About the Speaker
Stephen W. Pacala is the Frederick D. Petrie Professor of Ecology and Evolutionary Biology at Princeton University. He co-directs the Carbon Mitigation Initiative, an effort to develop solutions to the greenhouse warming problem. Steve is also on the Board of the Environmental Defense Fund, and is a founder and Chairman of the Board of Climate Central, a nonprofit media organization focusing on climate change. Professor Pacala has researched a wide variety of ecological and mathematical topics. At Princeton, his work focuses on problems of global change with an emphasis on interactions among the biosphere, greenhouse gases and climate. He also researches solutions to the climate problem, the dynamics of forests, and the relationship between biodiversity and ecosystem function.
Professor Pacala completed an undergraduate degree at Dartmouth College and a Ph.D. in Biology at Stanford University. His honors include the David Starr Jordan Prize, the George Mercer and Robert MacArthur Awards of the Ecological Society of America, and election to the American Academy of Arts and Sciences and the U.S. National Academy of Sciences.
Earth System Models that predict climate include a land model that predicts the dynamics of vegetation and undecomposed organic matter, and exchanges of matter, energy and momentum between land surface, vegetation and atmosphere. Over the past two decades, my group has worked to discover equations that scale correctly from plant physiology to populations and ecosystems. We also design the terrestrial ecosystem component of NOAA (GFDL) Earth System Models. The ED land model, which is currently being developed by the DOE, including at Lawrence Berkeley, was originally developed in my lab 15 years ago.
ED is based on a mathematical technique to scale up the dynamics of large numbers of interacting individual plants, analogous to methods used in statistical physics. One difficulty with the ED approximation is that it produces analytically intractable equations, which limits one’s capacity to understand it. For this reason, we subsequently developed an alternative approximation (called the PPA) that produces analytically tractable equations and is used in the new NOAA-GFDL land model. This seminar will explain the PPA and describe four applications of it and what we learned though them:
The reason for the PPA’s novel prediction that carbon sinks from CO2 fertilization will not disappear because of limited nitrogen, which explains results from large-scale CO2 enrichment experiments. The reason for the amazingly tight power law relationship between the number of individuals and their diameter in all the world’s tropical rainforests, and why the cause of this power law is responsible for a large fraction of the carbon stored in these ecosystems. How unavoidable constraints imposed by a tree species’ ratio between leaf area and leaf mass determines the mix of evergreen and deciduous trees in the temperate and boreal zones.