The topic prunning control panel allows the administrator to remove topics that are older then a certain date.
Topics that are older then this number of days, weeks, months or years as specified by the 'Time Period' option, will be pruned.
Allows the administrator to specify a specific forum or category which to prune or whether to prune all forums.
Once you click on the prune button the forum will calculate the number of topics that will be affected by the prunning and ask you to confirm that you indeed wish to prune that number of topics. If you confirm the process the affected topics will be removed.
It is a good idea to run the Compact Messages utility after doing topic prunning.