PAP2012 said:native soil may have some or all the things a plant will need at least to start out with but shouldn't amendments to full fill that gap be added?
I feel the same way.
As I only plant organically, If I'm planting a solitary tree instead of an entire island, I top-dress the entire planting circle with compost/manure before covering with mulch.
I find that I get much faster growth when I work up a large area with a number of trees, compared with setting out a specimen tree in the middle of a patch of turf.
You've asked some good questions, and I think that the best answers will only be arrived at by getting out there and planting some trees, and then observing how well your babies grow.
