ECOSYSTEMS AS RESOURCES
I. Why Do We Want to Use Resources Sustainably?
A. Resources provided by ecosystems sustain life. B. There are a limited number of resources in an ecosystem. C. Ecosystems are limited in their ability to cycle resources.
II. Ecosystems and Their Goods and Services
A. The Goods (Resources) a. Wood: buildings, paper, furniture b. Food: meat, grains, vegetables, fruits, oils c. Minerals: phosphorus and nitrogen (for farming), copper (electrical wire), aluminum (cans, cars), iron, silver, gold, platinum, titanium d. Fuel: wood, petroleum, dung, alcohol e. Clothing: cotton, rayon, nylon, polyester, fur, leather f. Plastics: petroleum, trees (rayon) B. The Services 1. Maintenance of Hydrologic Cycle: water infiltrates soil and is absorbed by plants. Water evaporates from soil or evapotranspires from plants. Evaporated water condenses in the atmosphere and falls to the earth as precipitation. Flooding is prevented by the functioning of dynamic ecosystems because precipitation is absorbed by the ecosystem and slowly released. 2. Modification of Climate: Water absorbs a considerable amount of energy from the sun as it evaporates. This energy is released when the water condenses. Heat is moved around the planet in water. 3. Erosion Control and Soil Building: Plant and detritus control erosion by absorbing the impact of precipitation, and make a greater surface area available for the absorption of water. Plants, animals, and microorganisms found in terrestrial ecosystems create soil. 4. Maintenance of Oxygen and Nitrogen Cycles: Photosynthesis releases oxygen. Nitrogen fixing microorganisms in the soil maintain soil fertility. 5. Waste Treatment: Water is a universal solvent. Many water-soluble pollutants (sediments, excess nutrients) are removed from the water in wetlands. 6. Transformation of Toxic Chemicals: Microorganisms transform many toxic chemicals, both organic and inorganic, into harmless products. [The opposite is true also. The Minamata Bay disaster resulted when inorganic mercury was released in industrial effluent and transformed by microorganisms into organic mercury.] 7. Pest Management: Predators for the organisms we consider pests exist. When predators are maintained, pest management is provided by ecosystems. 8. Carbon Storage and Maintenance of the Carbon Cycle: Carbon is cycled through the atmosphere, biomass, and soil. The biomass of the forest contains 500 billion metric tons of carbon more than is found in the atmosphere. Even more carbon is found in the organic matter of soil
Fig. 12.4 Worth more than $100,000 a year for just one acre, these services are lost when wetlands are bulkheaded and converted for vacation homes.
B. Monetary Benefit of Ecosystems
1. A 1997 study estimated that the world's ecosystems provide $33 trillion worth of goods and services per year. 2. One acre of wetlands does the equivalent of $100,000 per year of water purification and fish propagation services. 3. We undervalue the services of ecosystems because their services are provided free of charge. 4. We notice the services when they are gone: a. The eutrophication of Chesapeake Bay is a result of wetland loss and an increase in the added nutrients within its watershed. b. Flooding in Bangladesh is a result of deforestation in India; consequently, the monsoons cause great loss of human life and devastation of crops.
III. Patterns of Use of Natural Ecosystems
A. Consumptive versus Productive Use 1. In consumptive "people harvest natural resources in order to provide for their needsfor food, shelter, tools, fuel and clothing." 2. "Productive user refers to the exploitation of ecosystem resources for economic gain." B. "A natural ecosystem will receive protection only if the value society assigns to its natural function is higher than the value the society assigns to exploiting its natural resources." 1. This is a conflict between individual gain from and societal loss of the goods and services provided by an ecosystem. 2. This conflict also occurs between those who use public land for private gain (ranchers, loggers, miners, etc.) and those who want the ecosystem conserved in a way that produces the greatest good for the largest number of organisms (humans included.) C. Maximum Sustained Yield (MSY): "The highest possible rate of use that the system can match with its own rate of replacement or maintenance." 1. How does MSY works? At low population size the rate of population growth will increase because the environmental resistance factors are low. At low population size, the rate of population growth will increase until environmental resistance factors begin to limit population size. This point is MSY. As the population size becomes larger than the MSY, the rate of growth population decreases and the number of individuals that can be extracted does not increase. 2. MSY is the point where the highest rate of recruitment can occur. The highest rate of harvesting can occur at the point where the highest recruitment occurs. 3. The difficulty with MSY is determining it. We typically do not know the point at which the highest recruitment occurs. 4. For example, North Sea cod were overfished because we do not understand
Fig. 12.8 Maximum sustainable yield occurs not at the maximum population level, but rather at a lower, optimal population level.
Fig. 12.12 This figure shows the global fish catch and fish farming equals world total for 1950-97
Fig. 12.10 In the U.S. only 17% of wood is used for fuel.
Fig. 12.14 This method of harvesting groundfish has been compared to clear-cutting forests because of degradation of the bottom.
D. Tragedy of the Commons: When a resource is held in common or by no one, it is known as a commons. 1. Grasslands (grazing, mining) 2. Coastal and open ocean (fishing, mining) 3. Groundwater (urban and agricultural use) 4. Woodlands and forests (logging, mining)
IV. Ecosystems Under Pressure
A. Forests and Woodlands 1. Threat: Total Removal 2. Consequences: loss of biomass, reduced productivity, reduced biodiversity, soil erosion, changed hydrologic cycle, loss of carbon dioxide sink B. Ocean Ecosystems 1. Threat: Overexploitation 2. Consequences: Reduced productivity and reduced biodiversity C. Grasslands 1. Threat: Total Removal 2. Consequences: Loss of biomass, reduction in biodiversity, loss of carbon dioxide sink, changed hydrologic cycle, and soil erosion
Fig. 12.16 Because the East and Midwest were settled first, federally-owned lands are concentrated in the West and Alaska.
Fig. 12.17 The National Park is the center of a much larger ecosystem receiving attention from the Greater Yellowstone Coalition.
Fig. 12.13 This figure shows cod landings from Georges Bank, 1982-96.