The Forest Garden Permaculture is about designing sustainable human environments. By gradually moving from an annual to a perennial system, the process becomes more self-sustaining. Annuals will produce more and faster, but the input required for growing is higher than for perennials. Often, some thinning is needed and either mulch or compost added again before the harvest.
Water is essential for most annuals.
One strategy used is to let some of the annuals go through their whole cycle, flowering and then producing seeds. Some can be collected, others will fall to the ground where they will sprout and start growing when the environment is favourable. In this way, some annuals can become perennials. Using more perennials in your design will help in the long run to have a more sustainable system, by cutting down on the amount of work needed to maintain the plants. Perennnials don't need to be seeded or planted every year.