With the onset of a warming climate and the potential for increased periods of drought in the Lake States, ecosystems dominated by jack pine are likely to experience more frequent and severe wildfires, with potential impacts on a multitude of ecosystem services. Quantifying the dynamics of vegetation structure and fuel loadings in these systems in ways that will inform predictions of successional pathways and/or fire behavior is critical. Quantitative data describing how vegetation and fuels change over time to influence flammability in this system could therefore be important for its translation into decision-making aids for managers as they begin to reinstate the practice of prescribed burning.
Plant indicator species groups developed specifically for these jack pine-dominated systems were less able to differentiate ecosystems across the landscape as succession proceeded, likely because their coverages decreased dramatically following canopy closure.
Fuels changed over the 37-year sample period encompassed by this project. Specifically, 1000-hr fuels were initially high after the fire, decreased to a low in mid succession, then increased again by 35 years after the fire. Duff depth increased over time, and canopy coverage and ladder fuels reached a peak in mid-succession.
Using field data as a reference, FVS poorly modeled fuels in this system, underestimating litter and duff while overestimating fine woody fuels. However, Behave Plus simulations suggested that crown fires were most likely to occur in younger stands and decreased in likelihood with stand age, which was consistent with field data.
Fuels data suggest a constant potential for surface fires through succession in this system, but a higher potential for crown fires in mid-succession – a pattern that may affect management efforts on fire prevention and suppression efforts over time. Acknowledging that managers always assess current conditions when managing for fire, understanding how vegetation and fuels change over time to influence flammability in this system is an essential decision-making aid for managers. The changes in potential fire behavior with time – with the probability of crown fire decreasing in older stands rather than the more conventional opposite trend - further reiterate that large fires in temperate jack pine-dominated ecosystems are more strongly controlled by weather systems than by the fuels complex. The inability of FVS to accurately model fuels in jack pine systems in this project implies the need for further study of the model itself; such work might examine whether jack pine in this region is an outlier systems in terms of model predictions or whether the Lake States Variant of FVS might be improved.
