Soil, forests, watersheds, fisheries, fresh water sources, river estuaries, and the atmosphere - ecosystems generally - are self-regenerative, but suffer from depletion or deterioration when they are over-used. (In the extreme are exhaustible natural resources like oil and natural gas). Despite the neglect, a number of economists in recent years have been trying to include Nature into economic models in a seamless way. These Notes offer a very brief introduction to the way we have done that.