Hello,
As a scientific comparison it will be difficult to compare say a mono orchard with a perma one, also it wouldnt be correctly comparing the perma fairly, for example a orchard is only one part of a permaculture set up, or a part of one zone even.
Maybe you could compare it per acre for example,
because in permaculture you have so many layers,
root crop, salad crop, herb crop, shrub and berry crop, small trees, large trees, fungi etc etc, that not including the other benefits from feeding your animals etc etc etc.
so that root veg, leaf veg, herbs, berries, fruits like
apple pairs etc, nuts. in the
apple orchard you just get x apples or in a lettuce field x amount of lettuce.
also you have other factors, like risk, in a permaculture you have far less of a chance that your crop will be ruined by draught, or to muc rain or pests insect and mammals.
so on the permaculture you solves these problems by careful observation and working with nature, mono uses fossil fuel based insectacides, herbicides etc etc which cost money to buy and administer on a large scale often having to have large machinery, thats without the huge issue of
irrigation.
which brings us to yield, this ofc isnt just about how much is grown but how much work and money it takes you to get to that point aswel. so start your diso with this in mind.
You need to speak to some people who have advanced forest gardens, I heard of a guy in England called Martin Crawford that has been doing this long
enough to have a mature forest garden, perhaps you could find his website and e-mail him.
hope this helps a little mate.