What you will need to do is to put an exception in your .htaccess for /forum so it doesn't get rewritten. Something like this:

    #Checks to see if the user is attempting to access a valid file,
    #such as an image or css document, if this isn't true it sends the
    #request to index.php
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    #This last condition enables access to the images and css folders, and the robots.txt file
    #Submitted by Michael Radlmaier (mradlmaier)
    RewriteCond $1 !^(index\.php|images|forum|robots\.txt|css)
    RewriteRule ^(.*)$ index.php/$1 [L]

Just remember you can't have a forum route in Laravel.