I agree w/Resin, looks like it could be a red maple (based on colour) but that's just a guess. If you do visit again, get a close-up of the foliage (even if all the leaves have fallen) so we can see the shape. Also a close-up of the branches to show the leaf arrangement and buds would be very helpful.
I, too, would have thought it's from the Maple family. Wish my plant I.D. skills were better, especially for trees. By the way, Mt. Usher garden in one of my very favorites places in Ireland. The first picture book I received of Ireland had the most gorgeous photo of a scene there--it looked like I pictured the Garden of Eden would have looked. I had to see it for myself, hence our first trip to Ireland. I took many photos of that lovely spot.
I am thinking maple also, and red maple is a good match. If it was here in the U.S. I would be more likely to think red maple, but since you are from Ireland I don't know what types of maples or other trees grow around there.
From what I can see in the photo the branch structure and leaves make me think maple but from that distance it is hard to tell.
Many types of maples can have the orangish color of the one in your photo.
I work with a lot of maples in bonsai (they are one of my favorites) and maples generally have that powerful branch structure with a lot of slight bends in the trunk like in your picture.