The pilot reported that the purpose of the flight was to relocate Christmas trees to a nearby drop site. He had completed several loads over a duration of about 15 minutes. He said that as he was maneuvering the helicopter to the drop site with another load, the helicopter began to settle with power. In reaction he applied more collective in an effort to arrest the descent. The helicopter continued to descend and he attempted to reduce the collective and maneuver forward. The helicopter touched down hard on the heels of the skids and the helicopter's nose came to rest in a pile of Christmas trees. The tailboom was bent as a result of the hard landing. The pilot stated that there were no preimpact mechanical malfunctions or failures with the airframe or engine. The Rotorcraft Flying Handbook, FAA-H-8083-21, Chapter 11, Helicopter Emergencies, Vortex Ring State (Settling With Power), states: "The following combination of conditions are likely to cause settling in a vortex ring state: 1. A vertical or nearly vertical descent of at least 300 feet per minute. (Actual critical rate depends on the gross weight, r.p.m, density altitude, and other pertinent factors.) 2. The rotor system must be using some of the available engine power (from 20 to 100 percent). 3. The horizontal velocity must be slower than effective translational lift." It adds that "When recovering from a settling with power condition, the tendency on the part of the pilot is to first try to stop the descent by increasing collective pitch. However, this only results in increasing the stalled area of the rotor, thus increasing the rate of descent. Since inboard portions of the blades are stalled, cyclic control is limited. Recovery is accomplished by increasing forward speed, and/or partially lowering collective pitch. In a fully developed vortex ring state, the only recovery may be to enter autorotation to break the vortex ring state. When cyclic authority is regained, you can then increase forward airspeed."