bbPress.org

1. remove /register.php or redirect it to somewhere, or replace it with your page (tell visitors your forum temporarily doesn’t accept new registrations) then you can skip step 2.

2. remove register link from your login-form.php in you template folder.

3. Use this. You may need these

$roles['member']['capabilities'] = array('read' => true);

$roles['moderator']['capabilities'] = array('read' => true);

$roles['administrator']['capabilities'] = array('read' => true);