Martin Crawford of the UK’s Agroforestry Research Trust is one of the world’s best recognised practitioners of the art of “forest gardens”.
Martin’s forest garden has an enormous diversity of plants. Most, but not all, are edible. Those that are not edible would be regarded as a waste of space to most farmers or gardeners, but these also serve valuable purposes and earn their keep in the garden — ultimately also being responsible for not only increased resiliency, and thus less labour input, but also increased productivity. Some attract beneficial insects, or insect-eating birds. Some may distract/confuse the more troublesome insects by their colour and scent. Some may provide sustenance and habitat for pollinators. Some are bio-accumulators (i.e., for example, they might bring minerals up into the soil profile layers where they can later be accessed by other food-producing plants), or some might provide protection from wind and extreme temperatures to their more fragile peers.