Bruce,
I actually did some energy calculations. A mixed apple (10%)-hazel (15%)-chestnut(25%)- walnut (15%)-pecan(15%)-nitrogenfixer/pollinator/native pollarded/coppiced (20%) tree mix with a n fixer perennial understory (eg. white clover/alfalfa,etc) should conservatively yield cca . 500 kg of oily nuts, 500kg chestnuts and 1000 kg of apples (without any outside inputs). Enough food (protein, calories, vitamins,all) for 4 people from one hectare.That is not bad. You can throw in some bean-production for protein in the tree rows (or other vegetables), or alternatively a few sheep,chicken or goat.
Also, this should be managable by handtools and be a regenerative practice in general.
The carrying capacity is pretty amazing in theory.