The seminal work on this topic is 'Edible Forest Gardens' by Jacke and Toensmeier, but there are others that have ecosystem design chapters; for example the boo

The seminal work on this topic is 'Edible Forest Gardens' by Jacke and Toensmeier, but there are others that have ecosystem design chapters; for example the books by Martin Crawford (also see his website www.agroforestry.co.uk for literature if you don't want to buy books just for a quick read). The gist of it is that in balanced ecosystems, you have natural remedies against pests; birds against insects for example, or certain plants that repel insects, or plants to combat diseases, or predators that eat insects that distribute diseases. This is the theory; currently there is little evidence (as in, scientifically valid results, not anecdotes) that this works as it's claimed. I'm working on an experimental food forest to test some of these concepts. There are many things I'm very skeptical of, but in the mean time I have an excuse to work outside in the field, so hey...