Its worth noting somewhere that the term sustainable or sustainability is heavily deprecated among Greens and especially Gaians for implying some kind of steadystate output  In other words ecological yields vary and can be maximized but will still vary considerably with weather patterns insect migration paths and etc they cant be made as uniform as outputs of a factory  which almost seems to be the goal of sustainability  Also to say something is sustainable or not implies that there is some actual test for it  Which there isnt  Its all a matter of scenarios and guesses  The Limits to Growth type of numerical modelling largely discredited now was the actual origin of the sustainable paradigm  Today ecologists are far more concerned with homeostasis keystone species and homeorhetic process none of which benefit much from external measures of sustainability  Complex problem  Dont pretend to have an answer or a clear altnerative term