Elicitation of expert judgments of climate change impacts on forest ecosystems

Detailed interviews were conducted with 11 leading ecologists to obtain individual qualitative and quantitative estimates of the likely impact of a 2 × [CO2] climate change on minimally disturbed forest ecosystems. Results display a much richer diversity of opinion than is apparent in qualitative consensus summaries, such as those of the IPCC. Experts attach different relative importance to key factors and processes such as soil nutrients, fire, CO2 fertilization, competition, and plant-pest-predator interactions. Assumptions and uncertainties about future fire regimes are particularly crucial. Despite these differences, most of the experts believe that standing biomass in minimally disturbed Northern forests would increase and soil carbon would decrease. There is less agreement about impacts on carbon storage in tropical forests. Estimates of migration rates in northern forests displayed a range of more than four orders of magnitude. Estimates of extinction rates and dynamic response show significant variation between experts. A series of questions about research needs found consensus on the importance of expanding observational and experimental work on ecosystem processes and of expanding regional and larger-scale observational, monitoring and modeling studies. Results of the type reported here can be helpful in performing sensitivity analysis in integrated assessment models, as the basis for focused discussions of the state of current understanding and research needs, and, if repeated over time, as a quantitative measure of progress in this and other fields of global change research.