Rigorously analyzed data suggest that our environment is changing in important ways. Average temperatures are rising, atmospheric carbon dioxide is increasing and soils are becoming laden with biologically active nitrogen. The effect of these changes on ecosystems is unknown, but the nature of these changes will depend heavily on the stability of the ecosystems that we have.
Global biodiversity levels are falling, and the diversity of many regional ecosystems shows a corresponding drop. While it is likely that much of this decrease is primarily driven by anthropogenic disturbances such as land-use change and exotic species introduction, climate change might also be affecting habitats. Rainfall patterns, temperatures, and nutrient availability can influence biodiversity, species distribution, and ecosystem function, the three of which are complexly linked together themselves. It is hoped that the results of the following Cedar Creek experiments will aid in the formation of new environmental models and guide adaptive management strategies.
Human activities have doubled the natural terrestrial rate of fixed nitrogen formation (Vitousek 1994, Vitousek et al. 1997). Currently, atmospheric deposition of nitrogen ranges from about 0.5 to 2.5 g per square meter per year in the US and from 0.5 to 6.0 g per square meter per year in Europe (Matthews 1994, Galloway et al. 1995.) The doubled global food demand projected for the year 2050 (Cohen and Federoff 1999) and trends in nitrogen fertilizer use suggest that nitrogen deposition will be about two times higher by mid-century (Tilman et al. 2001).
Five key experiments at Cedar Creek address long-term N deposition
Experiment 001, Experiment 002 and Experiment 141, examine the effects of nitrogen and nutrient addition on undisturbed and disturbed savanna prairie habitats. Since its initiation, e002 has been subdivided to include two new experiments that test recovery from long-term nitrogen addition and the interactive effects of burning.
Experiment 145 and Experiment 211 look at the impact of nitrogen fertilization on litter and soil decomposition, and examine its role as a limiting factor.
Experiment 120: One of the largest experiments established at Cedar Creek, “BigBio” is used to study how plant species diversity affects population, community, and ecosystem processes. Since biodiversity is also dependent on environmental conditions, related experiments look at the combined impacts of biodiversity and climate changes such as nutrient increase or global warming.
Experiment 141: BioCON examines the interactive effects of carbon dioxide and nitrogen availability on biodiversity. Technological advancements during the Industrial Revolution captured the immense power of fossil fuels as sources of power, but burning them released billions of tons of carbon dioxide into the air. Since the mid-19th century, carbon dioxide concentrations in the atmosphere have increased by approximately 50%. While both carbon dioxide and nitrogen are essential plant nutrients, their increased availability in the ecosystem is unprecedented in human history and the effect this will have on plant growth is not entirely known.
Experiment 249: In addition to pumping carbon dioxide into plant ecosystems, the greenhouse gasses released by modern industry has contributed to global warming. Estimates for Minnesota suggest that temperatures will rise an average of 2-7 °C (4-13 °F) within the next 70 years. The BAC experiment simulates this projected increase in temperatures in plots with varying biodiversity.
Vitousek, PM. 1994. Beyond global warming-ecology and global change. Ecology 75:1861-1876.
Vitousek, PM, JD Aber, RW Howarth, GE Likens, PA Matson, DW Schindler, WH Schlesinger, and GD Tilman. 1997. Human alteration of the global nitrogen cycle: sources and consequences. Ecological Applications 7:737-750.
Matthews, E. 1994 Nitrogenous fertilizers: global distribution of consumption and associated emissions of nitrous oxide and ammonia. Global Biogeochemical Cycles 8:411-439.
Galloway, JN, WH Schlesinger, H Levy II, A Michaels, and JL Schnoor. 1995. Nitrogen fixation: atmospheric enhancement-environmental response. Global Biogeochemical Cycles 9:235-252.
Cohen, JE and NV Federoff. 1999. Colloquium on plants and population: Is there time? National Academy of Sciences, Washington, D.C.
Tilman, D., J. Fargione, B. Wolff, C. D’Antonio, A. Dobson, R. Howarth, D. Schindler, W. Schlesinger, D. Simberloff, D. Swackhamer. 2001. Forecasting Agriculturally Driven Global Environmental Change. Science 292:281-284.
