Quote Originally Posted by Black Mage
Ymir, Treant's/Torent Forest, and Heimdall are the same throughout both Tales of Phantasia and Symphonia.
Just to add to that, the one thing that made me laugh the MOST out of Symphonia was when Colette, while entering the Treant's Forest states how beautiful it is and how she hopes that in the future everyone can travel there and see it.

Ironically, in ToP it's identical to the way it is in ToS, only those the elves allow can enter the Treant's Forest, and only with a Writ from the king can they enter the Ymir Forest in the first place.

Oh and also you need the Eternal Sword to reveal Dhaos' castle just like you do Derris-Kharlan/Welgaia, and there's a panel in Welgaia that sends your party away just like in Dhaos' castle, though in ToP you were just sent to a lower level and a prison when in ToS each of the characters were sent of to their "The *whatever*" boss thingies.