You can disable them if you want with something like Ghostery for Firefox. Or use an anonymous private browsing tab/session.
Some track your login and views so the forums display correctly. Some track which ads have been displayed. Some are traffic analysis. Sometimes the ad services bundle trackers into their ads for their own statistics and verification.
Ghostery will explain most of them.
Remember, your use of this site is free, yet it is far from free to operate. The trackers aid in monetizing the site to keep it up and running for your use.
Ghostery only reports 7 so I don't know where your extra are coming from. Perhaps you have some extra trackers from add-ons and toolbars of your own installation?