I have been looking at Sepp Holzem's work in Austria, and I have seen mention of root depths and patterns as part of designing ecologically compatible guilds. Do you have any good resources for root patterns of plants (specifically common permaculture plants)? This seems to be a very important consideration in creating new guilds.
By the way, already have the book and use it in the high school Urban Farming class I teach in New Orleans. Thanks for making my life easier down here.
Two good resources for learning about plant roots, rooting depths, and related topics: David Jacke's Edible Forest Gardens has a chapter that has many diagrams of root patterns and a detailed discussion of how to use them in design; and Robert Kourik's Roots Demystified: Change Your Garden Habits to Help Roots Thrive which has many diagrams of roots and a lot of information on how to create non-competing interplant arrangements. There's also an older book called High-Yield Gardening by Marjorie Hunt that has many good non-competing polycultures in it with notes about differences in root depth and competition.