Drivers Of Future Ecosystem Change In The Us Pacific Northwest: The Role Of Climate, Fire, And Nitrogen

The US Pacific Northwest (PNW) is home to a wide array of ecosystems and climates. Because of its dry summers, the PNW was sensitive to large-scale climate perturbations in the past and may be vulnerable to climate change during the coming century. In this chapter we explore the resilience and vulnerability of PNW ecosystems with the MC1 vegetation model. MC1 was run with historical and future climates using a range of projections and model configurations. Fire frequency increased ubiquitously, but the domain remained a carbon sink in most scenarios because of increased productivity in nonsummer months. Thresholds of summer drought were exceeded such that the maritime forests lost a large amount of carbon (24%) due to fire in the most extreme climate projection. Fire suppression changed the magnitude, but not the sign, of future changes, and may become less effective at limiting future burned area. The representation of nitrogen mainly affected tree-grass competition in arid shrublands. Overall, simulations suggest the PNW has the potential to either sequester or emit approximately 1 pg C over the next century, or roughly 23 times the size of Oregon and Washington's combined annual fossil fuel emissions.