Gradual global environmental change in the real world and step manipulative experiments in laboratory and field: The necessity of inverse analysis

Ecosystem responses to perturbation generated by a step increase in climatic variables, such as CO₂ concentration and temperature as in field manipulative experiments, are different from responses as a result of a gradual increase in climatic variables as in the real world. This chapter discusses how results from manipulative experiments can be analyzed to improve our predictive understanding of ecosystem responses to future gradual climate change. We first describe gradual changes in several global environmental variables and the corresponding manipulative experiments. Then we review a modeling study by Luo and Reynolds (1999) on differential responses of ecosystems to gradual vs. step changes in CO₂ concentration. We also review results from several experiments to verify that ecosystem responses to step CO₂ increases are different from those to gradual changes. Finally, we introduce a framework of analysis techniques - inverse analysis - that extract information from experimental data toward predictive understanding in ecological research. The inverse analysis fundamentally focuses on data analysis for parameter estimation and evaluation of alternative model structures so as to improve our predictive understanding from both experimental observations and prior knowledge about the ecosystem processes.