Ancient Animal Dung Helps Botanists Unearth Burren's History
Thursday, 23 July 2009
Botanists from NUI Galway have used a most unlikely source – fungi that grow on cattle and sheep dung – to shed new light on farming and its impact on the Burren, County Clare, the best developed karstic region of western Europe. Using old and new techniques, including analysis of fossil spores produced by fungi that grow only on herbivorous animals' dung, the study – published in the British Ecological Society's Journal of Ecology – shows how farming waxed and waned over the past 3500 years and how this shaped Burren's extraordinary plant life. Dr Ingo Feeser and Professor Michael O'Connell from the NUI Galway collected peat and soil samples from upland areas of the Burren. It is well known that peat, because it preserves pollen, archives long records of past plant life. But scientists have only recently realised that peat also preserves other fossils such as fungal spores. By using both these techniques and radiocarbon dating, Feeser and O'Connell have uncovered the history of upland farming in the Burren and the major role that cattle and sheep grazing has played in shaping the area s flora and landscape. According to Professor O'Connell: "Spores from fungi that grow on dung of cattle and sheep are really useful for two reasons: they preserve well and, since they are produced at ground level they stay put. That means when we find them as fossils, we can be sure that grazers were present at the sampling site all those years ago. Together with fossil pollen, they help us distinguish between the impact of factors such as climate change and upland grazing on species composition and biodiversity." The fossil pollen reveals that pinewoods once grew on the exposed north-western Burren hills that face the Atlantic Ocean on the southern side of Galway Bay until around 500 BC, when increased farming by Iron Age peoples resulted in pine no longer being the dominant tree. "Present-day open pinewoods on limestone soils in Scandinavia, with a ground flora that includes many typical 'Burren' species, are the closest analogy to these former pinewoods on the coastal Burren uplands," says O Connell. This means it is no longer necessary to invoke special conditions, such as persistence of open, treeless conditions since the retreat of the ice sheets, to explain the presence of arctic-alpine species in the Burren; rather these plants found favourable conditions, and thus survived, within open pinewoods. The study also emphasises the highly dynamic nature of the relationship between humans and nature in the Burren since farmers first arrived about 6000 years ago. While open pinewoods dominated coastal uplands, hazel scrub was important in inland areas such as Corkscrew Hill where farming impact was higher. Hazel was also highly dynamic and sensitive to farming pressures. When farming declined at the end of the Iron Age (about AD 300), hazel replaced grasslands in what the researchers refer to as the 'Late Iron Age Lull'. The reverse occurred in the late eighteenth/early nineteenth century when population levels rose dramatically and the Burren became so bare that the woody stems of the mountain avens (Dryas) were used as a substitute for wood. This, in turn, contrasts with the present-day situation when farming is on the decline and the spread of hazel reduces the habitat available to the typical Burren flora and hides the rich archaeology of the region. However, vegetation and farming are not the only dynamic features of the Burren. The placename 'Burren' denotes a rocky place that aptly describes this extensive area of bare limestone rock. "That the Burren landscape always had this lunar-like appearance is not true," says Professor O'Connell. By radiocarbon dating charcoal contained in eroded soils recovered from grykes (deep fissures in the limestone), the NUI Galway researchers have shown that substantial loss of soil through erosion followed not only the clearing of primeval woodlands by the early farmers, i.e. the megalith tomb builders, but continued to be a feature of the Burren until well into medieval times. Ingo Feeser and Michael O Connell (2009). Fresh insights into long-term changes in flora, vegetation, land use and soil erosion in the karstic environment of the Burren, western Ireland, Journal of Ecology, doi: 10.1111/j.1365-2745.2009.01533.x, is published online on 22 July 2009.