Ireland's Biodiversity Awareness Campaign


Species of the Month

Below is a list of our previous 'Species of the Month'

Common Yew Tree
Witches' Butter
Hen Harrier
Eurasian Otter
Harbour Porpoise
Butterfiles of Ireland
Barn Owl



Oak Tree

Oak Tree - Dair (Quercus species)

Picture of a Sessile Oak Tree

OAK TREE- Dair – Quercus species

The oak tree is a key part of Ireland’s natural and human heritage. Following the end of the last ice age (c.10,000 years ago), Ireland, at first became a country of tundra, then of grasslands and finally became cloaked in forest. Woodlands dominated by oak and elm reached their peak about 7,000 BC and were teeming with animal, bird and plant life. However, by the nineteenth and early twentieth centuries, Ireland had become an open, grassy almost treeless landscape. While climate change, invasive species, and disease contributed to this decline, human disturbance has had the most significant and prolonged impact on native Irish forests. Clearance for agricultural land use and the harvesting of timber for use as fuel wood dramatically reduced oak woodland cover. 

Irish Oak species
Growing to heights of up to 40m and with a possible lifespan of over 1,000 years, oak trees are one of the largest and longest living broadleaf tree species in Ireland. Two species of oak are found in the country, the Sessile Oak (Quercus petraea) and the Pedunculate Oak (Quercus robur). The trees are found in different soil types and can be told apart from examination of their acorn assemblage.

Sessile Oak – Quercus petraea
The Sessile oak, native to Ireland, is the most common of the two can be considered the ‘traditional Irish oak’. Sessile oaks grow in poor acidic soils and are commonly located in hilly regions. The Sessile’s acorns have no stalks, while the Pedunculate’s acorns are suspended on long stalks. It is cultivated across Europe for its fine timber which displays beautiful wood patterning and is very durable. It is therefore popular for use in flooring and for furniture making and veneers.

Irish woodlands where Sessile Oaks are dominant:
Killarney National Park, Co, Kerry
Glen of the Downs, Co. Wicklow
Glenveagh, Co. Donegal

Pedunculate Oak – Quercus robur
The Pedunculate oak favours heavy lowland soils and can withstand periods of flooding and wet soil in winter. It is less common than the Sessile Oak and is not as popular for commercial timber use. In Charleville wood, Co. Offaly the famous Pedunculate ‘King Oak’ is said to be between 400-800 years old. Four of its lower branches touch the ground, with the longest of its branches stretching 76 feet from trunk to tip.

Irish woodlands where Pedunculate Oaks are dominant:
Abbeyleix, Co. Laois
Charleville, Co. Offaly
St. John’s Wood, Co. Roscommon

Biodiversity importance
Native oak woods are important habitats for hundreds of invertebrate species and many birds and mammals. In Ireland, almost 20 species of bird and over 200 species of insect inhabit the oak. One tall oak at Brackloon, Co. Mayo, was found to have 50 kinds of lichen growing on it with 260 earthworm in one square metre of earth below it. Oakland habitats therefore provide important homelands for a variety of species and their leaves, acorns, rotting wood and sap are important components of the food chain.


Myths and folklore
The oak tree was traditionally a symbol of strength, kingship, endurance and fertility and is often considered the King of Trees. Throughout Irish history, one can find reference to the significance of the oak tree. The ‘Brehon law’, one of the earliest forms of Irish law was set up to protect the oak and the other five ‘chieften trees’. It is likely that several Celtic and Christian religious sites were located next to oak groves due to their spiritual importance. Of the 62,000 townland names in Ireland, 13,000 have reference to trees and 1,600 have some derivation of ‘dair’ the Irish word for oak. Eg. Cill Dara  (Kildare) meaning ‘Church of the Oak’ Kildare.

Oaks in the 21st C
Currently there are no truly ancient oak woods in Ireland. However, there are some magnificent “secondary” forests with understoreys of birch and holly (in the case of sessile oak) or hazel. Efforts are increasingly being made however to restore Irish broadleaf woodlands. The Coillte-managed People’s Millennium Forests Project saw 1.2 million native tress planted in designated locations throughout the country and grants are now available for the planting of native broadleafs. 


©2007 Department of the Environment, Heritage and Local Government