1. Sustainability: A systems view John Rueter Environmental Sciences Program Portland State University

2. Definition of “Sustainability” Brundtland Report  “development that meets the needs of the present without compromising the ability of future generations to meet their own needs”

3. Importance of natural capital Natural capital includes all the resources in the natural world that can be mined or harvested “Strong Sustainability” means that natural capital has to be maintained “Weak Sustainability” means that we can replace natural capital with physical capital or human capital I will focus on Strong Sustainability

4. Systems view of the problem Example:  growth of a biological system (forest) Flows in and out of reservoirs Information links Good for examining limitations

5. Natural limitations to growth Maximum growth rate controls growth rate at low populations Carrying capacity limits population size at high populations

6. Systems view of sustainability Resource production must at least equal harvest

7. Three ways to be unsustainable Over harvest Degradation of the conditions for growth Bad luck

8. Over exploitation will decrease production If harvest > growth then the forests will decline

9. Harvest activities may decrease production Some activities may destroy the capacity of the system Examples: pollution, too many roads, others

10. Bad luck can have long term effects When harvesting close to the maximum sustainable yield, a bad year can have long lasting, even catastrophic effects Example:  Constant harvest  Year 3 only 50% of production  Underestimate maximum growth by 5% Sustainable level

11. Conclusions Replacement of natural capital is an important part of “strong sustainability” Natural systems are susceptible to:  Over harvesting  Degradation of conditions  Bad luck

12. References Brundtland Commission, 1987. World Commission on Environment and Development

13. Contact information John Rueter Environmental Science Program Portland State University PO Box 751 Portland, OR 97207-0751 rueterj@pdx.edu http://web.pdx.edu/~rueterj

14. Maximum sustainable yield Harvest of the natural products is maximum when a mid-level population size is growing at a high rate Maximum sustainable yield Example: Algae growth