The joke about the washing line being a solar clothes dryer is humorous because we recognise that we have been conned into using unnecessary and complex gadgets for simple tasks. While anyone would recognise line drying of clothes as miles ahead in the sustainability stakes compared to using an electric tumble drier, fewer people acknowledge wood as an environmentally appropriate fuel. All forests generate surplus low-value wood as a by-product of sustainable management which, when properly seasoned (more solar drying) can be used as a local source of heating and cooking in well designed stoves. In the same way that wood does not meet all criteria we might want from a fuel, herbal medicine might not provide a complete pharmacopeia, but we can, to a very great extent, successfully treat many ailments with locally grown and processed botanical medicines. By doing so, we avoid many adverse side effects both internal and external from centralised drug production, increase our respect for nature, and feel more confident in maintaining our own health.
Renewable services (or passive functions) are those we gain from plants, animals and living soil and water, without them being consumed. For example, when we use a tree for wood we are using a renewable resource, but when we use a tree for shade and shelter, we gain benefits from the living tree that are non-consuming and require no harvesting energy. This simple understanding is obvious and yet powerful in redesigning systems where many simple functions have become dependent on non-renewable and unsustainable resource use.
Classic permaculture designs using chickens or pigs to prepare ground for planting bypass the use of tractors and rotary hoes, as well as artificial fertiliser and pesticides. In these systems, a modicum of management and fencing allows a more sophisticated use of livestock for multiple functions.
Permaculture design should make best use of non-consuming natural services to minimise our consumptive demands on resources, and emphasise the harmonious possibilities of interaction between humans and nature. There is no more important example in history of human prosperity derived from non-consuming use of nature's services than our domestication and use of the horse and other animals for transport, soil cultivation and general power for a myriad of uses. Intimate relationships to domestic animals such as the horse also provide an empathetic context for the extension of human ethical concerns to include nature. On the other hand in cultures where livestock are still prevailing symbols of meaning and wealth, the more fundamental renewable services provided by plants and soil life need to be recognised, valued and used. In both rich and poor communities realising the value of human waste as a renewable source of fertility made safe by the ecological service of microbes in a compost toilet is one of the important and universal applications of this principle.
The proverb Let nature take its course reminds us of another aspect of this principle - that the pursuit of total control over nature through use of resources and technology is not only expensive, but can also lead to a spiral of intervention and degradation in biological systems and processes which already represent the best balance between productivity and diversity.
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