SYMP 11-3 - Forest productivity and carbon storage under climate change: A game-theoretic perspective

Wednesday, August 9, 2017: 9:00 AM
Portland Blrm 251, Oregon Convention Center
Ray Dybzinski, Institute of Environmental Sustainability, Loyola University Chicago, IL

Height competition for light among trees is almost certainly the consequence of a game-theoretic eco-evolutionary dynamic that affords taller individuals relative benefits that come at an absolute collective cost to the community (e.g. diversion of carbon, risk of wind damage). Simply put, real trees massively over-allocate to wood compared with a hypothetical “tree” that evolved free of height competition. Theory and experiments suggest that similar game-theoretic pressures may cause trees to over-allocate to roots, foliage, and fecundity.

In contrast, conceptual and mathematical models that assume trees (merely) optimize their allocation to match resource availability have historically dominated – and continue to dominate – conventional thinking about trees. Such models do not predict over-allocation. What are the consequences of holding this conventional perspective if game-theory actually determines tree allocation strategies? Is it akin to guiding biological research from a Lamarckian perspective in a Darwinian world? (i.e. a big problem!) Or is it akin to guiding architectural research from a Newtonian perspective in a quantum-theoretical/relativistic world? (i.e. perfectly adequate for the task!)

To answer this question, I developed a forest allocation model that has the unique ability to shift between a conventional “game-off” model and a game-theoretic “game-on” model, allowing an “apples-to-apples” comparison.


For the dimensions that I investigated (foliage, wood, fine root, fecundity, & total NPP; C:N; nitrogen uptake; and nitrogen limitation across separate gradients of nitrogen availability, atmospheric [CO2], and growing season length), the qualitative results are similar but the quantitative results are divergent between the “game-off” and “game-on” versions of the model. For example, foliage NPP is predicted to qualitatively increase with growing season length regardless of model type, but with a 2- to 5-fold quantitative difference depending on which games are “off” or “on.”

The qualitative agreement between the “game-off” and “game-on” models suggests that conventional conceptual or mathematical models can be “fit” to a game-theoretic reality, which would explain why the conventional perspective may appear unproblematic even if the game-theoretic reality is in fact True. If that is what’s going on however, two “sticky problems” emerge: (1) our conceptual understanding of plant strategies could be largely mistaken, with attendant problems, and (2) although interpolations of fit phenomena may serve us well, extrapolations likely won’t. I end with a case study in root over-proliferation that demonstrates how these “sticky problems” may confuse our understanding of allocational responses to elevated CO2, leading to bad extrapolations in Earth system models.