For your consideration, from a forestry perspective, I often pose to students during their oral examinations or thesis defenses a question on sustainability. The main purpose is to see what definition of sustainability they use, and the discussion usually brings forth their values concerning sustainable systems. But, I also want them to think more broadly about all kinds of ecosystem services, and whether human use of the land is sustainable over the long-term. It is often instructive, but sometimes frustrating. Has anyone found this a useful exercise for graduating forestry or environmental science students?