Forests are a major carbon reservoir and provide multiple ecosystem services. In the Pacific Northwestern USA high elevation dense conifer forests have co-evolved with fire resulting in a disturbance-recovery dynamic that eventually returns to a forested landscape. Drier and warmer conditions are expected as the climate changes in the region, which could favor a stable vegetation state characterized by hardwood and shrub species as the result of changing disturbance (fire) and recovery rates. It is thus imperative that we assess the potential for a critical transition from mixed conifer forest to a scrubland-hardwood ecosystem. We used LANDIS-II, a forest landscape model, to simulate the potential for an alternative stable state to the current high dense conifer forest in one of the most carbon rich and diverse forests of the USA, the Klamath Region. The model simulates changes in tree and shrub composition as a function of disturbance, dispersal, and succession. It uses life history attributes and species growth rates and simulates the C and N cycling through vegetation and soils. Fire is simulated as a dynamic spread process affected by fire weather, fuel properties of the vegetation, and topography. We compared model results across 4 different climate change scenarios.
Results/Conclusions
The model was able to confidently capture current patterns of biomass (error 15% of original plot biomass) and historical fire regimes. Climate change simulation corroborated the high potential for a critical transition in the Klamath region, notably through the interaction of increased incidence of fire; and slower forest recovery rates. Most climate change scenarios projected drier conditions for the area, which translated to slower successional dynamics and an increased role of inter- and intraspecific competition. Our simulations demonstrate that there is a potential for climate change to accelerate rapid vegetation shifts.