Forestation research: Ireland is playing a key role in solving the mysteries of our ancient woods, a Trinity College scientist told the BA festival.
"Significant human and financial resources are involved in woodland conservation to retain or recreate primeval habitats," Dr Fraser Mitchell said. However, there is considerable scientific debate as to what those habitats were like, as there are no primeval woodlands left in Europe.
"We are particularly interested in what the forests were like 8,500 to 5,500 years ago, before the first farmers came and exploited the forests," Dr Mitchell said. To learn what a primeval forest might have been like, he analyses pollen grains that survive for thousands of years in lake sediments. By examining these grains Dr Mitchell is able to determine the type of vegetation present in the ancient forests and estimate the density of particular plant species.
"Across Europe, we see large amounts of pollen from oak and hazel trees," he said. The big question is how to interpret these data. "Lots of tree pollen could indicate a dense forest canopy. On the other hand, modern ecology suggests that oak and hazel grow best in open parkland."
The plot thickens when Dutch ecologist Frans Vera considered the relationship between large grazing animals and their habitat. "There is abundant archaeological evidence that many different grazing animals were present in European forests at the time, such as 'aurochs,' or primitive cattle, 'tarpan,' wild horses, as well as the more familiar bison and deer," Dr Mitchell explained.
These animals have a big impact on ecology today. Vera hypothesised that they had a similar effect in the past, serving to keep the woods open, so that the forests might have resembled modern day parkland. "The crux of the debate is: did the forest control the grazers, or did the grazers control the forest?" To answer this question, Dr Mitchell looked at Ireland as a natural experiment. Isolated from Britain by rising sea-levels during this period, Ireland's forests developed in the absence of large grazing animals. "When we examine the fossil record, we find only one species of grazing animal, the wild boar, present in Ireland at the time," Dr Mitchell noted. He was then able to compare the pollen records of oak and hazel trees for 21 forest sites in Europe with 15 sites in Ireland.
Analyses revealed no differences between forest development in Europe, where large grazing animals were present, and that in Ireland, where grazing animals were virtually absent.
"These results suggest that the large grazing animals are having no impact," he explained. In other words, the forests were controlling the grazers.