I have http://hollywoodnose.com as a main site. Then I have http://forum.hollywoodnose.com as the subdomain. I'm cautious to link to the subdomain from the main site. I did this before and droped 50% of traffic from the main site.  Also, Google Webmaster Tools showed over 3000 incoming links from Hollywood Nose to the subdomain / forum.  I'm assuming Google frowned on this and saw it as spam or something of that nature. All I would want is link to the subdomain in the top nav bar of the main site. Is this safe? Will I get an overabundance of incoming links resulting in an SEO drop? Does anyone have any experience in this matter? Thank you.
SEO effects of linking to subdomain
seo;subdomain;links
Subdomains are seen as part of the same website as domain.com so this won't have any effect on your SEO.