This is the tree which yields the edible chestnut, as opposed to the unrelated horse chestnut (Aesculus hippocastanum). It is not a native but has been grown in Ireland for many centuries. The tree is also sometimes called the Spanish chestnut, a reference to the fact that Spain is one of the older sources of imported 'nuts' (seeds).
Probably all the trees in Northern Ireland are planted individuals; most are found in demesne woodland. There is no evidence of this species producing self-sown trees in the region.
All names: Castanea sativa Miller; Castanea castanea (L.) Karst.
NBN Atlas mapping: Species account : NBN Atlas UK Species Observations database
iNaturalist: Species account : iNaturalist World Species Observations database