301 redirect using .htaccess
Since the RewriteBase directive applies to the entire .htaccess file, it should not be buried between two RewriteRules.

You don't need capturing parentheses for the RewriteCond.

Options +FollowSymLinks

RewriteEngine on
RewriteBase /

RewriteCond %{HTTP_HOST} ^example.com [NC]
RewriteRule .* http://www.example.com/$0 [R=301,L]

RewriteRule ^locations\.php$ compare-biomass.php [R=301]