your great-grandmother's tree cannot be copyrighted though if the poster included your own comments then these may have given you a legal basis for a take down. The rootsweb pages often include detailed and legally accurate help on what is and what is not copyright (possibly also ancestry.com may have similar guidance - most people assume too much is copyrightable, no genealogical details are, as all are in the public domain) - there is no such thing as 'strong copyright' nor is it necessary to include a (c) symbol on any work for it to be copyright - copyright is acquired automatically though adding the symbol (which is a hangover from old legislation) does indicate that you are probably willing to defend any copyright.