Carbon dioxide and plant growth. The concentration of carbon dioxide (CO2) in the atmosphere is increasing rapidly due to our use of fossil fuels. Because plants use CO2 to fuel photosynthesis, more CO2 may cause trees and other plants to grow faster. An elaborate apparatus allows researchers to pipe extra CO2 to a 30-meter circle of forest. They set up three pairs of circles in different parts of a forest in North Carolina.
One of each pair received extra CO2 for an entire growing season, and the other received ambient air. The response variable is the average growth in base area for trees in a circle, as a fraction of the starting area. Here are the data for one growing season:
(a) Summarize the data. Does it appear that growth was faster in the treated plots?
(b) The researchers used a matched pairs t test to see if the data give good evidence of faster growth in the treated plots. State hypotheses, carry out the median increase in heart rate and apply the Wilcoxon signed rank test. What do you conclude?