The pilot reported that while on final approach to the runway, the airplane was too high. He initiated a slip to lose altitude, but the airplane was still too fast and high. After landing, the airplane collided with trees at the end of the ruwnay. The pilot further reported that the accident could have been prevented by initiating a go around sooner. Two witnesses reported that the airplane landed hard more than halfway down the runway and began to porpoise. With about 800 ft of runway remaining, they heard the pilot apply full engine power. The airplane subsequently departed the runway surface and impacted trees. A post impact fire ensured which substantially damaged the airplane. The pilot reported that there were no mechanical failures or malfunctions with the airplane or engine that would have precluded normal operation.