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Plant toxins and trophic cascades alter fire regime and succession on a boreal forest landscape

Mathematical Biology

Speaker: Zhilian Feng, Purdue University
Location: 2112 MSB
Start time: Mon, Feb 27 2012, 3:10PM

Two models were integrated in order to study the effect of plant toxicity and a trophic cascade on forest succession and fire patterns across a boreal landscape in central Alaska. One of the models, the `toxin-dependent functional response' model (TDFRM) incorporates woody vegetation types with different levels of toxicity, an herbivore browser (moose) that can forage selectively on these types, and a carnivore (wolf) that preys on the herbivore. This model exhibits complex dynamics represented by various bifurcations. The other model, ALFRESCO, is a cellular automata model that stochastically simulates transitions from spruce to deciduous woody vegetation based on stochastic fires, and from deciduous woody vegetation to spruce based on age of the cell with some stochastic variation. Here we replace the simple succession rules in ALFRESCO simulations by plant-herbivore-carnivore dynamics from TDFRM. The central hypothesis tested in the integrated model is that the herbivore, by feeding selectively on low-toxicity deciduous woody vegetation, speeds succession towards high-toxicity evergreens, like spruce. Wolves, by keeping moose populations down, can help slow the succession. Our results confirmed this hypothesis for the model calibrated to the Tanana floodplain of Alaska. We used the model to estimate the effects of different levels of wolf control. Simulations indicated that management reductions in wolf densities could reduce the mean time to transition from deciduous to spruce by more than 10 years, thereby increasing landscape flammability. The integrated model can be useful in estimating ecosystem impacts of wolf control and moose harvesting in central Alaska.