the spores.
The data stretches back about 3,500 years, with peat an ideal medium for providing information about time. “We know the date because we have radiocarbon-dated it,” he says. “We have built up the record [of farming activity] from the mid-Bronze Age.”
The Burren would have looked quite different all those years ago, he said. “The present day appearance of the Burren is not representative of what the Burren looked like in the post-glacial period.”
THE LONG-HELD assumption was that the terrain was scraped clean by the glaciers, leaving space for the arctic-alpine plants to take hold, but the fossil record shows that pine and hazel covered the region after the glaciers left 12,000 years ago. “The Burren’s open woodland provided an environment in which the alpines could survive.”
The pine woods likely persisted until about 2,500 years ago when farming activity required the clearing of trees.
“It was not just the climate affecting the region, it was the human impact,” O’Connell said, referring to research published last week in the British Ecological Society’s Journal of Ecology.
The evidence collected by O’Connell and Feeser, who won a research fellow grant from the Irish Research Council for Science, Engineering and Technology, detailed the spread and extent of grazing activity in the region.
Added to evidence provided by other researchers, it has led O’Connell to argue that the arctic-alpine plants coexisted with the forests and then later survived the regular “mowing” by grazing livestock that cleared away scrub and tree seedlings.
Evidence for the coexistence of the pine and alpine species is readily available in similar harsh limestone environments in Scandinavia where pine forests have arctic-alpine undergrowth, he says.
The pine was cleared first but as populations rose and farming activity spread, even the persistent hazels were cleared away from the northern Burren highlands by the 17th century. “The increase of the [coprophilous] spores coincides with the complete disappearance of hazel.”
The two researchers have also raised some interesting questions about whether the Burren’s coastal uplands were always so devoid of soil. Radiocarbon dating of charcoal recovered from fissures in the limestone suggests that Neolithic and Bronze Age farming began a process of soil erosion that continued well into the 1300s, he says.