Hi there!
As far as I can trace it, the story's about the local situation amongst the period of Cromwell.
Portmore castle was erected in 1664 en broken down only 7 years later.
The oak forest was used for warfare (warships)

The catholics in the northern parts were divided in two groups; the original irish population and the lords of old england.

Since the last group stood closer to the english crown, the were offered to get some of the occupied land back. In return they had to brake down Portmore castle and the oak forest (that "price" was their "purchase") The huge oak at the shoreside of the lake is the ornament tree.

Looking at the lyrics, it seems to me that the words must have been coming from the original (northern) irish population from that time, or from the owner of Portmore castle.
On one of the many websites I visited, there was written that there are still some remains of Portmore castle at the original buildingsite

I will use the song, performed by the band "Gregorian" (plse find it at youtube, it's really beautifull) in a theaterperformance about worldpeace, somewhere next year.
As a foreigner to England, Scotland and Ireland, I can only feel sorry for all those who died or suffered any other way, in this battle between religions, that lasted upto the late nineteen-nineties.
Nowadays, not only in Ireland, Scotland and England, but all over the world,unvoluntarely we are confronted with warlike activities in the name of religion. Why, oh why do we want to rule and conquer over others? Why can't we accept differences and live peacefully next to eachother?..........