No. The Gamma Forest was created for "A Good Man Goes to War".
the Doctor hasn't visited the Gamma Forest. He clearly had no idea who Lorna Bucket was. At some point after "A Good Man Goes to War", the Doctor will go to the forest and bump into a younger Lorna.
There's no guarantee that his visit to the Gamma Forest will ever actually be shown in an episode. For all we currently know, it could have been one of the things he did between the end of "The God Complex" & the start of "Closing Time". None of that was shown but it occupied about 2 centuries of the Doctor's timeline. Of course, we don't know, either, that his visit to the Gamma Forest won't be shown. We just need to wait and see what happens.
There was a short story illustrated by Lee Sullivan in The Official Doctor Who Annual 2013 called Lorna's Escape which told the story of a girl and her friend from the Gamma Forest and their mysterious savior who stopped a dangerous creature from terrorizing them.