How to change forum 'display options'

[mp3u]

How do I set the default display options for each of the forums to be 'from the last year' rather than 'last month'. Some of my forums are always busy and up to date but there are certain areas of the site where posts are less frequent. Inexperienced users could easily miss the box at the bottom of the page and assume that there are only say 5 posts in that entire section of the forum that could have 500...