Everytime you create a new thread, by default the Forum sets the thread viewing to watching. To stop getting these notifications, see the button at the bottom of each thread that says "Watching", click it, and you have the choice of tracking, normal, or off. Either of those three will either reduce or not have any notifications.
You'll need to go into your preference settings if you want to turn email nofifications off as well, easy enough to do, as well a few other settings in there that you can customise to your needs.
I always have to make sure I take watching mode off everytime I make a new thread, otherwise endless notifications of people posting in a thread would do my head in