If you go to settings and check the forum reading options, you likely have the portrait lock on. To get to settings, tap the more button at the bottom right of the screen in the app.
<img src="http://www.ipadforums.net/attachment.php?attachmentid=35106"/>
<img src="http://www.ipadforums.net/attachment.php?attachmentid=35107"/>
<img src="http://www.ipadforums.net/attachment.php?attachmentid=35108"/>
<img src="http://www.ipadforums.net/attachment.php?attachmentid=35105"/>Turn it off and the forum will rotate from portrait to landscape.