forest shooting?

Shooting a bow and arrow anywhere in Ireland is in itself legal so long as its done safely with proper risk assessment as, if something happens, you wont be in trouble for shooting arrows, you'd be done for the fact that that arrow caused harm or damage.

Council bylaws prohibit it in public park land: for example SDCC bylaw prohibits:
Bring into a Park any air-gun, catapult or any other weapon save with the prior permission of the Council for an approved competition or for practice for an approved competition and subject to the terms and conditions of such permission.

Private land without permission is trespassing. You could also be done for hunting which is illegal. yes, you have a target and you weren't hunting, but good luck arguing that point.

Private land either owned by yourself or with permission is ok as long as its done safely. Unless you have exclusive use and it would be virtually impossible for anyone to walk across where you are shooting, it would be crazy to do it. ive seen people trying to walk in front of a large group of archers at an archery event, I'd shudder to think what would happen in a less obvious scenario.