Diversity; including guilds
Diversity is relevant to future planning, by creating a diverse crop base you can be prepared for the future. Consideration of the species you are planting amongst the others is important as some may compete for water, light and nutrients. Diversity enables stability and anticipation of weather conditions that can eliminate a specific crop, planning can prevent this scenario from leaving the community with less crops and food produce. "So the importance of diversity is not so much the number of elements in a system; rather it is the number of functional connections between these elements." Mollison and Slay.
This is where a main element (such as a plant or animal) is surrounded by plants that complement the other. This can simply mean that the surrounding elements do not harm each other, which allows them to work together and share the resources needed. "Hence the concept of guilds which rely on composition and placement of species which benefit (or at least do not adversely affect) each other." Mollison and Slay.
Image: London Permaculture