Members are free to edit and delete their own posts so I suppose to that extent you have ownership. The only time you wouldn't have access to one of your posts is if the topic has been locked. In this instance you would need to contact us so that we could reopen it for your edit. No problem.
If you're talking about posting "stories, poems, song lyrics etc" you would retain ownership to those exclusively if you claim them as yours.
This is the internet and "ownership" laws are never clear.