A function is something useful that a plant or animal does. For example, a tomato plant provides food for the gardener.
Plants and animals can perform more than one function. For example, a tree can cast shade to keep a house cool in summer, offer a place for birds to nest, and produce fruit for people to eat. This concept is called ‘stacking functions’. Permaculture practitioners strive to use space efficiently by incorporating plants that can perform many functions.
Permaculture practitioners also emulate nature by having a ‘back-up’ for each function. That is, they aim to have each function performed by multiple elements, so that if one element fails, another is ready to take over the function. For example, a gardener might add several types of plants that attract beneficial insects.
A yard that performs many functions makes less work for the gardener. By casting shade, trees minimize evaporation, so less watering is needed. Plants that make nutrients available to other plants reduce the need for fertilizer, while a few backyard chickens will gobble down insects and weeds, making pesticides unnecessary. By arranging elements so that nature does the work, we can have a more vibrant yard and more time to spend enjoying it.