Martin Crawford is one of the world leaders in Forest Garden design. He is the author of the book, Creating a Forest Garden.
From his Wikipedia Page:
Martin Crawford is Director of the Agroforestry Research Trust, a British charity which conducts research into temperate agroforestry.
Martin Crawford has spent over twenty years in organic agriculture and horticulture and is director of The Agroforestry Research Trust, a non-profit-making charity that researches into temperate agroforestry and all aspects of plant cropping and uses, with a focus on tree, shrub and perennial crops. It produces several publications and a quarterly journal, and sells plants and seeds from its forest gardens.
He has been on BBC Radio shows The Food Programme and Gardener's Question Time.
The Food Programme: Forest Gardens http://www.bbc.co.uk/iplayer/console/b010xy3g
Gardener's Question Time: Forest Gardens: http://www.bbc.co.uk/programmes/b014641y
(his interview occurs at about 31 minutes into the show)
Gardener's Question Time: Nut Trees: http://www.bbc.co.uk/programmes/b017clwz
(his interview occurs at about 31 minutes into the show in this one as well)