Text: Energy and Nutrient cycling
1) You are conducting a study on the effects of fire exclusion across two watersheds in a temperate forest in Oregon. In one watershed, any wildfires have been rapidly extinguished and no prescribed burns have been conducted for the last 100 years, leading to a buildup of pathogens and parasites on the dominant tree species. In the other watershed, prescribed fires have been used as a management strategy every 10 years over the same window of time, periodically removing small understory plants and releasing some of the nutrients that had been sequestered in the burned plant tissue back into the watershed.
a. In which watershed might you expect to find more biomass? Where would you expect to find more sequestered carbon (in both living and dead tissue)? Explain.
b. In which watershed might you expect to find higher GPP? What about higher NPP? Explain.
2) What accounts for the observation that on average, each trophic level in an ecosystem only holds about 10% of the biomass of the trophic level directly below it? How does this relate to the fact that all the largest animals on earth (e.g. blue whales) are primary consumers?
3) Can energy be recycled indefinitely within an ecosystem? What about nutrients? Discuss what your answers imply regarding the need for continuous inputs of both matter and energy in order for an ecosystem to continue functioning.
4) Name and justify the factor you would expect to be the main constraint on productivity in:
a. A desert ecosystem in the southwest United States?
b. The bottom of the Atlantic Ocean?
c. A tropical rainforest?
d. The Siberian Tundra?
5) Using your understanding of trophic energy transfer efficiency, make the case that a vegetarian diet is objectively a more efficient and sustainable diet. Explain.