Hi Peter,
The community dashboard you see is actually a course page. The links to forums on this page are contained in a formatted HTML table and the forum links go off to orphaned forum activities.
If you want to use a dashboard, you could link off to a forum activity hosted on a course page. Just make sure that users will be enrolled in the course page. It would also be a good idea to include a link back to the dashboard from within the forum activity.
The main advantage to using a course page, rather than a dashboard is that you can add the search forums block. You can also use activity restriction settings to limit forum activities to certain audiences.