CTC Visualizations Help Ecologists See The Forest And The Trees

September 19, 1997

Ithaca, N.Y.--- Visitors to this week's edition of ScienceOnline will find a unique new feature, Science's first peer-reviewed article written exclusively as a publication for the World Wide Web. Co-authors Douglas Deutschman (San Diego State University), Simon Levin (Princeton University), Catherine Devine (Cornell Theory Center), and Linda Buttel (Cornell Theory Center) present readers with an interactive introduction to and analysis of the workings of SORTIE, a computer model of forest dynamics based on individual-trees.

The paper, "Scaling From Trees to Forests - Analysis of a Complex Simulation Model," can be viewed at http://www.sciencemag.org/feature/data/deutschman/index.htm.

"The Web site includes scores of still images and a dozen color animations," noted Deutschman. "The 3D results are critical to the readers' understanding the complexity of the model. This is impossible to accomplish in conventional publishing." A built-in feedback feature, moreover, allows visitors to the site to share their thoughts about its success in communicating science.

Deutschman, a theoretical ecologist, is interested in the relationship between a model's complexity and its value as an analytical tool. The team used SORTIE, developed by Steve Pacala (Princeton University), to study the behavior of a model of forest dynamics. SORTIE is an individual-based simulation model of forest dynamics that includes random variation. The behaviors of the trees in the simulations are based on findings from studies done in the Great Mountain Forest (GMF) in northwestern Connecticut.

The model follows each tree in a forest as it competes with its neighbors for light, calculating the response of each tree thousands of times for thousands of trees during each time step. Deutschman worked with Theory Center ecological modeler Linda Buttel to enhance and explore SORTIE, successively looking at the effects of variations in such processes as tree mortality. "This whole exercise is really about identifying details at the individual tree level that are important to the large scale dynamic," explains Deutschman. He ran hundreds of simulations examining different scenarios as the forests evolved over 1,000 years in 5-year time-steps.

The digital output from these simulations was enormous. The technical and artistic challenge of producing high quality videos of the simulations was the job of Catherine Devine, visualization specialist at the Cornell Theory Center (CTC). "Visualizing the results is a key part of exploring a model," says Deutschman. "If you do simulations based on individual trees in 3D, you should be able to look at each tree. That's very difficult to do and that's where Catherine's work came in."

Initially at least 200 frames were rendered at high resolution for each simulation. Final videos included up to 2000 frames per sequence and a video sequence would consume Gigabytes of space for processing. The MPEG movies in the site are custom-compressed 200-to-1 and ended up at about one Megabyte for the Web. In addition, Devine rendered custom images that included such details as sapling trees and canopy geometry.

"This work is part of our broader program to understand how much detail at the level of individuals is needed to understand the macroscopic dynamics of ecosystems," says Levin, Director of the Princeton Environmental Institute. "The forest growth work, which builds on a model developed by Steve Pacala and others, represents the most important advances to date."

The Cornell Theory Center is supported by the National Science Foundation, New York State, the National Center for Research Resources at the National Institutes of Health, IBM, and other members of CTC's Corporate Partnership Program.

For more information, contact:

Linda Callahan
Director of External Relations
Cornell Theory Center
Phone: (607) 254-8610
FAX: (607) 254-8888
e-mail: cal@tc.cornell.edu

Louise Snider
Communications Officer
University Communications
San Diego State University
Phone: (619) 594-5204
FAX: (619) 594-5956
e-mail: lsnider@mail.sdsu.edu

Cornell Theory Center

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