Sentence:  in a world where there are competing ends for the use of natural resources, and  particularly energy forms, the aim of <WSD>permaculture</WSD> is to create productive systems  which are ecologically sound and ecologically viable, provide for their own ... 
Meaning of the word marked with <WSD> tags:  Any system of sustainable agriculture that renews natural resources and enriches local ecosystems. (from 1978)