Originally posted by jthibeault:

After I posted this I realized that campfires don't prevent the summons, so I guess wards wouldn't be any different.

They dont prevent summons, but continuously damage the elder by burning him. Just switch side when he summons roots,they are only on small area. Personally,i just shot him with fire arrows and circled around the pillars. Easiest boss as you can shoot but he cant hit you with his ranged attack.