If you are using any Caching plugin then you should not cache the forums part. We use Cache Enabler, the very simple caching plugin. You can exclude forums, topics etc. of bbPress using the following regex.
bbPress
How to Increase Font Size of bbPress
Add the following code snippet in your theme style.css /* bbpress specific styling */ #bbpress-forums, #bbpress-forums ul.bbp-forums, #bbpress-forums ul.bbp-lead-topic, #bbpress-forums ul.bbp-replies, #bbpress-forums ul.bbp-search-results, #bbpress-forums ul.bbp-topics, div.bbp-template-notice li, div.bbp-template-notice p, div.bbp-breadcrumb, div.bbp-topic-tags { font-size: .9rem; line-height: 1.5; } #bbpress-forums .bbp-forum-info .bbp-forum-content, #bbpress-forums p.bbp-topic-meta, span.bbp-admin-links a { font-size: .9rem; }
bbPress Styling Guide for Genesis theme
Copy /wp-content/plugins/bbpress/templates/default/css/bbpress.css to /wp-content/themes/yourtheme/css/bbpress.css and edit the copied file accordingly.