Know-How Exchange : SEO/SEM

You might start by buying Google Adwords, creating a blog that folks who are into chicken coops might find interesting, and generally establishing a presence on social media.

Is there a trade journal that deals with this topic? If so, you can advertise there and/or create some interesting articles for them that would at least mention your forum.

From an SEO perspective, identify likely keyword searches for potential forum members using tools like Google Adwords Keyword tool. Once you understand how people search, that'll help to craft your home page for your forum. The next logical step would be to try to boost your ranking by getting backlinks from various related and reputable sources.

Your forum (whether it be paid or not) needs a strong reason for people to stick around. That means you need a critical mass of information and active people present before the traffic arrives.

Finally, as Michael suggests, social media makes good sense.

You could do this, but really, get on Facebook and Twitter. Search for people on both who are into... coops... and talking about them. Then invite them to your forum.