unless i've mis-read the replys to your post, there is one thing nobody else has mentioned yet. You mention trees as one of the limiting factors, how dense of trees, if they are dense enough to block the wind you will loose any advantge the wind gave you (you are still in effect flying even at zero ground speed) as you descend below the canopy.
you will now need a larger amount of power to compensate for the no-wind descent
this power requirement is immediate if you are to stay out of trouble and maintain your descent rate
too close to the trees can also give you a down-draft
my only advise is have your power fully developed early during the descent (if too much, it's easy to let some off) check what you have left, if you feel you would not be able to stop a no wind descent, fly away, if you have enough power left, and the approach feel stable and good, be ready when you descent below the canopy.
(of course if the canopy or trees are NOT dense enough to block all wind, save all the wind i've used here for a time when there is a wall of trees)
