According to the pilot, "the purpose of the flight was to test a new instrument and conduct test approaches and landings to check flying characteristics at slower approach speeds. Previous approaches at 70 miles per hour (MPH) [were] too fast. After practicing slow flight and entering a stall speed into new instrument I was cleared for a 5-mile straight in approach to runway 2. After "dragging in" for 5-miles I attained my test final approach speed of 60 mph. There was a tree in my glide path so I climbed over it but underestimated my sink rate (which was the purpose of the test flight) the right gear snagged a limb which jerked me into a right hand roll. I applied power, leveled the wings, and pointed [the] nose ahead as it hit the ground. There were no visible markings on the runway to indicate a displaced threshold. The reason for the displaced threshold is the tree. If the runway was properly marked, I am sure I would have been reminded at least a mile out or one-half out that there was a displaced threshold and avoided the incident."