What is it?
Some of our forums are auto-pruned i.e. topics are deleted a specified number of day after they have been posted to.
Note that auto-pruning works differently in the Wiki forum: REPLIES to topics are pruned but the opening post i.e. the wiki article is not pruned. The idea here is that members may make suggestions for improvements to the articles. Wiki articles themselves may be manually removed by Wiki moderators.
Why do we do it?
Because TerraGeneis has been around since 1997 and although the current forum is more recent (it went live in 2006) the fact is that we would have a significantly larger number of topics if we didn't clear them out.
Topics, and the images associate with them, use up space on the server. Storage space costs money.
Additionally: the more topics we have, the more data our system has to look though in order to display something.
It's just not practical to keep old topics especially as we fully intend that TG will still be around in 10, 20, or even 100 years from now.