On September 2, 2003, at 0545 Pacific daylight time, a Mooney M20K, N252AK, collided with trees shortly after takeoff from Gnoss Field Airport (DVO), Novato, California. The airplane was operated by the pilot/owner under the provisions of 14 CFR Part 91, and sustained substantial damage. The private pilot, the sole occupant, was not injured. Instrument meteorological conditions prevailed for the local area flight that was scheduled to terminate at Oakland International Airport (OAK), Oakland, California. An instrument flight rules (IFR) flight plan had been filed, but had not been activated. The pilot was interviewed by the Safety Board Investigator-in-Charge. The pilot stated he had received a weather briefing from a direct user access terminal (DUAT) service and there was no significant weather for the flight from Novato to Oakland. He reported the flight was to take place in the early morning, 0545, so it was dark outside. On the takeoff roll out, some jackrabbits passed in front of the airplane. The pilot stated that the rotation was normal, but he forgot to retract the landing gear. While he was trying to figure out why the airplane would not climb, it impacted trees off the departure end of the runway. The pilot was interviewed by a Federal Aviation Administration (FAA) inspector. The pilot stated that he filed an IFR flight plan, but decided to depart using visual flight rules (VFR). The weather report he received indicated clear weather along the route, and the sky was clear at DVO with visibilities greater than three miles. During the takeoff roll jackrabbits ran across the runway and caused a minor distraction. The pilot reported that after rotation there were no ground lights, and no visible horizon. At that point he engaged the autopilot. After he engaged the autopilot, he noted that the airplane was not climbing as expected. Before he was able to determine what the problem was the stall warning activated. He disengaged the autopilot and attempted to lower the nose. The pilot reported that the airplane then entered the trees. He also noted his airspeed approached 95 knots. Numerous attempts to obtain a written statement from the pilot were unsuccessful. According to the United States Naval Observatory sunrise for the date of the accident was at 0541. Weather obtained from the Federal Aviation Administration for the DVO area at the time of the accident was reported as 1/8-mile visibility and overcast clouds at 100 feet. Napa, California, elevation 35 feet mean sea level (msl), is located about 060 degrees at 14 nautical miles from the accident location. At 0454, reported weather conditions were: winds from 230 degrees at 4 knots; visibility 8 miles; a broken cloud layer at 500 feet; temperature 53 degrees Fahrenheit; dew point 53 degrees Fahrenheit; and altimeter setting 29.88 inches Hg. At 0554, the weather was reported as calm winds; visibility 7 miles; a scattered cloud layer at 500 feet; temperature 53 degrees Fahrenheit; dew point 51 degrees Fahrenheit; and altimeter setting 29.89 inches Hg. The airplane was inspected at Plain Parts in Pleasant Grove, California on November 3, 2003. No discrepancies were noted with the airframe or engine. PERSONNEL INFORMATION A review of Federal Aviation Administration (FAA) airman records revealed the pilot held a private pilot certificate with a rating for instrument airplane. The private pilot certificate, with the airplane single-engine land rating, was issued on January 27, 1997. The pilot held a third-class medical certificate that was issued on August 13, 2003. It had the limitation that the pilot must have available glasses for near vision. ADDITIONAL INFORMATION The airplane was released to the owner's representative on December 18, 2003.