Problem 2
Low-growing tundra vegetation is being slowly replaced by faster growing shrubs like willows as global warming continues (Sturm et al. 2005). What effect might this change in vegetation have on the \(\mathrm{CO}_{2}\) dynamics of tundra ecosystems? Discuss what you would need to measure to test your ideas. Mack et al. (2004) provide some data on this issue.
Problem 5
Red squirrels in the southwestern Yukon of Canada have advanced their season of birth in spring by more than two weeks over 10 years, associated with climatic warming. Red squirrels breed in midDecember in the middle of winter and have a fixed gestation period. Discuss how this change in birth season might happen and what the mechanism might be for detecting a change in climate. Réale et al. (2003) discuss this issue.
Problem 6
Discuss why experiments on the impact of increased \(\mathrm{CO}_{2}\) levels on crop growth should give different answers when conducted in the greenhouse and when conducted in open fields with FACE technology. Long et al. (2006) discuss this problem.
Problem 7
Norby et al. (1992) grew yellow poplar (Liriodendron tulipifera) trees for three years at three levels of \(\mathrm{CO}_{2}\) enrichment. Photosynthetic rate nearly doubled at high \(\mathrm{CO}_{2}\) levels, but no difference in aboveground biomass of trees grown at normal or elevated \(\mathrm{CO}_{2}\) levels was found after three years. How is this possible?
Problem 9
In agricultural landscapes, farmers have the choice of managing roadside verges by mowing, burning, grazing, or doing nothing to them. Discuss the implications of these four treatments for the global carbon cycle.
