Have you ever watched videos where a tail rotor hits something (sudden stoppage)? The rotational velocity that builds is pretty serious (and that's without a pilot pulling all remaining collective at the time). We're not talking about LTE/LT-Thurst where the tail rotor slowly becomes less effective due to wind/drive-shaft shear where the T/R is still spinning for a few seconds and a slow yaw then turns into a fast yaw. Think: tail rotor destroys itself followed by the tail boom collapsing. Now consider that when the tail rotor hits the trees...
Back when I was an IP, I really emphasized doing as most RFMs (that have the EP (sorry Airbus guys)) states for "Landing in Trees" ensuring you got back to ZERO airspeed (with a good terrain flight decel; I know civilian guys may not practice that because the "quick stop" is actually fairly different, but basically ensuring you come to a complete stop while pivoting around the axis of the tail rotor) while still a few (and only a few) feet above the trees, then pull all remaining collective as if doing a hovering auto right there. Then, as you go down (with zero airspeed and no more collective to pull), all G-forces are in the z-axis which the body can actually handle.
If you can do this over pines instead of hard-woods (and trees of the lowest height), the softer wood will splinter and bend as you enter, cushioning the fall (and I know that's VERY relative). If you go into hard-woods, I always felt a single strong limb could tilt the helicopter any certain direction during the fall, then you risk being out of that z-axis or a risking a different limb then entering the windshield/windows during the fall and that injuring you (since hard-woods typically grow taller, you'll be falling through the trees for a much higher height (unless you're in California/Oregon/Washington)). Look at the pictures of varying aircraft that have crashed in different types of forrest to see what I mean.
If you allow the aircraft to fall down in a nose high attitude you risk being out of that z-axis (straight up and down) and then when the tail rotor hits, the helicopter will yank to the right (x/y-axis which aeromedical science shows is the worst angle for the human body to handle) making surviving the accident sequence much less possible.
Granted, this all assumes you're SkyKing during the auto and that my theory is correct.
That dude had some skills to pull off doing an auto with a 180 turn at the very bottom before going into the trees, though. Pretty awesome.