Indigenous oak, elm, birch and ash forests are no longer under threat from development but from the intrusion of species such as sycamore and beech, which migrated to the country in the middle ages.
James Martin, an environmental consultant who co-ordinated the National Parks and Wildlife Service survey of native woodland in Ireland, said: “The most surprising finding was the prevalence of these non-native species and the fact that they are now the major factor in native woodland reduction. Most people, I suspect, would consider the beech and sycamore as part of the traditional Irish landscape but they are actually more recent. In natural habitat terms, they are invaders.”
He said the “new” trees spread was a cause of concern “These species seem to reduce biodiversity in the sites, in both animal and plant life and thereby reduce distinctly Irish habitats,” he said.
Though sycamore and beech trees are well adapted to an Irish climate, they do not form part of the country’s historical natural fauna. This is because they failed to colonise before the glacial age and the formation of the Irish Sea, which provided a barrier to invaders.
The survey measured tree cover in wooded areas of greater than one hectare using satellite photography. It covered the 26 counties and was carried out at the same time as a survey of Northern Ireland.
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“There is no definite cut-off point, but generally if more than 25% of non-native trees make up the canopy then the site is classified as non-native,” said Martin. “The survey found that 75% of wood classified as native had a sizeable amount of non-native species, while only 5% of sites were totally clear of intrusion.”
Exact figures on the percentage of wooded land cover in Ireland vary both because of the lack of previous exhaustive surveying, as completed in the native woodland survey, and the dynamic nature of the habitat with commercial forestry and planting schemes. However, estimates are that between 7% and 9% of Ireland is afforested, 1% of this being native and most other woodland being commercial plantations of exotic coniferous trees.
Forestry bodies and the Department of the Environment estimated in the 1990s that approximately 1.5% of the Irish land surface comprised native woodland. These now appear to have been overly optimistic.
Although a further 7% of Ireland is covered in commercial woodland, the country still has the lowest afforested area of any European country other than Iceland.
The survey found most native woodlands were confined to the southwest counties of Cork, Kerry and Clare. These account for some 22,570 hectares of native woodland, or approximately 25% of the total in the state. On the east coast, the only large concentration of native woodland is to be found in county Wicklow, which has 4,684 hectares.
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The survey will be presented at the country’s first major conference on native woodland to be held at the Galway and Mayo institute of technology between September 8-11. Dr Sasha van der Sleesen, of Sylvan Consulting Ecologists, who is helping organise the conference said: “Old sessile oak woods with holly and yew woods, both largely based in the Killarney area, are both important native woodland types on a European level that occur in Ireland. The survey found that these were also experiencing native intrusion.
The percentage of native woodland increased as the 20th century progressed and demand for use of native wood for fuel and building lessened. The post-independence government also set up reforestation programmes in the hope of developing the natural resource.