Erik Roner

Several witnesses risked their own lives trying to rescue MTV star Erik Roner after he crashed into a tree during a skydiving accident last week ... attempting to scale a 30 foot tree in an effort to treat the injured man ... TMZ Sports has learned. We obtained the 911 calls made by several…

Action sports star Erik Roner -- one of the stars of MTV's "Nitro Circus" -- died in a freak skydiving accident in Lake Tahoe, California ... this according to the resort where it happened. A spokesperson for Squaw Valley Ski Resort confirms Roner was performing a jump with a group of skydivers as…