Forest Farming

In the latest episode of Big Dreams Small Spaces Monty Don took an allotment holder to a 'forest farm' to look at vegetables, fruits and herbs that will grow under and through trees. Does anyone have any experience of this? I can't find any information on the internet except US sites. I'd love to find some fruits, perennial vegetables or herbs which would grow under my trees. I remember mention of a blackberry, but these grow everywhere wild around us.