(This exercise is based on Ciais, Ph., M. Reichstein, N. Viovy, A. Granier, J. Ogée, V. Allard, M. Aubinet, N. Buchmann, Chr. Bernhofer, A. Carrara, F. Chevallier, N. De Noblet, A. D. Friend, P. Friedlingstein, T. Grünwald, B. Heinesch, P. Keronen, A. Knohl, G. Krinner, D. Loustau, G. Manca, G. Matteucci, F. Miglietta, J. M. Ourcival, D. Papale, K. Pilegaard, S. Rambal, G. Seufert, J. F. Soussana, M. J. Sanz, E. D. Schulze, T. Vesala, and R. Valentini. 2005. Europe-wide reduction in primary productivity caused by the heat and drought in 2003. Nature 437: 529–533.)
(Note: The reference above links directly to the article on the journal’s website. In order to access the full text of the article, you may need to be on your institution’s network [or logged in remotely], so that you can use your institution’s access privileges.)
Global climate change spurred by anthropogenic activity is expected to bring increased temperatures to much of the world in the next decades. Expected patterns of precipitation due to global climate are more variable: some areas will likely have more precipitation, while others will have more and more pronounced droughts.
What will be the consequences of increased temperature and droughts on primary productivity and respiration? These consequences are not just important in terms of ecosystem function and on agriculture, but also for understanding future climate change. A negative feedback cycle will arise if climate change results in an increase in the net ecosystem exchange (or NEE), because the ecosystem would be taking more CO2 out of the atmosphere. In this way, the ecosystem would buffer against further increases of the greenhouse effect. On the other hand, if climate change leads to reduced NEE, then a positive feedback cycle would ensue, as less CO2 is removed from the atmosphere, leading to greater warming, and further decreases in NEE.
A drought in Europe during the summer of 2003 set up the possibility for a natural experiment testing the effects of climate change on productivity, respiration, and the NEE. The continent-wide drought of that year was characterized by elevated temperatures and substantially reduced rainfall. Teams of researchers examined the effects of this heat wave and drought on gross primary productivity (GPP) and respiration by comparing these measures at many different locations across Europe between 2003 and 2002 (a non-drought year).
Table 1 The changes in temperature (ΔT, measured in °C) and precipitation (ΔP, measured in mm) between 2002 and 2003 for the period of July to September. The table also shows changes in GPP (ΔGPP), total ecosystem respiration (ΔTER), and NEE (ΔNEE) for both July–September and for the whole year.
Question 1
Which three sites had the greatest increases in temperature between 2002 and 2003?
Question 2
Which three sites had the greatest decreases in precipitation between 2002 and 2003?
Question 3
Calculate the mean changes in temperature and precipitation between 2002 and 2003.
Question 4
Calculate the mean changes in GPP, respiration (TER), and NEE.
Question 5
Based on the results above, what conclusions can you draw about the effects of the 2003 summer climate on carbon exchange in the ecosystem?
(Note: The following questions require the use of some basic statistical techniques. For a review of various statistical techniques, see the Web Stats Review.)
Question 6
Graph the relationship between temperature change and GPP for July to September for all stations. Then calculate the correlation between temperature change and GPP change. With this number of data points, correlations of 0.473 or greater are statistically significant at the p < 0.05 level. What conclusions can you draw?
Question 7
Graph the relationship between precipitation change and GPP for July to September for all stations. Then calculate the correlation between the change in precipitation and GPP change. With this number of data points, correlations of 0.473 or greater are statistically significant at the p < 0.05 level. What conclusions can you draw?
Question 8
Calculate the correlations between temperature and July–September ΔTER, precipitation and July–September ΔTER, temperature and July–September ΔNEE, and precipitation and July–September ΔNEE. What conclusions can you draw?
Question 9
Given the correlations observed in this study between the climatic factors (changes in temperature and precipitation) and the changes in ecosystem functions (gross primary productivity and respiration), discuss the circumstances under which ecosystem properties will have positive or negative feedback on global climate change.
