permaculture

[sinergyinaction@netscape.net]

Hi
is there any way to predict how productive a forest garden could be?
Or put it another way, how much surface area might be needed for a forest 
garden to feed
a specified number of people on a given climate year round? In may case a 
mediterranean climate with 500 ml rainfall (and access to municipal water).
I am talking about the daily ration of fruit of an "average" person, not 
necessarily vegetarian.

What variables do we need to consider?
Cheers
Antonio