Adding a forum to your website can seem like a great way to increase the amount of natural content and build traffic to your site. However the nature of a forum means they are full of duplicate content, noisy low value pages and attract very few external links.
Link equity has become a major factor over the last 12 months, if you have too many pages on your site then your link equity will be spread too thinly and your site will not reach its full potential in Google.
Aaron Wall sums this up nicely:
If you are wasting link equity getting low value noisy pages indexed then your high value pages will not rank as well as they could because you wasted link equity getting low value pages indexed. In some cases getting many noisy navigational pages indexed could put your site on a reduced crawling status (shallow crawl or less frequent crawl) that may preclude some of your higher value long tail brand specific pages from getting indexed.
Aside from building some natural links the best way to stop a forum using up too much of your valuable link equity is to stop the low value, noisy pages being indexed. My preferred method is to use the following robots.txt file for vBulletin:
To remove any noisy pages already indexed you would need to block them using robots.txt and then visit Google Webmaster Central and use the “Url Removals” tool.
Most forum packages will have unique titles and meta description tags on all the pages – if yours doesn’t then you will need to figure out how to add these. The other pitfall to watch out for is your forum software appending session id’s to the url’s – this will harm your site in the search engines.
It is hard to cover all aspects of forum SEO in a blog post so if you have any questions please ask in the comments.