LB 23-247 - Indirect effects of moose browsing on ecosystem carbon stocks in Isle Royale, Michigan

Background/Question/Methods:

Carbon stored in biomass and soil in forested ecosystems is driven in large part by forest structure. Forest structure, in turn, depends on climate, disturbance, and herbivory, among other processes. Climate change is likely to cause changes in forest structure and composition, leading to changes in stored carbon. However, bottom-up control of forest structure and composition by ungulate browsers may accelerate or counteract changes associated with a shifting climate if, for example, climate change favors more palatable species. We evaluated the potential for climate change – ungulate interactions at Isle Royale National Park, Michigan, USA, a model system for dynamics of ungulates, predators, and forest structure, using a forest landscape dynamics simulation model (LANDIS-II). This spatially explicit model tracks biomass in forest species-age cohorts and in several soil carbon compartments. The model includes a submodel to simulate spatially and temporally variable browsing by moose, which have been shown to have large effects on forest structure due to selective browsing of juvenile trees.

Results/Conclusions:

Our preliminary results show that climate change is likely to lead to increased dominance by hardwood species, largely driven by the loss of spruce species. Warmer temperatures will likely increase soil respiration, and many sites became carbon sources in our simulations, particularly sites that also lost spruce biomass. Simulated moose browsing led to decreased recruitment of hardwood species and balsam fir, which tend to be highly palatable, partially counteracting temperature-associated species turnover, but reducing the resilience of standing forest biomass. These results highlight the importance of considering multiple trophic levels when evaluating the complex indirect effects of environmental changes.