The powered parachute was an existing aircraft without an airworthiness that was certified as an experimental light sport aircraft, The pilot was attempting a takeoff towards the northeast from a grass field in a park, which had trees at its edge. The aircraft was about 20 feet above ground level when the parachute contacted the trees, which was about 644 feet from the start of the takeoff roll. The grass length in the field was approximately 2 1/2 inches. The prevailing winds were calm and the density altitude was approximately 2,800 feet. The aircraft sustained substantial damage, which included bent fuselage tubing. The pilot and passenger received serious injuries. Examination of the aircraft did not reveal any anomalies that would have precluded normal operation. The parachute was a Performance Designs Paraglider, Inc. Sunriser, part number PG0500P01, serial number PG500-001713., manufactured 08/1999. Weight and balance information for the aircraft shows a useful load of 540 lbs. The following weights were recorded: pilot - 195 lbs, passenger - 215 lbs, fuel - 60 lbs, 1 gallon of coolant - 8 lbs, 4 pints of oil - 4 lbs, 2 helmets - 4 lbs. The only takeoff performance information for the aircraft lists a takeoff roll of 25 feet to 300 feet. There is no aircraft performance data, which is not required by certification regulations, available to the pilot.