Global modeling and prediction of climate-induced forest dieback

The potential for widespread forest dieback under rapid global warming was forecast as a possibility, strictly from conceptual principles, as early as 1993.  Today, forest dieback is appearing in many different ecosystems, ranging from Pinyon-Juniper Woodlands in the Great Basin to Lodgepole Pine in British Columbia.  Drought, followed by insect infestation is often cited as a proximate mechanism.  So, too, are warmer winters and the lengthening of the growing season from global warming, allowing the biogeographic spread of bark beetle outbreaks as well as shortening from two to a single year the time for completion of the beetle’s life cycle.  High-severity wildfires appear to be increasing.  Even Boreal ecosystems, once thought to be primarily radiation limited, may be exhibiting signs of temperature-induced drought stress.  Dynamic General (Global) Vegetation Models (DGVMs) are a recent invention and were designed to simulate the dynamic change in vegetation distribution with climate change, its growth and potential decline from drought stress with disturbance by fire.  However, as yet, DGVMs are incapable of simulating insect infestations or disease impacts.  Mortality of trees is also not well understood.  As dominant forest species shift spatially through mortality and migration in response to rapid climate change, the potential for catastrophic disturbances looms, yet our ability to forecast these processes is still limited.  Examples of our capabilities and a discussion of our forecasting limitations will be presented.