ecological yield

The ecological yield is the output of ecological commodities over a period of time, e.g. board-feet of wood, edible calories in fruit or grasses, etc. It is the most basic (but incomplete) way to measure the value of natures services.

David Suzuki pointed out that if the interest rates on debt exceeded the ecological yield, then, over time, any ecosystem whose yield was the sole way to pay that debt would be necessarily destroyed: if it grew back at 2% per year but was forced to yield 3%, then, over time, the natural capital must all be lost.

See http://en.wikipedia.org/wiki/ecological_yield for a general reference.