There are two ways to track who has added or edited calendar events. Login as administrator and go to:

Admin Menu > under Calendar Settings > Calendar Options > Expert Options Tab > Event Change Tracking

• Enter email address(es) to the "email address to receive change notices" field to set up automatic email notifications of event additions, deletions, and edits > Save
   
• Optionally, check the box "Show user who last updated..." > Save 
  The user who added or last updated the event will appear at the bottom of all event popup descriptions.